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Chapter 11
Diet and Nutrition
The first part of this chapter introduces
some principles of diet and nutrition and discusses them in general terms.
Although these principles are presented primarily with the elderly in mind,
they apply to all adults. The second part presents information about specific
nutrients, including their uses in the body, dietary sources, reasons for
having abnormal levels, and problems resulting from abnormal levels. The third
part deals with abnormal conditions related to diet and nutrition.
Need for Nutritional homeostasis
A main function of the digestive system is to supply nutrients at proper and
fairly steady levels to body cells and thus maintain nutritional homeostasis.
Cells require nutritional homeostasis for four reasons. First, many nutrients
must be constantly broken down to supply the energy needed to power the ongoing
vital functions of the cells. Second, nutrients supply the raw materials needed
to synthesize body substances. Some materials are used to enlarge, replace, or
repair parts of the body (e.g., muscle cells, RBCs, epidermis); others are used
to replace substances that are degraded (e.g., neurotransmitters, hormones) or
lost (e.g., water in perspiration, digestive enzymes). Third, nutrients supply
materials that assist chemical reactions (e.g., vitamins, certain minerals).
Fourth, nutrients such as minerals and water maintain proper volumes and
concentrations of body fluids so that blood flows properly and cells are not
damaged by excessive shrinking or swelling.
Relationships Between Diet and
Nutrition
Usually, nutritional homeostasis can be maintained with a diet containing
adequate amounts and proper types of nutrients. A healthy person's digestive
system can carry out the processes involved in properly supplying the nutrients
contained in such a diet. However, many adverse conditions can inhibit the
proper functioning of the digestive system or unfavorably affect other body
systems. This results in an inability to maintain nutritional homeostasis even
though a person eats a proper diet. These adverse conditions include loss of
teeth; atrophic gastritis; inadequate lactase production; atherosclerosis;
diabetes mellitus; smoking; alcoholism; and certain medications. Therefore, it
can be said that nutritional homeostasis cannot be achieved without a proper
diet, eating a proper diet often results in nutritional homeostasis, and eating
a proper diet does not guarantee nutritional homeostasis.
See Table of Factors that
Influence Amounts and Types of Food Eaten and Table of Factors Contributing
to Malnutrition in the Elderly.
For vast information on nutrition starting at the US Department of Agriculture
web page on Food and Nutrition, go to http://www.usda.gov/wps/portal/usda/usdahome?navid=DIETARY_HEALTH&navtype=RT&parentnav=FOOD_NUTRITION
and https://www.nal.usda.gov/fnic/diet-and-health-0.
Also go to https://www.biologyofhumanaging.com/websites.htm#Nutrition
.
Problems from Malnutrition
Diversity
of Problems
A person who does not maintain nutritional homeostasis is said to have malnutrition.
This condition can cause a constellation of problems whose nature and severity
depend on the specific nutrients or combinations of nutrients that are above or
below the normal range; the amount of deviation from the normal range; and the
frequency of the deviation or the length of time it exists. Sometimes
malnutrition for one nutrient may directly affect only one body function (e.g.,
vitamin K and blood clot formation). In many other cases malnutrition for one
nutrient (e.g., protein deficiency) may affect many or all cells in the body.
However, since body cells and systems are interdependent, malnutrition that
directly affects one or a few functions ultimately has widespread effects. For
example, vitamin K deficiency leading to poor blood clotting can result in slow
but steady blood loss, anemia, and therefore a reduced oxygen supply to all
body cells.
Onset of Problems
In some cases of malnutrition problems develop quickly. For example, water
deprivation on a hot day can result in overheating within a few hours. In many
other cases problems develop gradually. In some of these cases, the diet may
provide certain nutrients at low levels and body cells may function at only a
slightly reduced or slowly diminishing capacity. For example, a slight
deficiency in B vitamins may result in a barely noticeable decline in strength.
In other cases of nutrient deficiency, the body may be able to compensate
partially by drawing on its reserves. For example, calcium deficiency may not
become apparent for many years because blood calcium levels can be maintained
by withdrawing calcium from the bones. Finally, in cases of nutrient excess the
body may be able to convert or store large quantities of the excess nutrient
and thus protect body cells from injury. For example, the liver can store much
vitamin A and reduce or delay the toxic effects of an excessive dietary intake
of that vitamin.
Nature of Problems
Besides developing gradually, manifestations of malnutrition often begin as
vague and nonspecific abnormalities such as weakness, nausea, headache, and
changes in personality. In other cases, the effects of malnutrition may seem to
result from a specific disease that is often not associated with malnutrition
(e.g., dementia). In both situations, determining that the problem is caused by
malnutrition is difficult and malnutrition is often overlooked as a cause.
Consequences
Since malnutrition is a deviation from homeostasis
(i.e., from continuing good health), body cells do not have
optimum conditions and function less effectively. This decline in cell function
leads to a decline in the ability of the body to adapt to other changes in
internal or external conditions and therefore may result in further decrements
in homeostasis. For example, calcium deficiency can lead to weaker bones that
provide less support, and then fractures from traumatic injury or ordinary
activities may occur. Similarly, protein deficiency can reduce the ability of
white blood cells to combat bacteria, and infections may occur. Finally, in
cases of excess fat and carbohydrate intakes, the obesity that may develop can
inhibit the quick movements needed to avoid an accident such as a fall.
Besides reducing adaptive responses that maintain homeostasis, the malfunctions
caused by malnutrition can substantially reduce the enjoyment derived from activities.
As examples, obesity from an excess food intake often leads to an earlier onset
of fatigue and discomfort from recreational activities, and a zinc deficiency
can lead to reductions in taste sensations and decrease the pleasure derived
from foods.
A third consequence of malnutrition is disease. Some types of malnutrition are
known to cause specific diseases. For example, iron deficiency causes anemia,
and high blood alcohol levels cause cirrhosis. Other types of malnutrition are
only risk factors or contributing factors to disease; recall the dietary risk
factors for osteoporosis and colorectal cancer (Chaps. 9 and 10).
A Proper Diet
A
Word of Caution
Since proper nutrition depends on consuming a proper diet, we will now explore
such a diet for healthy adults. One must realize that the following
recommendations may be improper for individuals who are in unusual situations
or have abnormal or disease conditions. Examples include athletes undergoing
intense physical training, people living in extremely hot or cold environments,
individuals who are bedridden, and people with diabetes mellitus or kidney
failure. Such individuals need to implement significant modifications to the
recommendations to achieve nutritional homeostasis or avoid additional problems
from their peculiar circumstances or diseases. This concept is especially
important in regard to the elderly because people become more heterogeneous
with age. Therefore, while the following recommendations can serve as
guidelines in evaluating and planning diets for groups of healthy elderly
people, they should be applied to individuals with caution.
Diet Based on Food Selection
Describing a diet in terms of commonly eaten foods is the most practical way to
select a diet that will provide nutritional homeostasis for most healthy
adults. The U.S. Department of Agriculture (USDA) has developed such a diet, My Plate. Though this plan consists of
food groups, items high in fats, oils, and sweets provide energy but few other
necessary nutrients. Foods from this group should be minimized except for
individuals who are active and need to obtain more energy.
(Suggestion 236.01.02)
(Suggestion 136.01.03)
To see old Food Guide Pyramids and the new MyPlate
updates and applications, go to http://www.choosemyplate.gov/
.
(Suggestion 237.01.Fig. 11.1)
To see information about a specialized MyPlate for elders,
go to
https://now.tufts.edu/news-releases/tufts-university-nutrition-scientists-provide-updated-myplate-older-adults
or https://www.nutritionletter.tufts.edu/healthy-eating/myplate-for-older-adults-eat-right-for-your-age
.
To download and use the MyPlate icon and related graphics, go to https://www.choosemyplate.gov/resources/myplate-graphic-resources
and https://www.choosemyplate.gov/ .
The U.S. RDAs have been replaced by the Reference Daily Intake (RDI). The list
includes only values for protein, vitamins, and minerals for use in nutrition
labeling. The values for the U.S. RDAs were essentially the same as those in
the RDIs except for protein. Food labeling information on Reference Daily
Intakes (RDIs), Daily Reference Values (DRVs), Daily Values (DVs),, and % DVs
is at "Food Labeling & Nutrition" (https://www.fda.gov/food/food-labeling-nutrition)
and "Dietary Reference Intakes" (https://www.nal.usda.gov/fnic/dietary-reference-intakes).
Information from the FDA called " Changes to the Nutrition Facts Label” is
at https://www.fda.gov/food/food-labeling-nutrition/changes-nutrition-facts-label
Information for elders from the FDA called " Understanding and Using the
Nutrition Facts Label” is at https://www.fda.gov/files/food/published/Understanding-and-Using-the-Nutrition-Facts-Label---Companion-Patient-Materials.pdf
.
Selecting recommended servings each day from the other five food groups and
varying the selections within each group will provide an adult who engages in a
fairly low amount of physical activity with adequate amounts of almost all
essential nutrients. Individuals who are more active should increase serving
sizes or, better still, increase the number and variety of servings.
Individuals who are inactive should increase their physical activity so that
they can select enough servings with enough variety to achieve nutritional
homeostasis without gaining weight. Trying to avoid weight gain by eliminating
food groups or servings from the diet can lead to a deficiency in one or more
essential nutrients.
The Food Guide Pyramid, and perhaps My
Plate, can be improved by including foods with vitamin C (e.g., citrus
fruits) from the fruit group; choosing items with minimum fat content from the
milk and meat groups; and selecting items made with whole grains from the bread
group.
Although following the Food Guide Pyramid, My Plate, and these three suggestions
will provide adequate dietary nutrients, this alone may not solve other
problems associated with an improper diet. These problems include
atherosclerosis, diabetes mellitus, tooth decay, high blood pressure,
constipation, cancer, cirrhosis, and accidents. Therefore, the USDA and the
Department of Health and Human Services have added several recommendations,
such as (1) avoiding fat, saturated fat, cholesterol, sugar, and sodium, (2)
consuming enough starch and fiber, and (3) not drinking more than a moderate amount
of alcoholic beverages.
The Food Guide Pyramids are outdated. They were replaced with My Plate, which seems to lack
information specific for elders. Go to https://www.choosemyplate.gov/
or put https://www.choosemyplate.gov/
into the place of the URL in your browser. Use the links or the Search
feature on the home page for https://www.choosemyplate.gov/
to find information on topics of interest (e.g., history of MyPlate, graphics,
and a specialized MyPlate for elders).
For a “A Brief History of USDA Food Guides” including Food Guide Pyramids, see https://myplate-prod.azureedge.net/sites/default/files/2020-12/ABriefHistoryOfUSDAFoodGuides.pdf
See also “Healthy Eating Plate” at https://www.health.harvard.edu/plate/healthy-eating-plate.
For a “A Brief History of USDA Food Guides” including Food Guide Pyramids,
see https://myplate-prod.azureedge.net/sites/default/files/2020-12/ABriefHistoryOfUSDAFoodGuides.pdf
To download and use the MyPlate icon and related graphics, go to http://www.choosemyplate.gov/print-materials-ordering/graphic-resources.html
and http://www.choosemyplate.gov/food-groups/downloads/MyPlate/MyPlateGraphicsStandards.pdf.
For information about a specialized MyPlate for
elders, go to http://www.nutrition.tufts.edu/research/myplate-older-adults
.
Also see https://www.nal.usda.gov/fnic/older-individuals.
Diet Based on Chemical Composition
Recommended Dietary Allowances
The recommendations for a proper diet based on food selection were
developed primarily to ensure that individuals could regularly obtain adequate
amounts of each nutrient. These amounts have been established by the Food and
Nutrition Board of the National Academy of Science and are referred to as the Recommended
Dietary Allowances (RDAs) of nutrients whose requirements
have been well studied. The RDAs provide enough of each nutrient to maintain
good health and are higher than the amounts needed just to survive. The RDAs
and the dietary recommendations mentioned next can be found in tables in most
textbooks on nutrition.
(Suggestion 236.02.04)
Several features of the RDAs warrant special attention. First, the
recommendations are for individuals of certain weights and heights and should
be adjusted for the individual. Second, except for infants and children, men
and women have different RDAs. Third, the RDAs group individuals into
categories based on age. Fourth, there are only two age categories for those
over age 24. These categories are ages 25 to 50 and age 51 and over. This lumps
all elderly individuals together even though it is thought that age changes
after age 51 affect nutritional needs. Though little information is available
about adjusting the RDAs to compensate for these age changes, a few
recommendations are included in the second part of this chapter.
Besides the RDAs for specific nutrients, a table of recommended energy intake
has been developed. In this table, the estimated energy requirements, indicated
as kcals, are for persons who perform light to moderate physical
activity. A kcal, or kilocalorie, also called a Calorie
(note the uppercase C), is the unit most often used to measure the energy
content in food or the energy consumed. A kilocalorie is 1,000 calories (note
the lowercase c).
Persons with body dimensions that differ greatly from those listed in the table
and individuals whose activity levels are very low (e.g., the bedridden) or
very high (e.g., athletes) may have energy requirements as much as 1,000 kcal
below or above those listed. Individuals recovering from a serious illness or
accident also often need an increased energy intake to provide the energy
necessary for healing. For any particular individual, the best way to estimate
energy requirements is to determine the energy intake needed to maintain a
desirable body weight as discussed later in this chapter.
The energy table shows that the energy requirements for people age 51 and over
are lower than those for younger adults. The decline in recommended energy
intake at higher ages is based on the average age-related decline in muscle
mass and amount of physical activity.
Calculations using the RDAs for protein intake for people age 51 and over
result in a value of approximately 0.8 gram per kilogram (0.36 gram per pound)
of body weight. Other authorities suggest that the elderly can benefit from a
protein intake of 1.0 gram per kilogram (0.45 gram per pound) of body weight
while reducing energy intake from carbohydrates and fat. This modification can
assure an adequate protein intake while preventing weight gain since elderly
people tend to have lower energy requirements.
U.S. Recommended Daily Allowances
Though the RDAs are listed as daily allowances, a person need not
consume each nutrient in the recommended amount each day because the body can
store excess nutrients and release the stored nutrients when lesser quantities
are eaten. A person need only consume enough of each nutrient over a few days
or a week so that the average amounts consumed each day correspond to the RDAs.
To assist consumers and those evaluating and planning diets, the Food and Drug
Administration used the values in the RDAs to develop the U.S.
Recommended Daily Allowance (U.S. RDA) for many
nutrients. The age categories for U.S. RDAs are even broader than those for
RDAs, placing all individuals above age 3 into one category.
The labels on many packaged foods list the percentages of the U.S. RDA for many
nutrients. This information is useful in determining the nutrient quality of
foods and the contribution each food item can make to a person's daily nutrient
intake.
Estimated Safe and Adequate Daily Dietary Intakes The lists of RDAs do not include all
required nutrients. Estimates of requirements for other nutrients have been
made by the
Food and Nutrition Board and are listed as Estimated Safe and Adequate
Daily Dietary Intakes (ESADDIs). This list places all
adults into one category regardless of age.
(Suggestion 238.01.05)
The ESADDIs are published in Recommended Dietary Allowances: 10th Edition, Food
and Nutrition Board, Commission on Life Sciences, National Research Council
(1989). A free on-line version can be seen and downloaded by going to http://www.nap.edu/catalog/1349.html
. Some ESADDIs are in the Summary Table on page 284 and at http://www.nap.edu/openbook.php?record_id=1349&page=284
.
Dietary Reference Intakes
The Dietary Reference Intakes (DRIs) make up a new
comprehensive method for establishing and evaluating recommended dietary intake
recommendations. This new system is under development, and some DRIs for specific
nutrients have been established. The DRIs will supplant other systems on which
it is based.
(Suggestion 238.01.07)
An on-line version of the reference book Dietary Reference Intakes:
Applications in Dietary Planning (2003) from the Food and Nutrition Board and
the Institute of Medicine is at http://www.nap.edu/books/0309088534/html/
.
The tables of Dietary Reference
Intakes are at http://www.nap.edu/download.php?record_id=10872#,
.and more information about DRIs from the National Academy of Sciences is at http://nationalacademies.org/hmd/Activities/Nutrition/SummaryDRIs/DRI-Tables.aspx
.
The DRIs are based on a combination of Recommended Dietary Allowances
(RDAs), Estimated Average Requirements (EARs),
Adequate Intakes (AIs), and Tolerable Upper
Intake Levels (ULs). These four systems have different
goals. The RDAs provide adequate intake to give 97 percent of a population
adequate intake. The EARs provide adequate intake to give 50 percent of a
population adequate nutrient. The AIs list the average intake for a population
that will give a desired predetermined outcome (e.g., risk of a disease) based
on outcomes from actual diets in that population. The ULs list maximum intakes
in an actual population that provide 97 percent to 98 percent of the population
with no adverse risks or effects from the high levels of intake.
Because the DRIs are based on systems with diverse standards and goals,
different portions of the DRIs should be used in different circumstances so the
desired outcomes are most likely to be achieved. Different portions of the DRIs
satisfy different percentages of a population. Also, different levels of the
DRIs are being set for different types of populations (e.g., age groups, body
size, percent body fat, gender, health status, cultures, etc.). The DRIs will
use 12 life stages (i.e., 0-6 months, 6-12 months, 1-3 years, 4-8 years, 9-13
years, 14-18 years, 19-30 years, 30-50 years, 51-70 years, 71+ years, and
pregnant and lactating women). Different aspects of the DRIs can be used for
planning diets, for assessing diets, or for assessing outcomes from programs
affecting diets (e.g., institutional meal plans, school meal plans).
(Suggestion 238.02.02)
To see all the Recommended Dietary Allowances (RDAs) and the Dietary Reference
Intakes (DRIs), go to https://www.nal.usda.gov/fnic/dietary-reference-intakes
and search for "dietary reference intakes". Then search for
specific dietary components (e.g., vitamins, minerals, water, macronutrients,
electrolytes, etc.).
To calculate DRIs for an individual, go to https://www.nal.usda.gov/fnic/dri-calculator/index.php.
Comparing Proper Diets for Younger and
Older Adults
A comparison of proper diets for healthy younger adults and healthy older
adults reveals that with very few exceptions, these diets are basically the
same. The exceptions include slight increases for the elderly in fiber,
protein, and calcium intakes, while total energy and vitamin A intakes should
be somewhat lower. If the diets of healthy, active younger and older adults
were compared, the recommended differences in protein and total energy intakes
would be eliminated, making the diets even more similar. The reason for this similarity
is that the types and total amounts of cellular activities and therefore the
nutritional needs of healthy active adults remain essentially the same
regardless of age. However, increasing age is often accompanied by a decrease
in physical activity, unusual situations, abnormal changes, and diseases, all
of which may require individualized dietary adjustments.
For nutrition information, exercise, and recommendations for the elderly, go to
http://nutritionandaging.fiu.edu/
. It is developed by the National Resource Center on Nutrition, Physical
Activity & Aging. Also go to a list of web pages at Web Sites/Nutrition
at https://www.biologyofhumanaging.com/websites.htm#Nutrition
.
Malnutrition Among the Elderly
Malnutrition is widespread and occurs frequently among the elderly. Providing
precise estimates of the extent of malnutrition and the specific nutrients
involved is difficult. Interestingly, many cases occur even when adequate food
and professional assistance are available, such as in nursing homes. The high
incidence of malnutrition among the elderly is due to many factors, many of
which become more common or severe with age. These factors may be biological,
social, psychological, or economic.
See Table of Factors that
Influence Amounts and Types of Food Eaten and Table of Factors Contributing
to Malnutrition in the Elderly.
For a list of factors contributing to malnutrition among the elderly, see https://www.biologyofhumanaging.com/tblmal
- true.htm .
Reducing and
Preventing Malnutrition
Though the factors causing extensive malnutrition among the elderly are
numerous and diverse, the following steps can be taken to reduce malnutrition
in this segment of the population.
Evaluating Nutritional Status To
reduce and prevent malnutrition, one must determine which individuals are malnourished
and what types of malnutrition they have. Several approaches are used in making
such determinations. These include developing a dietary history; keeping
records of food intakes; performing physical examinations; performing chemical
analyses of blood samples; analyzing records of body weight; and taking body
measurements such as skin fold thickness, height, and weight. The values
obtained are compared with the recommended values. Combining two or more of
these approaches provides determinations of nutritional status having increased
accuracy and reliability.
Identifying Factors Contributing to Malnutrition Once cases and types of malnutrition have
been identified, the second step is to attempt to identify factors that have
contributed to the malnutrition. Though this may be difficult, correcting
malnutrition is easier if the causes can be reduced or eliminated.
Evaluating and Adjusting Diet A
third step in solving malnutrition is to compare individuals' diets with
dietary recommendations based on My
Plate, RDAs, U.S. RDAs, and ESADDIs. When one uses these general guidelines
and tables, individualized diets can be designed to provide nutritional
homeostasis while minimizing problems that may be caused or amplified by
specific dietary components.
See Table of Factors that
Influence Amounts and Types of Food Eaten and Table of Factors Contributing
to Malnutrition in the Elderly.
Implementing dietary adjustments can be a difficult task because many factors
besides hunger caused by low nutrient levels influence the amounts and types of
foods people eat. Some of these factors (e.g., taste preferences) influence
voluntary choices. Others (e.g., religion, culture, disease) impose dietary
requirements or restrictions. Considering these factors improves the likelihood
that recommended dietary adjustments will be adopted.
Many elderly people are able voluntarily, independently, and effectively to
implement dietary modifications and changes in exercise to improve their
nutritional status. However, any others require regular assistance. Effective
programs for these people are provided by government agencies, social
organizations, and volunteer groups.
(Suggestion 239.02.05)
Using Supplements For some
individuals, eating a proper diet or implementing dietary adjustments cannot
adequately reduce or prevent malnutrition or cannot do so quickly enough.
Examples include people taking certain medications (e.g., antibiotics);
individuals who have or are recovering from certain diseases (e.g., atrophic
gastritis, diverticulitis); people recovering from surgery or from certain
types of injury (e.g., burns); and individuals who are smokers or alcoholics.
In many of these cases the desired nutritional levels can be attained through
other means, such as taking dietary supplements (e.g., fiber, vitamins,
minerals) and drinking extra water. Other individuals are helped by taking
medications that affect appetite or alter the absorption of specific nutrients
such as cholesterol.
Supplements and medications should be taken only when nutritional homeostasis
cannot be achieved through diet and evidence suggesting the presence of a
specific nutrient deficiency is available. Inappropriate ingestion of nutrient
supplements can lead to additional malnutrition, toxicity, and serious or
life-threatening malfunction or failure of many body systems because of (1)
age-related decreases in mechanisms, such as nutrient storage, conversion, and excretion,
that permit adaptation to excess materials and (2) the likelihood that excess
nutrients will aggravate existing problems or cause new ones in weakened organs
or systems.
A Continuing Process The
processes involved in maintaining nutritional homeostasis and reducing and
preventing malnutrition should be viewed as ongoing even after malnutrition has
been identified and rectified. Evaluation of nutritional status should continue
since adjustments may be necessary as age changes occur and new situations and
conditions arise. Examples include (1) the onset of, worsening of, or
improvement in a disease, (2) changes in social situations (e.g., family
structure), (3) alterations in psychological status (e.g., grief, life review
process), and (4) modifications in economic conditions (e.g., declining real
income).
Energy and Body Weight
Energy
Uses and Storage
The supply of energy from nutrients must be continuous because homeostasis
(i.e., continuing good health)
and
survival require that vital functions never cease. Since people eat
intermittently rather than continuously, only some of the energy from food is
used immediately after its nutrients have been absorbed. The remaining energy
is stored in reserves until needed.
Most reserve energy is stored as fat in fat cells and as glycogen in the liver
and in muscle cells. The body draws on these reserves when energy supplies from
the nutrients being absorbed are lower than energy demands. The body can obtain
energy from body proteins, but it usually does this only after most of the glycogen
and fat reserves have been used because proteins make up essential body
components.
Dietary Sources of Energy
Most energy from foods is obtained from carbohydrates, lipids,
and proteins (see Chapter 2). The carbohydrates in foods are
either single sugar molecules such as glucose or larger molecules made of
combinations of sugar molecules. Common examples include the disaccharides
sucrose (table sugar) and lactose (milk sugar) and the polysaccharides starch
and glycogen. Dietary lipids occur in a variety of forms, though usually more
than 90 percent of them are in the form of triglycerides, which
are also called fat on food labels. Other dietary lipids include cholesterol,
monoglycerides, diglycerides, and phospholipids.
Disaccharides and polysaccharides are broken down into single sugar molecules
before being absorbed into the body. Most sugars are converted into glucose by
the liver before being transported by the blood to other cells. Fat is also
broken down before absorption but is reconstituted before entering the
circulatory system. Proteins are broken down into amino acids before they are
absorbed.
Obtaining Energy from Molecules
Energy in sugar, fat, and amino acid molecules is contained in the
chemical bonds that hold the atoms composing each molecule together. Cells
convert this energy into forms they can use by breaking the chemical bonds and
transferring the released energy into motion, other chemical bonds, or heat.
Glucose molecules can yield useful energy almost immediately as they pass
through a series of chemical reactions called glycolysis, which
takes place in the cell cytoplasm. Glycolysis converts only approximately 5
percent of the energy in a glucose molecule into an immediately useful form.
Some of the energy is released as heat, and the rest is in the remaining
fragments of the glucose molecule. These fragments enter the mitochondria,
where they are broken down further by complicated processes called the Krebs
cycle, electron transport, and oxidative
phosphorylation. More than half the energy released from glucose
and other sugar molecules by these processes appears as heat. Most of the
remaining energy is placed into adenosine triphosphate (ATP).
The energy in ATP is used to power vital processes such as moving,
manufacturing substances and body components, and transporting materials.
Fat and amino acids must also be broken down partially before they can release
useful energy. Most of the fat and amino acid fragments enter the mitochondria,
where chemical reactions convert most of their energy into heat and ATP
molecules. Note that the initial partial breakdown of amino acids produces a
toxic waste material (ammonia), which is immediately converted into a harmless
substance called urea. The kidneys pass urea into urine for elimination.
The breakdown of molecular fragments from sugar, fat, and amino acids by
mitochondrial processes requires the addition of oxygen and results in the
formation of CO2 and H2O. If the oxygen supply is
inadequate, glucose fragments are converted to lactic acid while
most fat and amino acid fragments accumulate as ketones (ketoacids).
Therefore, having an inadequate supply of oxygen limits energy extraction and
leads to an excessive buildup of lactic acid or ketoacids, which disturb
acid/base balance. Energy extraction can also be affected by limitations in the
number of mitochondria, as occurs in unexercised muscle cells. Therefore, when
oxygen supply or mitochondrial numbers are low, weakness and fatigue may
result.
Kilocalories Comparing the energy
contents (kilocalories) of carbohydrates, fat, and proteins reveals that for a
given weight of a nutrient (e.g., 1 gram or 1 ounce), carbohydrates and
proteins contain nearly the same amount of energy. A sample of fat of the same
weight contains approximately twice as much energy.
The high energy content of fat may lead to difficulties in interpreting labels
on packaged foods. For example, a label indicating that a food is 95 percent
fat-free may mean that only 5 percent of the weight of the food is fat.
However, more than half the kilocalories may come from the fat since much of
the remaining weight may come from water or other low-calorie components.
Energy Balance
If the total energy intake over a period equals the total amount of energy used
by the body during that period, the body is in energy balance. If
the energy intake is greater than the energy used, the body has a positive
energy imbalance. The extra energy is stored as fat and glycogen,
causing a gain in weight. If the energy intake is less than the energy used,
the body has a negative energy imbalance. Additional energy needs
are met by breaking down stored fat and glycogen, causing a loss of weight.
Energy Use The energy used by
the body can be placed into several categories. One category includes the
energy needed to sustain body functions when a person is awake and in a state
of complete rest. These conditions are called basal conditions, and the rate of
energy use is called the basal metabolic rate (BMR).
About 20 percent of BMR energy use is due to muscle cells. Some of this energy
is used by the few muscle cells that contract for breathing and for maintaining
muscle tone, though muscle cells that are not contracting also use energy to
tear down and rebuild their internal components. Although all cells constantly
undergo this process of turnover, muscle cells account for a large proportion
of the BMR energy used because of the relatively large amount of muscle tissue
in the body. Therefore, individuals with more muscle mass have higher BMRs.
Additional energy is used by muscles for respiration and heartbeat.
Other portions of BMR energy are used by turnover activities in other cells and
in the normal replacement of cells in the skin, blood, GI tract lining, and in
the uterine lining after menstruation. About 40 percent of BMR energy is used
by ongoing brain and liver activities. Finally, some of this energy is used to
keep the body warm. In children, the energy needed for growth adds to these
uses. The BMR for an average young adult is approximately 1 kcal per minute, or
1,440 kcal per day.
A second portion of the energy used by the body powers the processes involved
in digestion. This energy may constitute approximately 5 percent to 10 percent
of the body's daily energy use. A third portion goes into muscle contractions
during physical activity. Since the amount of an individual's physical activity
usually varies greatly from one day to the next, so also does the amount of
energy used. Days involving light physical activity (e.g., writing letters,
talking with friends) may add a few hundred to more than 1,000 kcal of energy
use to basal energy needs. Days involving many hours of strenuous physical
activity (e.g., carpentry, caring for a household with children, hiking) may
double the body's energy use at basal conditions.
A fourth portion of body energy use serves defensive and healing functions. For
example, much energy is used to maintain a high fever, combat a major infection
or widespread cancer, or recover from surgery, a burn, or another extensive
injury. Like the energy for physical activity, this type of energy use is quite
variable and can exceed the amount used at basal conditions. Pregnant women use
energy in a fifth way by supporting the development of a fetus.
Age-Related Changes in Energy Use
Aging is usually accompanied by a decrease in BMR energy use that is
mostly caused by declining muscle mass. The BMR energy use from non-muscle mass
remains basically unchanged or declines slightly with age. A decline in
non-muscle BMR energy use may result from slower cellular turnover or
replacement, slower synthesis of secretions by glands, and, in women, cessation
of menstruation.
Though some of the decline in muscle mass is due to age changes in muscles,
frequently a much larger proportion of the decline in muscle mass, and
therefore in BMR energy use, results from decreased physical activity. Adults
who remain physically active as age increases retain much of their muscle mass
and have a small decline in BMR energy use. Furthermore, sedentary elderly
people who increase their muscle mass through exercise have increases in BMR
energy use.
There is probably no significant change in energy use from digestive processes
in healthy aging adults. However, certain diseases of the digestive system may
increase (e.g., GI tract spasms) or decrease (e.g., atrophic gastritis) this
energy use.
On the average, energy used for physical activity decreases with age. The
reasons for this decline include age changes; physical and mental disabilities;
diseases; retirement; children reaching adulthood and needing less care;
institutionalization changes in priorities; and following the preconceived or
stereotyped sedentary lifestyles of the elderly. However, aging individuals can
maintain or increase their level of physical activity and thus maintain or
increase their energy use for physical activity.
Since many defense and healing processes occur more slowly with age, their
rates of energy use may also decrease with age. However, since the number, frequency,
and severity of problems requiring these processes seem to increase with age,
the total amount of energy use for these processes may also increase.
Combining age-related changes in the five categories of energy use results in
an average continuous decline in energy use with age. Estimates of energy use
for men ages 23 to 50, 51 to 74, and 75 and above are 2,700 kcal a day, 2,400
kcal a day, and 2,050 kcal a day, respectively. The corresponding estimates for
women are 2,000 kcal a day, 1,800 kcal a day, and 1,600 kcal a day. These
values are estimated averages for healthy adults performing light physical
activity. The actual values for individuals may vary from these estimates by
more than 1,000 kcal a day depending on body size, amount of physical activity,
and health status.
Age-Related Changes in Energy Balance
On the average, changes in body weight, muscle mass, and bone material
suggest that there is a positive energy imbalance until about age 50. After
that, there is at most a slightly negative energy imbalance. However, many
older individuals vary significantly from the average and have substantial
positive or negative energy imbalances.
For many people beyond age 50, energy balance is fairly well maintained while
the total amount of energy intake and use declines substantially. At the same
time, the amounts of almost all nutrients needed by the body seem to remain
stable or increase. This means that to obtain all required nutrients in
adequate amounts while consuming a diet with fewer kilocalories, the foods
being consumed must have higher concentrations of nutrients relative to the
kilocalories contained in those foods. The ratio of the amount of a specific
nutrient to the number of kilocalories in a portion of food is called nutrient
density. Foods in the fats, oils, and sweets group in My Plate have a very low nutrient
density.
A better way to ensure an adequate intake of all required nutrients while
maintaining energy balance is to increase energy use by increasing physical
activity. This allows a person to eat more food while avoiding a positive
energy imbalance, which can lead to excess body weight from a disproportionate
amount of body fat. This strategy also increases the other benefits derived
from regular exercise.
Overweight and Obesity
To understand what excess body weight and a disproportionate amount of body fat
mean, one must establish values for desirable body weight and percent body fat.
Problems
Increased by Obesity
For the U.S. National Library of Medicine
and NIH comprehensive web site about obesity, go to http://www.nlm.nih.gov/medlineplus/obesity.html
.
For “Clinical Guidelines on the Identification, Evaluation, and Treatment of
Overweight and Obesity in Adults” by the National Heart, Lung, and Blood
Institute, go to http://www.ncbi.nlm.nih.gov/books/NBK2003/
For a PDF file of report on obesity, go to http://www.nhlbi.nih.gov/guidelines/obesity/ob_gdlns.pdf
. Go to page 12 of the report for the section on health risks and other
outcomes from obesity (e.g., social, psychological). For the NHLBI BMI
calculator, go to http://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm
For the NHLBI web page with tips and information about overweight, go to http://www.nhlbi.nih.gov/health/public/heart/obesity/lose_wt/index.htm
.
For the Centers for Disease Control and Prevention web site on “Overweight and
Obesity”, go to
http://www.cdc.gov/nccdphp/dnpa/obesity/index.htm
. It has links to diverse topics about obesity and weight control (e.g.,
contributing factors, trends, consequences, recommendations, BMI calculators) .
For the Merck comprehensive web site about obesity, go to http://www.merckmanuals.com/home/disorders-of-nutrition/obesity-and-the-metabolic-syndrome/obesity
.
For the Endocrine Society's web site about obesity and Obesity In America, go to http://obesityinamerica.org/ .
Also see https://www.biologyofhumanaging.com/websites.htm#Nutrition
.
Using Tables Several tables of
desirable body weights for people without serious disease have been developed.
A table from the Metropolitan Life Insurance Company is based on the assumption
that the weights of individuals with the longest life spans represent desirable
body weights. The National Health and Nutrition Examination Surveys (NHANES)
table and the Andres table include values for older people. The Andres table
also considers the average age-related increase in the proportion of body fat
resulting from loss of muscle tissue. Though these tables provide guidelines
for desirable body weights, factors such as body frame size and amount of
muscle tissue should be considered in establishing the desirable body weight
for an individual.
(Suggestion 243.01.02)
Using Body Mass Index Another
way to determine whether a person has a desirable body weight is to find the body
mass index. This value is calculated by dividing the person's
weight in kilograms by the square of the person's height in meters. Values
between 25 and 30 are considered desirable because people whose body mass
indexes are within this range have the greatest longevity and the lowest risk
of contracting diseases such as diabetes mellitus and high blood pressure. Those
whose body mass index is above 40 have considerably reduced longevities and are
at high risk for a variety of weight-related diseases.
Using Percent Body Fat Percent
body fat can be determined in several ways. These include measuring the
thickness of skin folds at one or more places; measuring how much electrical
resistance the body provides; and comparing a person's weight in air with body
weight when that person is completely submerged in water.
Desirable percent body fat values for adults are considered to be 15 to 18
percent for men and 20 to 25 percent for women. Adults with values above 25
percent for men and 30 percent for women have shorter longevities and higher
risks for developing weight-related diseases. Since the risks are somewhat higher
for individuals with high concentrations of fat around the waist rather than
the thighs, determining the ratio between the circumference of the waist and
that of the hips gives a further indication of desirable percent body fat.
Waist-to-hip ratios should be less than 0.9 for men and less than 0.8 for
women.
Definitions We can now define
terms indicating deviations from accepted standards. People whose body weights
are 10 percent to 20 percent greater than the desirable body weights can be
considered overweight. People whose body weights are more than 20
percent above the desirable body weights can be considered obese
if their percent body fat exceeds 25 percent (men) or 30 percent (women) or if
their body mass index is more than 30. Very muscular individuals whose weight
is more than 20 percent above desirable body weights but whose percent body fat
is less than 25 percent (men) or 30 percent (women) are overweight but are not
considered obese.
Consequences Being overweight
but not obese has little effect on a person's longevity or risk of developing
weight-related disease. Some authorities suggest that in general elderly people
may benefit from being slightly overweight because the extra energy stored in
their body fat helps them maintain nutritional homeostasis and endure the
adverse effects of periods of illness or other undesirable circumstances.
(Suggestion 243.02.04)
Though being slightly overweight may be beneficial, obesity is accompanied by
increases in the incidence of a variety of problems, a greater negative impact
from these and other problems, and lower longevity. The incidence and
seriousness of weight-related problems are directly related to the degree of
obesity. Longevity is inversely related to the degree of obesity.
Problems
Increased by Obesity
For a list of problems increased by obesity, go to https://www.biologyofhumanaging.com/tblobese
- true.htm .
Prevention and Correction The
best way to avoid the consequences of obesity is to avoid becoming obese. This
is much easier than trying to lose weight once obesity has developed.
Furthermore, recurring and significant fluctuations in weight decrease
longevity and increase the risk of developing weight-related disease.
(Suggestion 243.02.04)
One of the most important steps in avoiding obesity as age increases is to
maintain energy balance by decreasing total energy intake when energy use
decreases. A key sign that this action is appropriate is a significant increase
in weight.
See Limiting Intake of
Fat, Saturated Fat, and Cholesterol.
Another important step is staying physically active to maintain a high level of
energy use. Physical activity keeps energy use high both directly and by
helping to maintain a large muscle mass, which sustains a high BMR energy use.
It can also help keep energy intake down by suppressing appetite, distracting
attention from eating, promoting interest in diverse activities while
preventing boredom, and supporting a healthful psychological state. Finally,
since people who get plenty of exercise can eat more and not gain weight, they
have a higher chance of obtaining adequate amounts of all necessary nutrients
without becoming obese (Chap. 8).
Solving obesity by losing weight and decreasing percent body fat can be very
difficult since many factors may contribute to obesity. Key features in a
successful program to lose weight include getting a physical examination;
developing a long-range plan for gradual weight loss and weight maintenance;
decreasing energy intake while eating foods with high nutrient densities;
exercising; and receiving monitoring regularly to prevent malnutrition and
other problems.
Underweight
Having a weight below the range for desirable body weight is called being underweight.
The negative energy imbalance that causes a person to become underweight may
result from inadequate energy intake, a reduced ability of the digestive system
to make energy-containing nutrients available to the body, or excessively high
energy use.
Consequences Being underweight may
have several undesirable consequences. These including muscle weakness;
fatigue; lethargy; increased risk of low body temperature; reduced resistance
to infection; and decreased ability to tolerate periods of adversity such as a
prolonged
disease. Since being underweight is often but not always accompanied by
deficiencies in specific nutrients, body malfunctions and other problems are
also commonly present, including specific diseases resulting from nutrient
deficiencies. This variability helps explain why some people with very low body
mass index seem to have a greater mean longevity, while others have a reduced
mean longevity.
Often, being underweight results in slightly lower longevity for underweight
persons or those who have a body mass index below 20. Some scientists believe
that the decline in longevity is directly related to the degree to which a
person is underweight, while others believe that having a low body mass index
increases mean longevity. Adverse effects from being underweight may be greater
for the elderly than for young adults.
Prevention and Correction
Preventing being underweight involves avoiding a negative energy
imbalance. This may involve increasing energy intake when activity levels
increase. When a substantial drop in weight becomes apparent, dietary energy
intake may be increased, correction of or compensation for digestive system
difficulties may be implemented, or activity levels may be reduced. These
strategies also can be used to correct a chronic underweight condition. As with
solving obesity, correcting underweight conditions in elderly persons requires
special awareness of and attention to each individual's particular
circumstances.
Carbohydrates
Digestible
Carbohydrates
Common dietary carbohydrates come in several forms. Some of them may be monosaccharides
such as glucose and fructose, which are abundant in many packaged foods and
fruits. However, a major portion of dietary carbohydrate consists of disaccharides
such as sucrose, which is found in table sugar and in most sweet foods, and
lactose, which is found in milk and milk products. Sucrose consists of glucose
and fructose, and lactose consists of glucose and galactose. The other major
dietary carbohydrate molecules are polysaccharides. The most
common digestible polysaccharides are starch, which is found in plant foods,
and glycogen, which is found in meats. Both are made of glucose molecules.
The specific disaccharides and polysaccharides mentioned thus far are broken
down into individual monosaccharides before being absorbed. Once absorbed,
galactose and much fructose are converted into glucose by the liver. The
remaining fructose is broken down by a process similar to glycolysis.
Indigestible Carbohydrates: Fiber
Many polysaccharides in foods from plants cannot be broken down by digestive
enzymes. These indigestible polysaccharides are called fiber.
Fiber that does not dissolve in water is called insoluble fiber
and includes cellulose, hemicellulose, and some
noncarbohydrate material (lignin). Fiber that dissolves in water is called soluble
fiber and is abundant in most fruits and vegetables, especially oats
and beans.
Uses
Sugars The body uses glucose and
fructose as sources of energy. Some cell types, such as brain cells and red
blood cells, rely almost exclusively on glucose for energy, and active muscles
and the heart consume large quantities of sugars for energy. Since glucose is
an excellent energy source, the liver makes it from fragments of amino acid
molecules and lactic acid. Only a small amount of glucose can be made from fat
because only the glycerol portion in fat can be converted into glucose.
Some glucose helps supply energy by transferring many fragments from fat and
amino acid molecules into the Krebs cycle. Without glucose, these fragments can
yield no energy and are converted into ketoacids. Fragments from sugar
molecules are also used to manufacture fat, other lipids, parts of amino acids,
and sugar molecules in DNA and RNA.
When the blood contains more sugar than the cells require, much of the sugar is
stored as glycogen or is converted into fat for storage. The level of blood
sugar is controlled by several hormones.
Fiber Since fiber cannot be
digested, the sugar molecules of which it is made cannot be absorbed and used
in the body. However, dietary fiber is essential for good health because it
stimulates intestinal motility by providing bulk. In this way, it promotes
proper intestinal functioning and helps prevent several disorders of the large
intestine. Furthermore, soluble fiber reduces the risk of atherosclerosis by
decreasing the absorption of cholesterol. It can also help diabetics by slowing
the absorption of glucose.
Recommended Dietary Intakes
Ample energy from digestible carbohydrates can be obtained by eating 50 to 100
grams of digestible carbohydrate a day. Individuals who are quite active should
consume more digestible carbohydrate. Another guideline is to consume 55 to 60
percent of the total energy intake as digestible carbohydrates. Most of this
intake should be in the form of starch or glycogen.
Daily fiber intake can range between 20 and 35 grams per day and probably
should be close to the higher value. Individuals with a low fiber intake
probably should increase it gradually to allow the GI tract to adjust to the change
in diet. Individuals with special problems such as constipation,
diverticulosis, atherosclerosis, and diabetes mellitus may benefit from higher
fiber intake.
Carbohydrate Deficiencies
Deficiencies in digestible carbohydrates are rare because many foods have large
quantities of these nutrients. However, if such a deficiency develops, body
cells lack adequate energy. The consequences of a low energy supply include
weakness, lethargy, and reduced mental functioning. In addition, fat and amino
acid fragments that cannot be channeled into the Krebs cycle are converted into
excess ketoacids, which disturb homeostasis by altering acid/base balance and
causing excess sodium and potassium loss in the urine.
Inadequate fiber intake is a common problem. Several undesirable results, such
as problems with the large intestine, were mentioned in Chap. 10.
Carbohydrate Excesses
Consuming excess digestible carbohydrates is common because foods high in
carbohydrates are relatively inexpensive and because sweet foods are pleasant
to eat. Eating excess sugars promotes tooth decay and, by suppressing the
appetite, reduces the intake of other important nutrients. For example, some
elderly people suffer from protein-carbohydrate malnutrition (PCM)
because the carbohydrate-rich foods they eat in abundance contain little
protein. A high carbohydrate consumption is also often accompanied by
undesirable weight gain and hampers maintenance of blood glucose homeostasis.
A high fiber intake can lead to deficiencies in calcium, zinc, and iron because
fiber inhibits the absorption of these nutrients. Excess fiber consumption also
hampers maintenance of water homeostasis because fiber binds water in the large
intestine and therefore reduces water absorption. For this reason, individuals
on high-fiber diets should drink large quantities of water.
Certain types of indigestible carbohydrates result in gas production in the
large intestine. Therefore, foods such as beans and peas, which contain high
amounts of these substances, can cause discomfort and embarrassment.
Lipids
The body can convert the lipids contained in foods into almost all the other
types of lipids it needs. It can also synthesize most types of lipids from
carbohydrates and proteins. For example, the liver can manufacture cholesterol.
Though lipids are a diverse group of substances, most dietary lipids fall into
only a few categories. We will examine glycerides and cholesterol here (Chap.
2).
Tri-, Di-, and Monoglycerides and Fatty
Acids
The most abundant dietary lipids are triglycerides, which consist
of three fatty acid molecules attached to a glycerol
molecule. Triglycerides are also called fat on food labels and may be either
solid or liquid (oils) at room temperature. Many foods contain monoglycerides
and diglycerides, which contain one or two fatty acids,
respectively. Monoglycerides and diglycerides are not called fat. Therefore,
they are not included as part of the fat content listed on food labels even
though they contain and give the body the same components as do triglycerides.
The fatty acids in fat may be saturated or unsaturated.
Unsaturated fatty acids may be monounsaturated or polyunsaturated.
Unsaturated fatty acids differ from one another not only in chain length and
number of double bonds but also in the locations and orientations of those
bonds. Foods from plants have higher proportions of monounsaturated and
polyunsaturated fatty acids, while foods of animal origin have higher
proportions of saturated fatty acids.
Naturally occurring unsaturated fatty acids in foods, including those in fat,
may have hydrogen added during processing. Fatty acids and fat treated in this
way are said to be partially hydrogenated or hydrogenated.
Hydrogenation makes the fatty acids and fat more solid and thus improves the
texture of some foods.
Two fatty acids are of special importance because they are essential parts of
body molecules and must be obtained in the diet since they cannot be
manufactured by the body. Therefore, these two fatty acids—linoleic acid and
alpha-linoleic acid—are referred to as essential fatty acids.
These fatty acids are also called omega-3 fatty acids because of the location
of a double bond. Fat in plant oils and fish oils have high levels of these
fatty acids.
Cholesterol
The other important dietary lipid is cholesterol. This substance,
which has a molecular structure resembling chicken wire, is found only in foods
from animals. Foods high in cholesterol include those containing egg yolks,
cream, and fat from meats.
Uses
Dietary lipids have several functions. They make some foods more pleasant by
improving flavor and texture and producing a sense of fullness and
satisfaction. They also aid the absorption of vitamins A, D, E, and K. Lipids
that have been absorbed are used to produce bile, supply energy, and build body
components and chemicals (e.g., fat tissue, cell membranes, vitamin D, steroid
hormones). The two essential fatty acids are used in building cell membranes
and producing a variety of chemicals that help regulate diverse processes,
including blood clotting, stomach secretion, and immune system functioning.
Recommended Dietary Intakes
Since diets in the United States typically contain more lipids than are needed,
many dietary recommendations for adults provide upper rather than lower limits
for dietary lipids. In general, fat should account for less than 30 percent of
total daily energy intake, and saturated fat and polyunsaturated fat should
each account for less than 10 percent. Cholesterol intake should be below 300
mg per day. Many steps can be taken to keep dietary lipid intakes below these
limits, and the absorption of dietary cholesterol can be reduced somewhat by
diets high in soluble fiber.
Lipid
Deficiencies
Individuals with lipid-deficient diets may have low energy levels and
deficiencies in fat-soluble vitamins. Diets lacking sufficient plant or fish
oils do not provide enough essential fatty acids, resulting in varied
disorders, including abnormalities in blood clotting, blood pressure, and
immune system functions.
Lipid
Excesses
Diets containing excess lipids promote several problems, including indigestion,
obesity, colon cancer, atherosclerosis, and possibly breast cancer.
See Limiting Intake of
Fat, Saturated Fat, and Cholesterol.
For tips on limiting fat intake, see also https://www.biologyofhumanaging.com/tblfats
- true.htm .
When fat and cholesterol are absorbed by the small
intestine, they combine with other lipids (phospholipids) and blood proteins to
form droplets of lipoprotein. Lipoproteins are also formed using
fat and cholesterol made by the liver in cases of positive energy imbalance,
especially when it is severe enough to cause obesity. Since all these
lipoproteins contain much fat and are relatively very light, they are called very
low-density lipoproteins (VLDLs). Much of the fat in
VLDLs is removed and used by body cells. The remaining particles are not as
light and are called low-density lipoproteins (LDLs).
LDLs are removed from the blood by liver cells and other cells that have
receptors for them. Liver cells eliminate the cholesterol from the LDLs they
receive by excreting it into bile or converting it into other useful materials.
Other body cells store much of the cholesterol in the LDLs they receive. When
cells lining blood vessels store LDL cholesterol, it initiates the formation of
atherosclerotic plaques.
Since diets low in saturated fat help liver cells remove LDLs from the blood,
less LDL enters other cells and less plaque formation occurs. Conversely, diets
high in saturated fat inhibit liver cells from removing LDLs from the blood,
and cells in vessels remove the LDLs and form plaques. Therefore, plaque
formation is kept low by low-saturated-fat diets and is raised by
high-saturated-fat diets.
The number of double bonds and their locations in unsaturated fatty acids
influences their amount of risk for atherosclerosis. Monounsaturated fatty
acids are less likely to produce lipid peroxides (LPs). Polyunsaturated fatty
acids (PUFAs) help keep blood LDLs low, but when they have double bonds at a
location called the omega-6 position, they promote LP formation. PUFAs with a
double bond in the omega-3 position produce less LPs and help keep blood clots
and blood pressure low.
Plaque formation is also kept low by lipoproteins called high-density
lipoproteins (HDLs), which have relatively little
cholesterol or other lipids. HDLs carry cholesterol from body cells to the
liver for elimination. This explains why a high HDL/LDL ratio partially
counters the adverse effects of high blood cholesterol and high LDL levels and
thus helps reduce the risk of atherosclerosis. One way exercise lowers the risk
of atherosclerosis is by increasing HDLs and thus lowering blood cholesterol
and LDL levels.
A total blood lipoprotein level (total cholesterol level) of approximately 200
mg per 100 milliliters of blood (200 mg/dl) is used by many people to mark the
boundary between acceptable and unacceptable blood lipid levels. Individuals
with total cholesterol levels substantially above 200 mg/dl have a much higher
risk of developing atherosclerosis, while individuals with levels well below
200 mg/dl have a rather low risk. Having LDL levels above 165 mg/dl or HDL
levels below 35 mg/dl also implies a substantial risk.
Many individuals can maintain healthful cholesterol and lipoprotein values or
improve poor values by eating foods with much soluble fiber, avoiding dietary
cholesterol and saturated fat, sustaining the recommended weight through energy
balance, and exercising. These steps can substantially reduce the risk of
developing atherosclerosis.
(Suggestion 247.02.04)
Proteins
Foods high in protein include meat and fish, egg whites, milk, beans, and peas.
Proteins from animal products contain all 20 types of amino acids; plant
proteins often lack or have very little of one or more types. Since different
plant foods lack different amino acids, a complete set of amino acids can be
obtained from plants by eating specific combinations of plant foods (e.g., rice
and beans, corn and beans).
Uses
Digestive enzymes break dietary protein molecules into individual amino acids,
which are then absorbed into the blood. Body cells use fragments from some
amino acids for energy and to build nonprotein molecules. Other amino acids are
used to build body proteins.
Body cells require large supplies of all 20 types of amino acids to build
proteins. If even one type is missing or is in very short supply, synthesis of
body proteins virtually stops. Although 11 of the 20 types can be manufactured
in abundance by the liver and other cells, adequate amounts of the other nine
types cannot be made in the body and must be supplied by dietary proteins.
These amino acids are called essential amino acids.
Body proteins made from dietary amino acids have many uses. Many are used to
build cell membranes, keratin (epidermis), collagen and elastin fibers (dermis,
ligaments, cartilage), and muscle cell microfilaments. Others are used as
enzymes to control chemical reactions; hormones to send messages; antibodies to
fight infections; buffers to regulate acid/base balance; clotting factors to
stop bleeding; blood proteins to help transport lipids (lipoproteins); and
blood proteins to control the movement of water through capillary walls. Body
protein molecules are broken down and their amino acids are used for energy
only under starvation conditions.
In people of all ages body proteins such as keratin, muscle cell
microfilaments, and digestive enzymes are continuously lost or broken down.
Since the body has very limited stores of amino acids, a regular intake of
dietary proteins is necessary for the continuous replacement of these structures
so that their functions, and therefore homeostasis, are maintained.
Recommended Dietary Intakes
The RDA of 0.8 to 1.0 gram of protein per kilogram of body weight per day for
elderly people should be increased at least to 1.0 gram per kilogram per day.
Even higher protein intakes may be appropriate for individuals who must produce
extra proteins, such as people recovering from a serious injury or disease and
those engaged in very strenuous physical training. Diets with a reduced protein
content may be recommended for individuals with certain kidney diseases because
such diets yield less urea. Diets containing mostly animal proteins rather than
plant proteins also generate less urea because a higher proportion of the amino
acids from animal proteins can be used to build body proteins. With reduced
urea production, less urea must be eliminated by the kidneys and a urea buildup
in the body is avoided. This is important because excess urea can harm body
cells.
Protein Deficiencies
Since proteins contribute to many body structures and perform many functions,
diets low in one or more amino acids needed for protein production cause many
problems. Examples include structural and muscle weakness; slowed body
reactions; increased risk of infection; loss of acid/base homeostasis; excess
bleeding; edema; and poor recovery from injury.
Protein Excesses
Extra amino acids from excess dietary proteins can be used for energy or
converted into other useful materials and stored fat. Therefore, diets
containing more than the recommended amounts of protein usually cause no
difficulty except the positive energy imbalance that may develop. However,
individuals with kidney disease may accumulate harmful levels of urea.
Water
Dietary water enters the body in beverages and foods. In addition, some is
produced in the body by the complete breakdown of carbohydrates, lipids, and
proteins. Water leaves the body in feces, urine, and perspiration and by
evaporation from the respiratory system.
Uses
Dietary water aids the digestive system by dissolving materials, lubricating,
transporting materials by bulk flow and diffusion, and reacting chemically.
Once in the body, water serves the same purposes. It also helps regulate body
temperature by distributing heat and eliminating heat through evaporation.
Water helps cushion, maintain cell size through osmotic pressure, and regulate
acid/base balance.
Body water is in three areas: the blood, the spaces between cells
(intercellular space), and within cells (intracellular space). Water moves in a
controlled manner between these areas. Both the total amount of water in the
body and the proportionate distribution of water among these three areas are
essential for healthy survival.
Recommended Dietary Intakes
One aspect of maintaining homeostasis is maintaining water balance, or
obtaining as much water as is lost. On the average, an adult can maintain water
balance by ingesting approximately 2 liters of water a day. The breakdown of
nutrients supplies the 350 ml of additional water needed each day to achieve
water balance. However, the amount of dietary water supplied may require
considerable adjustment because water loss can vary greatly between individuals
and from time to time. Factors that increase water loss include high
environmental temperatures, low humidity, vigorous exercise, alcohol
consumption, fever, vomiting, diarrhea, several kidney diseases, and various
medications. In addition, individuals who spit frequently, such as those who
chew tobacco, lose much water in the saliva they expectorate.
Water Deficiencies
Advancing age is accompanied by an increasing risk of water deficiency because
of decreases in both the sensation of thirst and the control of water loss in
urine. Many elderly people have disabilities that restrict their access to
water. Others have elevated water loss from medications that reduce high blood
pressure or edema. Furthermore, increasing fiber in the diet without
simultaneously increasing water intake or eating a diet very high in fiber will
raise the risk of water deficiency because fiber inhibits the absorption of
dietary water. Since several potent factors can lead to water deficiency among
the elderly, monitoring older individuals’ water intake and output is advisable
for care givers in clinical care and institutional settings.
Individuals who do not ingest enough water to maintain water balance may suffer
from any of a variety of abnormalities, including (1) low blood pressure and
the consequences of poor circulation, (2) joint stiffness, (3) sunken eyes, (4)
dryness of the eyes, mouth, or skin, (5) sagging and wrinkling skin, (6)
diverse brain malfunctions, (7) constipation, (8) reduced kidney functioning,
and (9) urinary stones.
See Body Water, Sodium,
Potassium, and Acid Abnormalities & Effects from Deviations.
For a list of problems from having too little body water, go to https://www.biologyofhumanaging.com/tblurn
- true.htm .
Water
Excesses
Ingesting too much water seems to be uncommon among the elderly. Those who do
so may experience high blood pressure or edema.
See Body Water, Sodium,
Potassium, and Acid Abnormalities & Effects from Deviations.
For a list of problems from having too much body water, go
to https://www.biologyofhumanaging.com/tblurn
- true.htm .
Vitamins
Characteristics
Vitamins are a diverse group of substances that have five features in common.
1. They are needed in relatively small
quantities.
2. They are essential because certain
chemical reactions cannot occur effectively without them.
3. They must be obtained in the diet
because the body cannot make them in adequate amounts.
4. They must be eaten regularly because
they are stored in limited quantities and are gradually lost.
5. A deficiency in each vitamin results
in at least one specific disorder.
One main group consists of the fat-soluble vitamins (vitamins A, D, E,
and K), so called because they dissolve in fat. See the videos "Vitamins
and Minerals" (https://blausen.com/en/video/vitamins-and-minerals/)
and "Overview of Vitamins and Minerals" (https://blausen.com/en/video/overview-of-vitamins-and-minerals/).
Fat-soluble vitamins are efficiently absorbed only if there
is some fat in the diet. They can be stored in fairly large quantities in the
liver and other areas of the body that contain high concentrations of fat.
All other vitamins are water-soluble vitamins. The body is less
able to store these vitamins because they move freely among the
water-containing spaces and are easily lost in the urine.
Sources
Vitamins are found in different amounts in various foods. Since no single food
contains adequate amounts of all the vitamins, maintaining vitamin homeostasis
requires one regularly to eat a variety of foods. A diet based on MyPlate may
provide a healthy adult of any age with adequate amounts of all vitamins (https://www.choosemyplate.gov/ or put
https://www.choosemyplate.gov/
into the place of the URL in your browser). More age-adjusted information is at
MyPlate for elders (http://www.nutrition.tufts.edu/research/myplate-older-adults
and https://www.nal.usda.gov/fnic/older-individuals)
and “Healthy Eating Plate” (https://www.health.harvard.edu/plate/healthy-eating-plate).
Using vitamin supplements to augment dietary intake is generally not
recommended because this can reduce the dietary intake of other nutrients and
because high levels of certain vitamins can injure body cells and cause other
disorders (e.g., diarrhea). However, vitamin supplements may be necessary for
individuals who do not eat enough varieties or quantities of food and people
with abnormal conditions. Such conditions include ones that prevent adequate
absorption or use of vitamins and ones that cause excess destruction or
elimination. Vitamin supplements may also be used to treat certain diseases
(e.g., vitamin D for osteoporosis). Supplements with vitamins A, C, and E, and
β-carotene, which serve as antioxidants, seem to reduce the risk of
certain diseases related to damage from free radicals (e.g., atherosclerosis,
Alzheimer's disease, cancer).
Deficiencies and Excesses
Many cases of vitamin deficiency among the elderly result from eating too
little food or a limited variety of food because of alcoholism or other
unfavorable factors. Furthermore, some deficiencies develop because vitamins
are destroyed or lost when foods are washed, cooked, or processed in other
ways. Studies of vitamin status among the elderly show that deficiencies in
vitamins A, D, B6, B12, and C; thiamine; riboflavin; and folate occur
frequently. Examples of adverse changes from deficiencies in these vitamins
include: infections and disorders of the skin and eyes (vitamin A); weak bones
(vitamin D); anemia and poor functioning of the nervous and immune systems,
excess blood homocysteine (vitamin B6); anemia and nervous system malfunction,
excess blood homocysteine (vitamin B12); edema and poor healing (vitamin C);
muscle weakness and nervous system malfunctions (thiamine); inflammation of the
mouth and skin, and poor vision (riboflavin); anemia and poor functioning of
the nervous and digestive systems (folate). Vitamin excesses are rare and
almost always result from ingesting vitamin supplements.
Vague or nonspecific symptoms such as nausea, loss of appetite, and mental,
emotional, or personality changes may occur with many cases of mild vitamin
deficiency or excess. Other adverse changes that are specific for each vitamin
deficiency may be barely detectable at first.
See Facts About Vitamins.
For detailed information about vitamins, go to https://www.biologyofhumanaging.com/tblvit
- true.htm .
Minerals
Characteristics
Like vitamins, minerals are a diverse group of substances. Minerals are also
similar to vitamins because they must be obtained in the diet since the body
cannot make them, they must be eaten regularly since gradual loss depletes the
body's limited reserves, and specific disorders often accompany deficiencies or
excesses of each mineral. See the videos "Vitamins and Minerals"
(https://blausen.com/en/video/vitamins-and-minerals/)
and "Overview of Vitamins and Minerals" (https://blausen.com/en/video/overview-of-vitamins-and-minerals/).
Minerals are different from vitamins in that some minerals (e.g., calcium,
phosphorus, sodium, potassium) must be obtained in large quantities. In
addition, though some minerals (e.g., zinc, magnesium, copper, selenium) assist
certain chemical reactions, many others form parts of body compounds and
structures. Phosphorus in DNA and calcium in bones are examples.
See Facts About
Individual Minerals.
For detailed information about minerals, go to https://www.biologyofhumanaging.com/tblmnrls
- true.htm .
(Suggestion 250.02.01)
Sources
The previous statements about vitamins in food supplements are also applicable
to minerals.
Deficiencies and Excesses
Common among the elderly, the causes of mineral deficiencies are essentially
the same as those of vitamin deficiencies. Several types of mineral
deficiencies result from inadequate absorption. Many other mineral deficiencies
develop because of excess mineral elimination resulting from diarrhea, kidney malfunction,
or medications that increase mineral elimination by the kidneys. Deficiencies
in calcium lead to weak bones; deficiencies in iron lead to anemia, weakness,
and reduced immune system functioning; and deficiencies in zinc lead to slow
healing, decreased immune system functioning, poor taste perception, and male
impotence; deficiencies in selenium prevent certain enzymes from eliminating
free radicals.
The most common mineral excess may be sodium excess from ingesting foods
containing salt, which is added to improve flavor. An excess salt intake
promotes water retention and therefore increases blood pressure. Other mineral
excesses result from consuming diets high in specific minerals or from
ingesting mineral supplements.
As with vitamins, slight to moderate deficiencies or excesses in minerals may
cause only vague and nonspecific symptoms and subtle adverse changes in the
body.
See Facts About
Individual Minerals.
Nutrition and Alcohol
Alcohol consumption and alcoholism occur frequently among the elderly, just as
they do among younger adults. Light or moderate alcohol consumption by healthy
adults seems to have the same effects regardless of age. For example,
occasional modest consumption probably does not affect nutrition, but it seems
to lower the risk of atherosclerosis. However, heavy consumption, whether
occasional or frequent, adversely affects nutrition and eliminates any effects
alcohol has on reducing atherosclerosis. The effects may be greater as age
increases because of age changes and reduced reserve capacities in some organs,
more many diseases and more advanced stages of disease, and greater use of
medications.
Alcoholism (chronic heavy alcohol consumption) often causes deficiencies in
many nutrients because alcoholics are less able to plan or obtain a proper
diet, eat less, and suffer damage to the digestive system that decreases its
ability to provide nutritional homeostasis. Some alcoholics can be helped nutritionally
by taking supplements to reduce deficiencies. Alcoholism also lowers HDL
levels.
See Effects of Alcoholism
on Nutrients.
Nutrition and Medications
The use of medications increases with age, and many medications used by elderly
individuals have adverse effects on nutrition. However, the effects of some
medications and combinations of medications are not well understood. Other
factors, such as age-related modifications in the body's storage, metabolism,
and elimination of medications, further complicate the effects of medications
on nutrition.
Medications may alter nutrition by affecting many factors. These include mental
or emotional state; physical ability and coordination; food selection (because
of incompatibility with a medication or its schedule of administration);
appetite; the senses of taste and smell; GI tract secretions and motility; GI
tract bacteria; and nutrient absorption, storage, use or elimination.
Conversely, foods can decrease the effectiveness of some medications by
reducing their absorption by the GI tract (e.g., antibiotics) and can increase
the effects of medications by reducing their elimination by the liver.
Many other age-related factors contribute to an age-related increase in the
number and the severity of problems from medications. Examples include
age-related increases in use of non-prescription drugs; number of medications
taken per person; number of physicians and pharmacies used per person; decrements
in sensation and cognition; erroneous compliance.
Nutrition and Disease
Proper diet and nutritional homeostasis promote survival and help prevent many
diseases. Conversely, poor diets and malnutrition lead to the development of
many abnormal conditions and diseases (e.g., atherosclerosis, osteoporosis,
digestive system disorders) and amplify their consequences. Furthermore,
age-related abnormal conditions and diseases (e.g., emphysema, dementia,
digestive system diseases) contribute to poor diet and malnutrition.
Nutrition and Maximum Longevity
Animals in laboratories are often provided with food at all times. The food
provides contains a balance of nutrients. The animals can eat as much as they
want any time they want. Animals able to eat freely in this way are said to be
fed ad libitum (AL). In other cases, the food
provided and the times it is provided are restricted. These animals are
undergoing dietary restriction (DR).
In 1937, McCay reported that DR rats that were provided 33 percent less food
than the amount eaten by AL rats had significant increases in meal longevity
(ML) and maximum longevity (XL). Since then, DR has resulted in increases in ML
and in XL for many types of animals including roundworms, spiders, insects, and
mice.
Attempts to identify the means by which DR increases ML and XL revealed that
the essential factor is the reduction in calories eaten by the animals. As long
as the animals are fed balanced diets, only the number of calories eaten
affects both the ML and the XL consistently. The types of nutrients in the diet
and the times of eating do not cause the increases in ML and XL. Therefore,
dietary restriction is now called caloric restriction (CR).
CR animals have undernutrition without having deficiencies in any particular
nutrient (e.g., protein, lipids, minerals, vitamins). Though extreme CR (e.g.,
60 percent CR) leads to unhealthy underweight conditions, undergoing reasonable
CR (e.g., 30 percent CR) and being underweight from malnutrition are different
entities.
(Suggestion 251.02.05)
Effects from CR
Though many other treatments can increase ML in animals and in humans, CR is
the only means known to increase the XL of animals. Therefore, scientists
believe that CR actually slows fundamental aging processes. Research with CR in
monkeys and in humans is underway. CR has been shown to increase ML in monkeys.
In rats and mice (i.e., rodents), CR increases ML and XL by 25 percent to 30
percent. Animals undergoing CR also develop fewer diseases, develop diseases at
later ages, and develop milder forms of disease. CR has different degrees of
effect on ML, XL, and diseases depending upon when CR begins, how severe it is,
and how long it lasts. CR has detrimental effects if it begins during early
development, but after that, the earlier it begins, the greater the effect.
Also, the longer CR lasts, the greater the effect.
CR causes many beneficial effects in the animals in which it has been tested.
These effects may contribute to the increases in ML and XL and the reductions
in diseases. Most of the effects relate to the causes of aging proposed in the
theories of aging (see Chapter 2). However, the mechanisms by which CR
increases ML and XL and reduces disease are not known.
Specific benefits from CR include slowing the age-related increases in the
following: free radical production; free radical damage; protein cross-links
and protein glycation; lipofuscin formation; mitochondrial damage; blood
pressure; blood LDLs; blood triglycerides; blood glucose; blood insulin;
obesity; diabetes mellitus; percent body fat (usually); IL-6; kidney disease;
and cancers. CR slows or delays the age-related declines in HDLs; number of
muscle cells; rate of protein synthesis; DNA repair; insulin sensitivity; certain
hormones (e.g., melatonin, DHEA); immune function (usually); IL-2; physical
activity; and general health (e.g., skin, cardiovascular, kidneys).
Exercise produces many of these effects. Scientists have shown that CR does not
increase ML and reduce diseases in the same ways that exercise produces these
effects. Though both CR and exercise increase ML and reduce diseases, their
effects are independent, not synergistic. The effect on ML in animals having
both CR and plenty of exercise equals the sum of effects on ML seen in
sedentary animals with only CR and the effects seen in AL animals with plenty
of exercise. Finally, exercise does not affect XL.
How animal studies with CR can be applied to human aging is still being
determined. The effects of CR on humans are still unknown. Unlike animals, humans who subsist on diets
containing few kilocalories or low protein, such as people living in poor and
overcrowded areas, have shorter mean longevities. No individuals like that ever
exceed the maximum human longevity of 120 years. Of course, these CR people do
not eat carefully compounded and analyzed laboratory feeds and do not live in
the controlled environment of a laboratory, receiving inoculations, continuous
monitoring, and ongoing professional care. Could humans living most of their
lives in such conditions and eating limited amounts of only certain selected
types and quantities of food at specified times every day have greater maximum
longevity? Would an increase in maximum longevity be worth the effort? How much
could longevity be increased by CR among people living more conventional
lifestyles? If the mechanisms by which CR works are discovered, will it be
possible to produce those mechanisms in humans without requiring them to
undergo CR? Future research may eventually answer these questions.
For the Wikipedia
on-line encyclopedia site on caloric restriction, go to http://en.wikipedia.org/wiki/Caloric_restriction
.
For the NIA web page on caloric restriction, go to https://www.nia.nih.gov/site-search/caloric
restriction .
For the Caloric Restriction Society web site, go to http://www.crsociety.org/ .
©
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Copyright 2020: Augustine G. DiGiovanna, Ph.D.,
Salisbury University, Maryland
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