Modes of action of lipid-lowering diets in man: studies of apolipoprotein B kinetics in relation to fat consumption and dietary fatty acid composition.

The mechanisms by which dietary fat influences fasting plasma lipid concentrations have been investigated in hyperlipidaemic subjects. The synthetic and fractional catabolic (FCR) rates of the apoprotein B (apo B) of very-low density (VLDL) and low-density (LDL) lipoproteins were measured using radioiodinated autologous lipoproteins. Reductions of LDL concentration in eight subjects during low-fat (25% of energy) diets were largely explained by diminished synthesis (-20%, P less than 0.02), and possibly also by an increased FCR (+15%, P = 0.05) of LDL, compared with observations made during a high-fat (45% of energy) diet of similar fatty acid composition. VLDL apo B synthesis and FCR were not significantly altered. When a diet rich in polyunsaturated fatty acids was exchanged for one high in saturated fatty acids (fat providing 45% of energy on both occasions) in four subjects, the synthetic rates of both VLDL apo B (-31%, P less than 0.02) and LDL apo B (-23%, P less than 0.10) were reduced while their FCRs were unchanged.