Dietary Factors Affecting the Level of Plasma Cholesterol in Humans: The Role of Fat

Abstract

Three dietary experiments have been performed in which 36, 37, and 49 male medical students and staff members participated as experimental subjects. In each study, everyone consumed the same homogeneous formula diet for eight days at which time they were divided into five groups. One group was maintained on the original diet for a further eight days and the others were given diets varying in respect of the level and nature of the fat moiety. Protein supplied 16.9% of total calories in all experimental rations. In the first experiment, 37 subjects ingested a diet providing 58.5% of calories as corn oil. During the initial period the average of the individual percentage decreases in plasma cholesterol was 32.0 (P = < 0.01). Those continuing on corn oil displayed a further insignificant decrease. The others, receiving diets high in beef dripping, chicken fat, lard, and butter showed average individual percentage increases of 11.7 (P = > 0.05), 12.7 (P = > 0.05), 15.4 (P = < 0.01), and 28.8 (P = < 0.01), respectively. In the second experiment, 49 subjects consumed a fat-free diet for eight days. The average individual percentage decrease in plasma cholesterol was 22.2 (P = < 0.01). Those continuing on the fat-free diet showed little further change. Those ingesting 20 and 60% of calories as corn oil showed further percentage decreases of 6.9 (P = > 0.05) and 15.2 (P = < 0.01), respectively. By contrast, those receiving diets providing 20 and 60%, of calories as butterfat showed respectively percentage increases of 6.6 (P = > 0.05) and 21.7 (P = < 0.01). In the third experiment, 36 subjects ingested for eight days a diet in which butterfat provided 60% of calories. The plasma cholesterol level remained essentially constant, and did not change significantly in those continuing on this diet for a further eight days. The composition of the fat moiety in the remaining groups in terms of per cent calories derived from butter-fat and corn oil respectively was: 45: 15; 30: 30; 15: 45; and 0: 60. The averages of the individual percentage decreases in plasma cholesterol values were, respectively, 3.9, 15.9, 27.1, and 32.0. Except for the lowest of these values all the changes are highly significant (P = < 0.01). In addition to other conclusions that may be drawn from this work, these studies reveal that (1) there is a factor (or are factors) in certain animal fats that acts to elevate plasma cholesterol levels, and (2) there is a factor (or are factors) in corn oil that acts to depress plasma cholesterol levels.

Polyunsaturated fatty acids, hyperlipidemia, and thrombosis.

“…About the same time, it was shown that the addition of polyunsaturated fat to a fat-free diet resulted in a reduction in plasma cholesterol levels, which was of the same magnitude as the rise observed when saturated fats were added. 37 The possibility that hypercholesterolemia resulted from EFA deficiency was discounted when it was shown that a fish oil high in co-3 polyunsaturates but low in linoleic acid effectively reduced plasma cholesterol levels.…”

Interaction of dietary cholesterol and triglycerides in the regulation of hepatic low density lipoprotein transport in the hamster.

“…It has long been recognized that the substitution of polyunsaturated fat for saturated triglycerides in the diet results in a reduction in plasma cholesterol levels (1)(2)(3)(4). Although the mechanism(s) responsible for this effect remains poorly understood, the relationship between various dietary lipids and plasma cholesterol levels in man has been studied in considerable detail (5)(6)(7)(8)(9).…”

The Interrelated Effects of Dietary Cholesterol and Fat upon Human Serum Lipid Levels *

“…Another factor is the fatty acid composition of the dietary fat. The substitution of polyunsaturated fat for saturated fat in the human diet generally has led to a lowering of serum cholesterol levels (13)(14)(15)(16)(17)(18). Most investigators who have altered dietary fat composition by substituting polyunsaturated for saturated fat have used either cholesterol-free formula diets or diets with reduced cholesterol content.…”