Dietary Fat, Plasma Lipids, and Other CHD Risk Factors

BACKGROUND:

Although the consumption of trans-fatty acids or hydrogenated fat has consistently been shown to elevate concentrations of total and LDL cholesterol, the effects on HDL-c and Lp(a) are inconsistent, especially when the fats were consumed at moderate levels. In addition, little is known about the mechanisms by which trans-fatty acids increase total and LDL cholesterol levels or how they may alter the atherogenecity of lipoprotein subfractions. The study interventions employ commonly used hydrogenated fats with a wide range of trans-fatty acid levels (1.5-9.8 percent). The impact will be assessed within the guidelines currently recommended for individuals with moderately elevated plasma levels for which dietary modification is often the first approach to treatment. The results of the study may lead to improved public health recommendations concerning trans-fatty acid and hydrogenated fat intake.

DESIGN NARRATIVE:

Forty subjects (20 male, 20 female) ages 50 or older, with LDL cholesterol concentrations greater than 130 mg/dl were fed each of five diets for eight week periods. The baseline diet consisted of 36 percent of energy as fat (15 percent saturated, 15 percent monosaturated, 6 percent polyunsaturated) and 160 mg cholesterol/1000 kcal. The experimental diets contained 30 percent energy as fat, 2/3 of which was derived from each of the following: 1) unhydrogenated liquid soybean oil, 2) soybean oil margarine in tub form, 3) commercial shortening, and 4) butter in a randomized double blind, cross-over design. With the exception of the experimental fat, all other foods in the reduced fat diets were identical.

The study assessed the impact of consuming diets enriched in hydrogenated and other fats on a) plasma lipids and lipoprotein concentrations, b) apolipoproteins A-1 and B and Lp(a) concentrations, c) parameters related to HDL cholesterol [particle size, composition, subfraction distribution (HDL2 and HDL3, and HDL with and without A-II)], d) susceptibility of LDL to oxidation, e) activities of lecithin cholesterol acyltransferase (LCAT) and cholesterol ester transfer protein, and f) rates of endogenous cholesterol synthesis.