The Effect of Partial Hydrogenation of Dietary Fats, of the Ratio of Polyunsaturated to Saturated Fatty Acids, and of Dietary Cholesterol upon Plasma Lipids in Man*

The effect of alterations in dietary fat on the se-rum cholesterol level has been extensively studied during recent years. Numerous investigations have shown reductions in the serum lipid level of man after the dietary substitution of many vege-table oils for common animal fats or certain tropi-cal oils such as coconut oil (1-11). The relatively high degree of saturation of coconut oil and fats of animal origin has been associated with their cho-lesterol-elevating effect (8-12) and has led to the concept that saturated fatty acids per se are hyper-cholesterolemic (13). In this regard, Keys, An-derson, and Grande (12) reported that saturated fatty acids were approximately twice as active in raising serum cholesterol as polyunsaturated fatty acids were in reducing it. A reduction in the total unsaturation of the dietary fat, as measured by iodine value, has been reported to elevate serum cholesterol (9). Jolliffe (13) proposed that the effect of dietary fats on the serum cholesterol con-centration was a function of their ratio of polyun-saturated to saturated fatty acids (P/S). Al-though this concept that saturated fatty acids, or dietary fats with low P/S ratios, are hypercholes-terolemic is widely accepted, it has not been uni-formly demonstrated. Hashim, Arteaga, and Van Itallie ( 14), for instance, reported that a tri-glyceride consisting of saturated fatty acids with chain lengths ranging from 6 to 12 carbon atoms was hypocholesterolemic relative to dietary butter-fat. In an earlier study, Hashim, Clancy, Heg-sted, and Stare (15) observed that formula diets containing safflower oil or an equal mixture o