The role of dietary polyunsaturated fat in lowering blood cholesterol in man.

IT HAS BEEN nearly a quarter of a century since Keys and coworkers (see Refs. 1-3 and the pertinent references therein) demonstrated a statistically significant relationship between the death rate from coronary heart disease (CHD), plasma cholesterol levels, and the proportion of calories derived from total dietary fat. In these pioneer studies, it was shown that a Cape Town population which consumed foods rich in fat had a higher serum cholesterol level than a Bantu tribe which consumed less fat. Following these observations, there were a number of experimental studies in the mid-1950's in patients 1 " 7 and animals'*"" which showed that the feeding of saturated fat led to an elevation of plasma cholesterol, whereas polyunsaturated fats produced a decrease. The strong correlation between elevated plasma cholesterol levels and CHD led to several clinical trials which attempted to relate the consumption of the type of dietary fat and the course of the disease. 12 " 15 Although the overall results of these trials were inconclusive, many of the participants had prior CHD and were less likely to be helped by dietary modification. 1 " Nonetheless, based on epidemiological evidence and animal experiments, the American Heart Association, 17 the American Health Foundation, 1 " the Food and Nutrition Board of the National Research Council and the American Medical Association,'" and the Royal College of Physicians of London and the British Cardiac Society 2 " all have recommended changes in the diet which include a reduction of the total consumption of fat and cholesterol and the substitution of polyunsaturated for saturated fat. It is possible that one of the reasons for