Margaret M. Loos
The Human Energy System comes in assorted sizes, shapes and types, but they are built of basically the same structural units, the cells. These cells number approximately thirty to one hundred trillion in an adult. The cells differ in structure and function. Most of them are capable of reproducing themselves (renewable) with the exception of those which are highly specialized, such as the brain cells whose number is fixed in the very young, and the heavily minerally deposited bone cells. If we view each cell as a separate living entity (ignoring their inter-reliance) they share those characteristics which we attribute to a typical cell. They are miniature organisms that ingest, digest and excrete food. They have a respiration system that provides oxygen that “burns” the food. Each cell is an energy system that can utilize the simple compounds that are the end products of the body’s digestion to burn as fuel to provide energy. If they stop functioning in this way, they die. The turnover, except in those that cannot reproduce themselves, is unending.
The metabolism of a cell is divided into catabolism and anabolism. Catabolism is the process by which large food molecules are broken down to smaller ones and liberate energy. This energy is necessary for all cellular activity. Some of the energy is in the form of heat, and some is used to maintain the mechanical work of the cell, and to activate small molecules are united to form larger ones and in doing so, consume energy. Anabolism utilizes energy to or synthesize cellular products for growth, repair and reproduction.
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Input
,
Output
, and
Storage
The three types of food that the cells are capable of accepting and using are:
1. Carbohydrates, in simple (hexose) sugar form.
2. Proteins, in the form of simple amino acids.
3. Fats, in the form of glycerol and fatty acids.
When these units are oxidized directly as in the case of carbohydrate sugars or fats, or indirectly as in the case of proteins that first must be converted to carbohydrates and fats, they produce energy.
Their yield varies:
|
1 gram of carbohydrate
|
4.1 calories
|
|
1 gram of fat
|
9.3 calories
|
1 gram of protein
|
4.1 calories
2
|
|
(after conversion)
|
The energy thus produced can take the form of the skin; therefore the surface area of the individual determines the amount of energy (heat) lost. The average man has a total surface area of 1.8 square meters, the average woman, 1.6 square meters.
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Those excess calories that are not utilized for energy are stored in the body in the form of fat in enlarging fat cells. Weight is gained. Proteins which cannot be stored in the body are either used to form new
protoplasm
for growing or reproducing cells or are converted to fats which may be stored.
Units and Definition
The unit of energy derived from oxidation of food or fuel is the calorie. The calorie is the amount of energy required to raise the temperature of one gram of water one degree, from 15° Celsius to 16° Celsius. A more convenient unit in a body’s energy system is the
Kilocalorie
or
Calorie
or the amount of energy required to raise the temperature of one
kilogram
(1,000 grams) of water from 15° Celsius to 16° Celsius.
Physics defines energy as the
ability to do work
. Work, in turn, is defined as
force
X
distance
. When we lift our arm against the force of gravity we do work whether it is lift a bundle or to wave at a friend or to gyrate to music. If a body is sustaining itself as an energy system it maintains cells, provides new materials for growth (anabolism), loses energy as heat through the skin principally, and according to the activity uses additional calories.
|
Type of Work
|
Additional Calories/Hours of Work
|
|
Light
|
50 Calories
|
|
Moderate
|
50Ð100 Calories
|
|
Hard
|
100Ð200 Calories
|
|
Very Hard
|
200 Calories or more
4
|
Essentials of Diet
Any diet that is sensible for the human organism would seem to require the important foodstuffs,
carbohydrates
,
proteins
, and
fats
. In addition,
vitamins
and
minerals
must be provided to act as catalysts and co-enzymes that enable vital chemical processes to take place in the cells’ energy producing structures, the
mitochondria
.
Roughage
adds bulk to the flow of food through the digestive system.
Water
is absolutely necessary since all these processes in the cells can take place only when the materials are in solution and since the body is 65%
water.
When we discuss diet, especially with the young, we should distinguish between hunger and appetite.
Hunger
is the complex condition that is accompanied by vigorous contractions of the empty stomach, a feeling of emptiness in the abdomen, and a general discomfort that cannot be localized.
Appetite
is the craving for a certain food or drink which can be satisfied quite easily.
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Worldwide Diet
With these facts we can now approach modern “diets”. The world as a whole has a diet that can be broken down in this way:
|
Cereals
|
56%
|
|
Roots and tubers
|
7%
|
|
Fruits and vegetables
|
10%
|
|
Sugar
|
7%
|
|
Fats and Oils
|
9%
|
|
Livestock and fish
|
11%
6
|
The average adequate diet in the Far East is 2,300 calories; in North America, 2,700 calories. Climate is a factor. Physiologists give an average figure as 2,400.
Proteins in Particular
In addition, protein intake must be emphasized since it is absolutely necessary for body growth and maintenance. The needs of the body for protein vary with age.
|
Age
|
Grams/kg Body Weight (Kg = 2.2 pounds)
|
|
3-5 Years
|
3.0 grams
|
|
5-15 Years
|
2.5 grams
|
|
15-17 Years
|
1.5 grams
|
|
Above 21 Years
|
1.0 grams
7
|
These depend on the quality of protein consumed and the requirements of the individual for an active and healthy life higher but “ . . . in the early sixties nutritionists in the U.S. recommended (for adults) 60 grams including at least 10 grams of animal protein as the minimum
level of intake.
”
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Worldwide Problems
in
Diet
The condition that occurs when a person (especially a child) is deprived of calories, high-quality protein, or both, is called malnutrition. Protein-calorie malnutrition affects from one-half to two thirds of the children under five in poor countries (Eckholm and Record, 1976, Telliffe, 1973) and an estimated ten to twenty million people, mostly children, die from protein-calorie malnutrition and its associated diseases each year. . . .Also, “Severe malnutrition in early childhood can stunt the physical and intellectual development of children that survive past the age of five.”
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One modern problem of nutrition has arisen in the area of infant nutrition. A great concern has been felt recently because breast feeding is on the decline in the poorer countries of the world. Commercial companies have distributed sample formula preparations to introduce them to new mothers. When the mothers use these, the stimulus of nursing is eliminated and lactation ceases. The expense of the commercial preparations is often too high for the young mothers. Also in these areas the water for reconstituting the formula may be contaminated and illness and death sadly follow. Another problem is that nursing mothers ordinarily have longer times between pregnancies, a natural means of lowering population figures, and a benefit that is eliminated by the formula use. A boycott of censure has been instituted against the Nestle’s Company, one of the major manufacturers of these formulas. A code restricting this abuse was passed by the U.N. in May, 1981 and voted for by every country in that body except the United States, which voted against it, viewing it as a restriction of trade.
So we see that diet and accompanying energy production in the body is a worldwide concern for this and future generations. Many factors encourage us to re-examine our diets.
-
1. Expense (especially in an inflationary period).
-
2. The need to reduce ecological stress caused by increased food production.
-
3. Health reasons
-
a. Relationship between fattier meats and coronary heart disease. (This) encourages the use of less beef and pork and more poultry.
-
4. Economic reasoning that some foods use up many more resources to produce and therefore cost more.
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Many scientists believe that we could work out an adequate diet for the entire world population if the major part of the diet were cereals balanced by legumes. The legumes would provide the necessary protein.
This type of diet does not have appetite appeal or cultural acceptance in many areas of the world. In addition, many nations do not even have the means to afford this dietary balance because of their extreme poverty. Ideal distribution of the nutrients would be extremely difficult. If the rate of population growth continues to increase, the output of these nutrients would have to keep doubling. The natural resources necessary to promote that output would lead to environmental degradation.