The Effects of Certain Vegetable and Animal Fats on the Plasma Lipids of Humans

Abstract

Five apparently healthy male subjects, aged 33 to 41 years, consumed alternately mixed “free-choice” diets and homogenized “formula” diets. The latter, whose composition was accurately known, varied both in cholesterol content and in the amount and type of fat. Blood samples were taken throughout the study and the plasma analyzed for total and free cholesterol and phospholipid. Diets containing vegetable fat, comprising either 28.4 or 58.5% of total calories, with or without supplementary cholesterol, led to decreases of similar magnitude in plasma lipid levels relative to the levels found on the antecedent mixed “free-choice” diets. When animal fat, in the form of butter, was given to provide 58.5% of calories, there was an actual increase in lipid levels on the 4th and 7th days, followed by a return to a level slightly below that recorded at the beginning of this dietary period. Under the conditions of this study, there was a highly significant statistical difference between the effects of vegetable fat and animal fat on the blood lipids. A hypothesis has been presented to explain why a high dietary level of vegetable fat in a non-vegetarian diet of mixed food-stuffs causes an increase in plasma lipids whereas it has no such effect when included in a homogenized simple formula diet as the sole source of fat.