Plasma lipid changes in young adult couples consuming polyunsaturated meats and dairy products

Twenty-five young couples consumed either a saturated or polyunsaturated fat diet for a 20-week period. The polyunsaturated beef, lamb and dairy products, high in linoleic acid, were produced by feeding ruminant animals "protected lipid" feeds which prevent hydrogenation of fats in the rumen. The experimental design provided for four dietary groups: A) saturated diet for 20 weeks; B) polyunsaturated diet for 20 weeks; C) saturated diet for 10 weeks then polyunsaturated diet for 10 weeks; and D) polyunsaturated for 10 weeks then saturated diet for 10 weeks. Polyunsaturated-to-saturated ratios (linoleic: total saturated fatty acids) for the diets were: prestudy, 0.43-0.56; saturated 0.11-0.14; polyunsaturated, 0.56-0.62. Factors other than diet that appeared to affect cholesterol responses were carefully considered. During the initial 3 weeks (regimentation period) plasma cholesterol concentration decreased in all groups irrespective of diet. This was followed by two experimental periods in which the effects of the prescribed diets were readily apparent (response periods I and II). The final 4 weeks of the study were characterized by diminishing compliance with the dietary discipline (abatement period). Subjects in each group (A,B,C,D) were subdivided into high and low on a basis of each group's initial median cholesterol level. Those in the high subgroups were very responsive to dietary changes whereas those in the low subgroups were not. Combined responses of high subjects were: polyunsaturated diet, -10.7 mg/dl (P less than 0.025), saturated diet, d8 mg/dl (P less than 0.05). Combined difference between saturated and polyunsaturated diets was 18.5 mg/dl or approximately a 10% cholesterol difference between the experimental polyunsaturated and saturated diets.