Did you ever wonder where your energy comes
from, and how it is derived from the foods you eat? The truth is, we get energy
from carbohydrates, fats and protein, and when you go on restrictive diets, you
short-change some systems in your body, and short-change your health.
Humans require food substances to supply the
components necessary to build tissues, to repair tissues as they wear out and
die, to keep the body in good working condition, and to supply fuel for energy.
A well-balanced diet is one that provides an adequate amount of each of the
classes of nutrients each day, furnishing at the same time an adequate but not
excessive number of calories for the body’s energy needs. Children require
relatively larger amounts of nutrients and calories because of their rapid
growth. The foods required for proper nutrition fall roughly into three major
groups: proteins, carbohydrates, and fats.
Carbohydrates are the human body’s key source
of energy, providing 4 calories of energy per gram. When carbohydrates are
broken down by the body, the sugar glucose is produced; glucose is critical to
help maintain tissue protein, metabolize fat, and fuel the central nervous
system.
Glucose is absorbed into the bloodstream through the intestinal wall. Some of
this glucose goes straight to work in our brain cells and red blood cells,
while the rest makes its way to the liver and muscles, where it is stored as
glycogen (animal starch), and to fat cells where it is stored as fat. Glycogen
is the body’s auxiliary energy source, tapped and converted back into glucose
when we need more energy.
Starches and sugars are the major
carbohydrates. Common starch foods include whole-grain breads and cereals,
pasta, corn, beans, peas, and potatoes. Naturally occurring sugars are found in
fruits and many vegetables; milk products; and honey, maple sugar, and sugar
cane. Foods that contain starches and naturally occurring sugars are referred
to as complex carbohydrates, because their molecular complexity requires our
bodies to break them down into a simpler form to obtain the much-needed fuel —
glucose. Our bodies digest and absorb complex carbohydrates at a rate that
helps maintain the healthful levels of glucose already in the blood.
In contrast, simple sugars, refined from
naturally occurring sugars and added to processed foods, require little
digestion and are quickly absorbed by the body, triggering an unhealthy chain
of events. The body’s rapid absorption of simple sugars elevates the levels of
glucose in the blood, which triggers the release of the hormone, insulin.
Insulin reins in the body’s rising glucose levels, but at a price: Glucose
levels may fall so low within one to two hours after eating foods high in
simple sugars, such as candy, that the body responds by releasing chemicals
known as anti-insulin hormones. This surge in chemicals, the aftermath of
eating a candy bar, can leave a person feeling irritable and nervous.
Many processed foods not only contain high
levels of added simple sugars, they also tend to be high in fat and lacking in
the vitamins and minerals found naturally in complex carbohydrates.
Nutritionists often refer to such processed foods as junk foods and say that
they provide only empty calories, meaning they are loaded with calories from
sugars and fats but lack the essential nutrients our bodies need. Nutritionists
caution that most Americans need to eat more complex carbohydrates. Foods rich
in complex carbohydrates, which provide vitamins, minerals, some protein, and
dietary fiber and are an abundant energy source, should make up roughly 50
percent of our daily calories.
Fats, which provide 9 calories of energy per
gram, are the most concentrated of the energy-producing nutrients, so our
bodies need only very small amounts. Fats play an important role in building
the membranes that surround our cells and in helping blood to clot. Once
digested and absorbed, fats help the body absorb certain vitamins. Fat stored
in the body cushions vital organs and protects us from extreme cold and heat.
Fat consists of fatty acids attached to a
substance called glycerol. Dietary fats are classified as saturated,
monounsaturated, and polyunsaturated according to the structure of their fatty
acids. Animal fats – from eggs, dairy products, and meats – are high in
saturated fats and cholesterol, a chemical substance found in all animal fat.
Vegetable fats – found, for example, in avocados, olives, some nuts, and
certain vegetable oils – are rich in monounsaturated and polyunsaturated fat.
High intake of saturated fats can be unhealthy.
While we need cholesterol, we do not need it in our diet. The liver, and to a
lesser extent the small intestine, manufacture all the cholesterol we require.
When we eat cholesterol from foods that contain saturated fatty acids, we
increase the level of a cholesterol-carrying substance in our blood that harms
our health. Saturated fatty acids – found in foods ranging from beef to ice
cream, to mozzarella cheese to doughnuts – should make up no more than 10
percent of a person’s total calorie intake each day. Excessive saturated fats
are considered harmful to the heart and blood vessels because they are thought
to increase the level of LDLs (the “bad” cholesterol), and decrease the level
of HDLs (the “good” cholesterol).
Monounsaturated fats – found in olive, canola,
and peanut oils – appear to have the best effect on blood cholesterol,
decreasing the level of LDLs and increasing the level of HDLs. Polyunsaturated
fats – found in margarine and sunflower, soybean, corn, and safflower oils –
are considered more healthful than saturated fats. However, if consumed in
excess (more than 10% of daily calories), they can decrease the blood levels of
HDLs. Choosing a diet that is low in fat and cholesterol is critical to
maintaining health and reducing the risk of life-threatening disease.
Protein: Although protein provides 4 calories
of energy per gram, the body uses protein for energy only if carbohydrate and
fat intake is insufficient. When tapped as an energy source, protein is
diverted from the many critical functions it performs for our bodies.
Dietary proteins are powerful compounds that
build and repair body tissues, from hair and fingernails to muscles. In
addition to maintaining the body’s structure, proteins speed up chemical
reactions in the body, serve as chemical messengers, fight infection, and
transport oxygen from the lungs to the body’s tissues.
Proteins are made up of smaller units called
amino acids. Of the more than 20 amino acids our bodies require, eight or nine
cannot be made by the body in sufficient quantities to maintain health. These
amino acids are considered essential and must be obtained from food. When we
eat food high in proteins, the digestive tract breaks this dietary protein into
amino acids. Absorbed into the bloodstream and sent to the cells that need
them, amino acids then recombine into the functional proteins our bodies need.
Animal proteins, found in such food as eggs,
milk, meat, fish, and poultry, are considered complete proteins because they
contain all of the essential amino acids our bodies need. Plant proteins, found
in vegetables, grains, and beans, lack one or more of the essential amino
acids. However, plant proteins can be combined in the diet to provide all of
the essential amino acids. A good example is rice and beans. Each of these
foods lacks one or more essential amino acids, but the amino acids missing in
rice are found in the beans, and vice versa.
Recommended protein daily intake by experts:
- A
three month old infant: 13 g
- 4
year old child 22 g
- A
healthy woman 45 g
- A
man of average size 57 g
- A
pregnant woman 55 g
- A
breast-feeding mother 65 g
Illness and stress place an enormous demand on
the body as it builds tissue or fights infection, and these conditions require
an increase in protein consumption.
Good nutrition is reflected not only in the growth, function and energy of the
body but also in its appearance. The eyes, skin, hair, and teeth indicate
whether body nourishment is good or poor. Poor nutrition may result from
excesses in the diet as well as deficiencies; excess of certain vitamins or
minerals can produce potentially lethal disease states, and excess of
carbohydrates or fat can result in obesity.
