For a long time, many medical authorities (including the American Heart Association until very recently) recommended substituting polyunsaturated fats in the diet for saturated fats. This is because of the belief that, since polyunsaturated fats reduce serum cholesterol levels, they reduce the risk of heart attack. The findings of several large studies now indicate otherwise.
It is true that polyunsaturated fats can reduce serum cholesterol levels to a small degree, but studies have shown that heart attack deaths are not lowered. Not only that, but it appears that cancer deaths are increased in patients with diets high in polyunsaturated fats. New understanding about the biochemistry of fat production and destruction provides a theoretical framework for explaining these otherwise puzzling findings.
In polyunsaturated fats, there are double bonds between some of the carbon atoms, whereas saturated fats do not have double bonds to act as chemical reaction sites. Polyunsaturated fats are much more susceptible to autoxidation, when oxygen or its chemical equivalents, without enzymatic control, directly attack the double bond sites and form oxidized fats called organic peroxides. This is the same chemical process that produces what are commonly called rancid (peroxidized) fats.
Peroxidized fats are highly toxic, mutagenic, and carcinogenic. Upon further breakdown they form free radicals—highly chemically reactive molecules with unpaired electrons. Free radicals are strongly implicated as causative agents in aging, cardiovascular disease, cancer, arthritis, cataracts, senility, plus a whole host of other conditions, including such lowly ones as bruises and dandruff.
Dr. Denham Harman of the University of Nebraska, the originator of the free radical theory of aging in the late 1950s, calls free radicals "internal radiation." That is a very good description of them because radiation sickness is the result of free radicals created by external radiation.
Dr. Harman fed polyunsaturated fatty acids to one group of rats and saturated fats of the same caloric content to another group. On a learning task, the rats fed polyunsaturated fats performed substantially less well than the other group in a period of time that was short compared to the rats' life span. The ease with which polyunsaturated fats are autoxidized is the most probable explanation for this strange phenomenon. When autoxidized (rancid) fats break down to yield free radicals, they can damage other fats, DNA, RNA, and proteins in the surrounding tissues. Since the brain contains far more polyunsaturated fats than does any other body tissue, it is far more susceptible to free radical damage.
Our bodies contain a complex system of protective enzymes and antioxidants—substances that react with the free radicals, converting them to less-harmful products. (Common antioxidants include vitamins A, E, C, B-1, B-5, B-6, PABA, the amino acid cysteine, the minerals zinc and selenium, and the synthetics BHT, BHA, propyl gallate, TBHQ, and DMSO.) For example, the brain has two special vitamin C pumps—one in the blood-brain barrier (the selective membrane surrounding the brain and spinal cord) and one in each nerve cell membrane—which keep the concentration of vitamin C inside brain cells 100 times higher than in the blood! And during a heart attack, white blood cells carry vitamin C from other parts of the body to the injured heart, even when the other areas have to be depleted of their vitamin C.
Free radicals are a necessary part of certain processes, such as the metabolism of food. But without free-radical-control enzymes, such as superoxide dismutase and glutathione peroxidase, and the natural antioxidants mentioned above, we would quickly die. In fact, all air-breathing organisms on this planet have very nearly the same control enzymes and antioxidants, although in varying proportions and amounts. Radiodurans, a bacteria that lives inside operating nuclear reactors, contains the highest levels of these protective antioxidant enzymes yet observed.
Cholesterol itself is an antioxidant. We think that the increases in serum cholesterol seen in some people is a bodily response to an increasing free radical load. It is interesting to note that some antioxidants taken singly in large doses, such as vitamins C and B-6, can reduce serum cholesterol by up to 35 percent or so. In our personal observations, combinations of antioxidants can reduce serum cholesterol by up to 50 percent.
Scientists now know that blood clotting is controlled via free radical reactions. A substance called prostacyclin lines the walls in normal arteries and, by keeping platelets in the blood from aggregating, prevents abnormal blood clotting (clots only form in a healthy artery when a hole is torn in it). Free radicals, however, produced in the breakdown of autoxidized (rancid) fats, can interfere with the normal productions of prostacyclin, resulting in abnormal clot formation and hence in cardiovascular problems.
Experiments have shown vitamin E to be an effective preventive of abnormal blood clots. Until recently, it was not understood how it could do this, but its basic biological function as a lipid (fat) antioxidant is the key. Vitamin E can protect the enzymatic prostacyclin-manufacturing apparatus from inhibition by free radical and organic peroxide damage.
Rather than substituting polyunsaturated fats for saturated fats—as long recommended—we have radically (no pun intended) increased our intake of antioxidant supplements. It is probably also safest to eat a diet with only a moderate level of fat. Do not eat a lot of polyunsaturated fats, especially without antioxidant supplements added to your diet. Even with the best of diets, the quantity of antioxidants you can get is limited. We purchase cooking oils that are not labeled as being high in polyunsaturates, and we always add BHT (a synthetic antioxidant) to it. Cooking oils often contain a high level of polyunsaturates and become autoxidized (rancid) very rapidly upon exposure to air. With added antioxidants, the shelf life may be many times as long.
As Dr. Harry Demopoulos of New York University's Medical School Department of Pathology has said, free radical pathology is as great a breakthrough in medicine as Pasteur's germ theory of disease. We plan to write more on this subject in future columns.
A list of scientific literature on this topic is available. Send a stamped, self-addressed envelope to this publication, referring to the date of this issue.
Sandy Shaw and Durk Pearson are consulting scientists, authors, and TV personalities. Copyright © 1981 by Sandy Shaw and Durk Pearson.