The longer-chained fatty acids with 14 carbons or more, and the mono- and diglycerides must be reconverted to triglycerides in the intestinal wall. These triglycerides are then surrounded with a protective protein coat (like rain gear) in order to be transported to the liver. These become large transporter molecules, the chylomicrons, which first go into the lymph circulation before entering the blood to go to the liver. VLDLs also carry some of the triglyceride molecules. Phospholipids and cholesterol are also incorporated into chylomicrons in order to get to the liver. After a fatty meal, the blood may be filled with chylomicrons, and the blood serum may have a milky appearance.

In the multifunctional liver, the chylomicrons are separated and the fats may be dismantled and reassembled into other needed fats. Lipids can also combine with proteins to make lipoproteins, with phosphate to make phospholipids, or with carbohydrates to form glycolipids. In the blood, free fatty acids, the active lipids for cell use, are bound to albumin, a protein. The other fats, such as cholesterol, are bound mainly to the high- and low-density lipoproteins. Each cell can take the triglycerides out of the lipoproteins and use the fatty acids for energy. Excess fat in the body is often stored in the fat cells. The adult human has a set number of fat cells, which enlarge to accommodate the increased triglyceride stores; an obese person’s fat cells may be many times larger than a thin person’s. These fat cells are formed at specific times of growth, such as infancy and adolescence. So later in life when we work to lose or gain weight, we are just shrinking or expanding our existing cells. And these fat cells are in a constant state of metabolism; they do not just sit there as many people think.

Functions
Lipids perform many life-supporting functions in each cell of our body. They are part of every cell membrane and every organ and tissue. The fatty acids keep our cells strong to protect against invasion by microorganisms or damage by chemicals. Fats are very important to our nervous system and in the manufacture of the steroid and sex hormones and the important hormonelike prostaglandins. Cholesterol is responsible for some of these functions that support the health of the brain, nervous system, liver, blood, and skin.

Beside the fact that fats add a lot of the flavor to the foods that many of us are used to and savor, such as buttery treats, gravies, and juicy meats, fats serve three primary functions in the body. They are first and foremost a ready energy source, contributing nine calories for every gram of fat used, more than 4,000 calories per pound of fat.

That’s a lot of potential energy we are carrying, both from dietary intake of those fatty foods and in the stored fat of our body. This stored fat helps give the body its curves and can be used for fuel during times of reduced food intake.

Fats in the body also act as a protective blanket shielding the organs from trauma and cold. The fat deposits surround and hold in place important organs such as the heart and kidneys. Fat below the skin helps prevent heat loss and protects against external temperature changes.

Third, as I have already said, the lipids are an integral part of the cell membranes. Every body cell and thus every tissue and organ is dependent on lipids in the body for its health. Also, fats are needed for absorption of vitamins A, D, E, and K, and by assisting in vitamin D absorption, they help calcium get into the body, especially to the bones and teeth.

Requirements, Deficiency, and Excess
There is no specific Recommended Daily Allowance (RDA) for dietary fats, though the National Academy of Science suggests at least 15–25 grams (that’s less than 10 percent of the fat in the average diet) of fats from foods, including some vegetable sources, to obtain sufficient amounts of our essential fatty acids. Though we could actually live on very little fat, meeting our minimum requirements is seldom difficult, since it is found in many protein and carbohydrate foods. Basically, our only dietary fat requirement is for the key essential fatty acids, linolenic (omega-3) and linoleic (omega-6), ranging from 2–5 percent of calorie intake. Our needs are based on many factors, and most people need a 2:1 ratio of omega-3 to omega-6 fatty acids. Whenever supplementing essential fatty acids, such as safflower, flaxseed, or canola oils, it is wise to take additional vitamin E (100–400 IU) to reduce potential oxidation of these polyunsaturated oils.

A general health recommendation is that our diet provide no more than 25–30 percent* of our total calories from fat nutrients, and that is for food intake in an amount just sufficient to maintain optimum weight, not to supply any excess body weight. Climate and body temperature are important factors in determining fat requirements. If we get cold easily, we may need more fat in our diet, provided our weight and thyroid are normal.

Since linoleic and linolenic acids are polyunsaturated fats available mainly in vegetable sources, such as corn, safflower, and soybean oils, as well as many nuts and seeds, it is conceivable that we could eat solely animal fats and still not get our needed amounts of essential fatty acids. Deficiency of vitamin F (essential fatty acids) can lead to dryness, scaliness, or eczema of the skin, as well as to reductions in the oil-soluble vitamins A, D, E, and K. Also, if there is deficient fat intake during growth periods, a retardation in the growing process may occur. Fortunately, however, fat deficiencies are not very common, though obtaining the right balance of fats, particularly of alpha-linolenic acid, given the standard diet is not easy, but very important.

In most Western cultures, as in American society, the real concern is over an excess intake of fat. The average daily diet (higher than needed for ideal weight and health) includes about 150 grams of fat, providing 1,350 calories, well over 40–50 percent of needed daily dietary calories. This is an increase over fat consumption earlier in the century, which averaged about 120 grams per day. And much of this is from the so-called “unhealthy” fats—meat and its saturated fats, hydrogenated oils, such as vegetable shortening, and foods fried in cooking oils. In the last 10–15 years, however, there has been a great deal of public education about the high-fat diet and, as a result, a small reduction in average fat intake has occurred. In the early 1970s, fat intake was about 160 grams per day; now it has dropped to under 150 grams.

An analysis of fat consumption of the typical North American’s diet was done by the Select Committee on Nutrition and Human Needs of the U.S. Senate. The reason for this study is the obvious role that dietary fat plays in disease. In 1977, they published their Dietary Goal for the United States, revealing that the average American consumed 42 percent of his or her calories from lipids, approximately 16 percent saturated fats, 19 percent monosaturated, and 7 percent polyunsaturated. To obtain a higher percentage of polyunsaturated fat and a lower percentage of fats in total, the Senate Select Committee has suggested the following:

• Reduce the consumption of red meats, organ meats, eggs, and dairy products in the diet.
• Choose low-fat protein sources, such as fish, turkey, chicken, and legumes (dried peas and beans).
• When consuming meats, use lean cuts and trim excess fats.
• Substitute skim and low-fat milk products for whole-fat dairy foods.
• Broil, bake, or boil foods instead of frying.
• Increase the consumption of fruits, vegetables, and whole grains in the diet. More long-range and specific goals* for our fat consumption include:
• Reduce dietary fat consumption from about 40 percent to 30 percent of calorie intake.
• Reduce saturated fats to about 10 percent of intake, with approximately equal amounts of monounsaturated and polyunsaturated fats—that is, more vegetable-source lipids.
• Reduce cholesterol intake to about 300 mg. per day.