Diets of different fatty acid composition producing identical serum cholesterol levels in man

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Abstract
Because the cholesterol-raising effect of saturated fatty acids with 12 to 16 carbon atoms is twice as great as the cholesterol-depressing effect of polyunsaturated fatty acids, fats containing two parts of the latter to one of the former should have no effect on serum cholesterol concentration. This hypothesis was tested in 38 middle-aged, physically healthy, mentally retarded men. Two such test fats with different content of monoene fatty acids were used. They were incorporated as supplements into a diet in amounts providing about 25% of the total caloric intake. A third diet contained a supplement of the same caloric value but having one-third of the energy as test fat and two-thirds as carbohydrates. A fourth diet contained a supplement providing 25% of total caloric intake as carbohydrate, mainly sucrose. These four diets were fed in a Latin square design to four subgroups of men for periods of 4 weeks each. In a preliminary and a final period a diet containing an equivalent butter supplement was fed. The food intake of each individual was adjusted in order to maintain a constant body weight throughout the experiment. The four test diets gave practically identical serum cholesterol and phospholipid levels. These results show that the test fats can be isocalorically exchanged for each other, for monoene fatty acid glycerides, and for dietary carbohydrates (mainly sucrose) without producing any significant change of serum cholesterol or phospholipid concentration. As expected, the butter diet produced higher levels of serum cholesterol and phospholipids than those observed with the four test diets. The two test fats gave identical serum triglyceride levels. Substitution of carbohydrate for the test fats produced a marked increase of serum triglycerides roughly proportional to the increase in the carbohydrate content of the diet. Isocaloric substitution of butterfat for the test fats caused a significant increase of serum triglycerides that was, however, smaller than that produced by carbohydrates. The data of this experiment and previous observations in this laboratory indicate that the saturated fatty acids with fewer than 12 carbon atoms and stearic acid, which do not affect serum cholesterol, produce elevations of serum triglycerides. On the other hand, saturated fatty acids from 12 to 16 carbon atoms, which elevate serum cholesterol concentration, seem to have little effect on serum triglycerides.