Studies were carried out on the effects of polyunsaturated fats on lipid metabolism in 11 patients with hypertriglyceridemia. During cholesterol balance studies performed in eight patients, the feeding of polyunsaturated fats, as compaed with saturated fats, caused an increased excretion of endogenous neutral steroids acidic steroids, or both in most patients. Increases in steroid excretions were marked in some patients and generally exceeded the decrement of cholesterol in the plasma compartment. The finding of a greater excretion of fecal steroids on polyunsaturated fats in hypertriglyceridemic patients constrasts to the lack of change in sterol balance previously reported for patients with familial hypercholesterolemia; however, other workers have found that polyunsaturated fats also enhance steroid excretion in normal subjects. Reductions in plasma cholesterol during the feeding of polyunsaturated fats was seen in most patients, and these changes were usually associated with a decrease in concentration of plasma triglycerides. In fact, the degree of cholesterol lowering was closely correlated with the extent of triglyceride reduction. Therefore, in hypertriglyceridemic patients polyunsaturated fats may contribute to cholsterol reduction by changing the metabolism of triglycerides or very low density lipoproteins. The findings of changes in the metabolism of cholesterol, bile acids, and triglycerides in the patients studied suggests that polyunsaturated fats may cause a lowering of cholesterol through multiple mechanisms, and it seems unlikely that a single action can explain all the effects of these fats on the plasma lipids.
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