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 soybean 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 Are Fats 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.
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