4. How The Body Uses Fat
Fat is used in the body in four main ways:
- As a source of heat and energy;
- As padding and insulation for the organs and nerves;
- As a regulator for the fat soluble vitamins (A, D, E and K); and
- As a source of the essential fatty acids.
4.1 Fats Supply Heat and Energy
Each gram of fat supplies nine calories. This is more than twice the amount of energy supplied by a gram of carbohydrates. The body uses fat in much the same way as it uses carbohydrates. That is, fat is used mainly as an energy food.
Fats are converted to energy by being split into fatty acids and glycerol. Glycerol is then converted to either glucose or glycogen. At this point, the usual processes of carbohydrate metabolism take over to produce needed energy from the glucose and glycogen.
While fats may supply twice the caloric energy of carbohydrates, we find that they must undergo a longer digestive process before they are ready for an essentially carbohydrate metabolism. In general, carbohydrates do a more efficient job of providing the body with readily usable fuel. Fats are valuable in that they may provide a form of stored energy, but strictly speaking, they are not a necessity in the diet as far as a fuel source goes.
Fats, however, are usually more extensively stored within the body than are carbohydrates and may be converted into fuel when the body’s carbohydrate reserves are depleted. In fact, this is exactly what occurs when a person goes on a diet, fasts, or is exposed to extremely cold weather. As the stored carbohydrate reserves in the liver are exhausted, the body’s fat reserves are metabolized for a new supply.
It should be understood that these fat reserves in the body do not simply come from the fat that is eaten in the diet. When an excess of carbohydrates is eaten, it is converted by the body into fat and stored.
In this way, the body can store and use fat without having a large amount of fat in the diet. The fat deposits could be viewed as a carbohydrate bank, where deposits and withdrawals are made as necessary.
We can see that fat within the body is an important energy and heat source, but strictly speaking, fat in the diet is not an essential outside source for this fuel.
4.2 Fats Provide Padding and Insulation
Within the body, fat deposits provide padding and support for the organs and insulate the body from cold.
For instance, a certain amount of fat is necessary in the buttocks. A loss of most of the fat in this body area actually makes sitting down uncomfortable. Fat tissue is also a special type of connective tissue that aids in the support of certain organs, such as the liver.
Most animals in nature experience an increase in their fatty tissues with the advent of the cold weather. This fat may be used as a fuel source during the winter months when food is naturally scarce and help in the insulating of the body.
This function of fat in the body should not be confused with the role of fat in the diet. Fat reserves in the body do not necessarily come from fat intake in the diet but may instead be developed from the carbohydrates consumed.
4.3 Fats Aid in Absorption of Fat-Soluble Vitamins
Some of the vitamins are termed “fat-soluble.” This means that fatty compounds must be present in the intestines for these vitamins to be absorbed. The fat soluble vitamins are A, D, E and K. The other vitamins (B, C, etc.) are termed “water-soluble.”
If these fat-soluble vitamins are obtained from the foods in which they naturally occur and eaten in an unprocessed state, they will be readily absorbed by the body. The wholesome foods which contain these vitamins also contain the necessary fatty compounds for their absorption.
If these vitamins, however, are extracted (as in supplements) or occur in foods which have been fragmented, processed or subjected to heat, then their absorption will be impaired. Heating fatty foods, for example, renders almost all of the fat-soluble vitamins useless.
4.4 Fats Are Sources of the Essential Fatty Acids: Vitamin F
Even if no fat is eaten, the body can manufacture most of its fatty acids from fruit and vegetable sugars. There are three fatty acids, however, that the body is said to be unable to synthesize. These are called the essential fatty acids.
The three essential fatty acids are linoleic acid, arachidonic acid and linolenic acid. The linoleic acid is generally thought to be the most important and has been termed absolutely essential to life by some nutritional researchers. The arachidonic acid can act as a fairly good substitute for linoleic acid. The third acid, linolenic, is said to be only a partially satisfactory substitute for linoleic acid in that it can support growth but cannot aid in the other functions that linoleic acid performs.
Collectively, these essential fatty acids are sometimes referred to as vitamin F. The fatty acids or vitamin F are considered necessary for normal glandular activity, especially the adrenal glands. The adrenal and sex hormones seem to require the presence of these fatty acids for their manufacture.
The essential fatty acids are thought to be involved in many of the body’s metabolic processes. They promote the availability of calcium and phosphorous to the cells and help form the fat-containing portion of every cell’s structure. They are also considered a factor in growth and in reproduction.
4.6 Effect of Deficiency
A lack of vitamin F (the fatty acids) is said to contribute to skin disorders, gallstones, loss of hair, impaired growth and reproductive functions, kidney and prostate disorders and menstrual disturbances.
Since the fatty acids are also said to aid in the growth of intestinal bacteria which help produce the B vitamins, the symptoms of a B-vitamin deficiency may be related to a lack of fatty acids in the diet.
No minimum requirement for vitamin F or the essential fatty acids has been established. The National Research Council has stated that about 1% of the total daily calories of about 2200-2800 per day should consist of unsaturated fats to provide a margin of safety for the intake of essential fatty acids.
The following wholesome foods contain the shown percentages of linoleic acid, the major fatty acid. In general, if the intake of linoleic acid in the diet is adequate, then all other fatty acid needs are also well satisfied.
|Food||% Linoleic Acid|
|Raw sweet corn||Trace|
It is interesting to determine how much of the above foods would supply the 1% caloric intake of unsaturated fatty acids (in this case, linoleic acid). This is not to suggest that we accept this “1%” figure as an absolute or even as a necessity at all.
However, for the sake of argument, let’s assume a daily intake of 2500 calories. At this level, official figures tell us we should have 25 calories of unsaturated fatty acids. By examining the total amount of linoleic acid available in the nuts and seeds in our previous chart and knowing their calorie contents per ounce, we discover that anywhere from one-half to an ounce and a half of these nuts and seeds would give us 25 food calories of linoleic acid.
That is not the sum total of all the unsaturated fatty acids in these foods, nor is it the total of all the other fats we get in our daily diet. It is merely a statement that even if one-half to an ounce and a half of these nuts and seeds were consumed each day, and nothing else, we would still surpass all official recommendations for essential fatty acid intake.
This does not mean that we must eat this small amount of nuts or seeds each day. We should always eat only what the body needs or requires and not become involved with calorie counting or food weighing.
All fresh fruits, for example, contain between 0.5% and 1% unsaturated fat. Some fruits are higher in fat (particularly the avocado which may be 15% to 22% fat). If fruits alone were consumed, we would still have no difficulty meeting the government suggestion that we make 1% of our diet unsaturated fats.
- 1. Introduction
- 2. What Are Fats?
- 3. Fat Digestion
- 4. How The Body Uses Fat
- 5. Harmful Fats
- 6. The Use Of Fats In A Healthy Diet
- 7. Questions & Answers
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