Physiology Of Fat. Part 2
Fats - What they are and what they do to you. The outstanding fats eaten daily in
the United States and Europe are butter, eggs, whole milk, cream, meat, fish and poultry
fats, and cheese in various combinations. These fats, at 9 calories per gram, contain
more than twice the amount of calories than protein or carbohydrate does at four calories
each per gram. As we have noted and shall describe in later chapters, excessive intake of
fats leads to the shortening of life, premature death by heart attacks and strokes,
obesity, and numerous crippling illnesses. Fats (or lipids) contain the elements of
carbon, hydrogen, and oxygen in various combinations of animal and vegetable fats.
Examples of animal fats are butter, lard, cream, milk, eggs, and the fat in meats.
Vegetable fats are soyabean oil, olive oil, cottonseed and corn oils, and peanut oils;
these are found in nuts, coconuts, avocados, margarines and other vegetable fats used in
cooking. Fats do not dissolve in water, and when pure they are odorless and tasteless.
They are found in most bodily tissues, particularly in combination with other elements,
proteins, or minerals. Fats or lipids act as vehicles for the absorption of the natural
fat-soluble vitamins such as vitamins A, D, and E. In order for fats to be utilized by
the body, they must first be digested and broken down into constituent parts before being
absorbed. They are absorbed in the following manner: After the food is masticated and
enters the stomach, the digestive system supplies its first fat enzyme called lipase, to
begin the digestion of the fat. Enzymes or ferments are unique chemical compounds
manufactured by the cells of the tissues. In the digestive tract they are vital for the
chemical breakdown of all foods before they can be absorbed.
How are fats digested? The fat enzyme of the stomach, lipase, begins its job on the
fats eaten. However, it is a rather weak enzyme, leaving most of its work to be carried
out by steapsin, the fat enzyme manufactured by the pancreas, and by bile manufactured by
the liver. In the bile are found bile acids and salts which, together with steapsin, split
the fats ingested into the smallest molecules and particles possible. These can then be
absorbed through the lining of the small intestine and pass either into the liver or
directly into the blood stream as chyle, a milky or creamy serum.
How fats are
absorbed. When the fat particles are brought to the liver, they undergo further
chemical breakdown and metabolic changes before they enter the blood stream in the form
of cholesterol, phospholipids, fatty acids, neutral fats (which are neither acid nor
alkaline), lecithin, and other fat derivatives. Much of the fat is broken down by the
liver cells into cholesterol, which is excreted into the bile and goes back again into
the intestine in various chemical forms. Once in the intestine, some of the cholesterol
is reabsorbed again along with other fats and some is excreted from the body in the bowel
movement. If the proportion of the cholesterol in the bile becomes too high, then it
precipitates out of the bile and forms gallstones, which can produce attacks of pain and
indigestion, and so often keep the surgeon busy.
Now that the fats or lipids have entered the blood stream, they circulate and are
deposited in the various bodily tissues and in the great body storehouses called fat
depots. These are located in the abdomen, on the hips, the chest, around muscles, under
the skin, in the liver, and elsewhere. The fats consumed in the diet are called exogenous
fats. The liver and other tissues, however, manufacture equally important quantities of
fats or lipids normally found in the blood stream. These are called endogenous lipids.
These lipids are manufactured from proteins and carbohydrates through certain remarkable
processes inherent in vital bodily tissues and glands such as the liver or the adrenal
glands. Energy and vital cellular constituents for the body result from these lipids.
When present to excess, their effects become devastating to humans, as shown in the
chapters on overweight and atherosclerosis. (See Chapters 7 and 3.) We now come to the
fats circulating freely in the blood stream. Let's see how they get into the artery walls
to actually damage or destroy the artery with atherosclerosis.
How fats damage or destroy your arteries. Extensive research in experimental animals has
been able to demonstrate how these lipids can leave the bloodstream and enter the artery
wall within 24 hours. The atherosclerosis produced in these animals becomes
indistinguishable from the atherosclerosis seen in human arteries. However, the exact
details of the mechanism whereby fats actually enter into the wall of the artery are not
yet known. What is known and what is important is that there is a definite ratio or
relation between the amount of fats in the blood stream and in the artery wall, and this
is surprisingly predictable in most cases. Also, the relationship of the fats in the
artery wall itself is very close to that in the bloodstream. This direct relationship
between the two seems to be in fairly constant balance. As described in the first
chapter, the artery wall consists of three different layers. If the reader can picture a
garden hose as representing the artery, it presents an innermost layer called the intima,
a middle layer called the media, and an outer layer called the serosa. (See Fig.
1). Fig. 1. Cross Section, Coronary Artery.
This diagram shows the three coats of
the coronary artery and the channel through which the blood flows to nourish the heart
muscles.
The fats circulating in the blood stream are of course closest to
the innermost layer of the artery, with which they are in direct contact. When conditions
are right for atherosclerosis, the fats attach themselves and enter the inner or intima
layer of the artery. A kind of wart or excrescence on the artery is then formed, called a
plaque of lat. When the plaque grows larger, it encroaches upon the passageway of the
artery. As it grows larger and larger, it may finally block or obstruct it partly or
completely. When this clogging or obstruction of the artery takes place in the vital
coronary arteries of the heart, then a coronary thrombosis or heart attack assails the
victim. If the blockage from these fatty or atheromatous plaques occurs in the brain,
then a stroke strikes down the victim. (See Figure 2.)Fig. 2.
Cross Section of Coronary Artery in Coronary Thrombosis.
However, if the artery is only partly blocked by this accumulation of fatty plaques, then
the vital organs supplied by the arteries suffer from a lack of the necessary amount of
blood and nutriments contained in it to sustain normal function and health. Along with
the fatty deposits of cholesterol, fatty acids, neutral fats, etc., which make up these
atheromatous plaques, calcium and other minerals are also deposited. These make the
artery feel hard, giving rise to the term commonly in use - "hardening of the arteries."
Actually we see a softening of the arteries which takes place first because of these fatty
deposits. It is often noticed in many individuals that this free fat will be floating in
the blood stream for hours after a meal containing fat has been eaten. The blood is then
called lipemic, which means loaded with fats. When these fats are easily visible to the
naked eye, scientists speak of such neutral fats as chylo-microns. These fats in the
blood are regarded by many scientists to be as dangerous as is cholesterol, in entering
the artery wall.
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