Dietary restriction of saturated fat and cholesterol decreases HDL ApoA- I secretion

Abstract

We examined the mechanisms responsible for the decrease in HDL cholesterol (HDL-C) levels after the consumption of a diet low in total fat, saturated fat, and cholesterol. Twenty-one subjects with a mean age of 58±12 years were placed on a baseline isocaloric diet (15% protein, 49% carbohydrate, 36% fat, and 150 mg/1000 kcals of cholesterol) and then switched to an NCEP Step 2 diet (15% protein, 60% carbohydrate, 25% fat, and 45 mg/1000 kcals of cholesterol). After 6 or 24 weeks on each diet, subjects received a 15-hour primed-constant infusion of [5,5,5-2H3]-L-leucine. HDL apoA-I and apoA-II tracer curves were determined by gas chromatography-mass spectrometry and fitted to a monoexponential equation. Compared with the baseline diet, consumption of the Step 2 diet lowered HDL-C mean levels by 15% (1.03±0.23 to 0.88±0.16 mmol/L, P<0.001), apoA-I by 12% (1.25±0.15 to 1.10±0.13 g/L, P<0.001) and the TC/HDL-C ratio by 5% (0.145±0.04 to 0.137±0.03). No significant changes were observed in apoA-II levels and HDL particle size with diet. HDL apoA-I fractional catabolic rate did not change (0.219±0.052 to 0.220±0.043 pools/day, P=0.91) but HDL apoA-I secretion rate decreased by 8% (12.26±3.07 to 10.84±2.11 mg · kg-1 · day-1, P=0.03) during consumption of the Step 2 diet. There was no effect of diet on apoA-II fractional catabolic rate or secretion rate. Our results indicate that the decrease in HDL-C and apoA-I levels during the isocaloric consumption of a Step 2 diet paralleled the reductions in apoA-I secretion rate.