Effects of Diet on VLDL Metabolism

It is well-known that diets high in simple carbohydrate increase hepatic secretion of VLDL. This carbohydrate induction of hypertriglyceridemia is the source of the current controversy regarding the optimal diet for subjects at high risk for cardiovascular disease. Some authors have demonstrated that the increased hepatic triacylglycerol secretion induced by high-carbohydrate diets was not accompanied by parallel increases in apo B-100 secretion. In other words, the consumption of low-fat, high-carbohydrate diets did not affect the number of particles but resulted in larger, more triacylgly-cerol-enriched VLDL particles.

Intake of saturated fat results in an increased secretion of the number of VLDL particles by the liver, whereas the opposite effect is observed with polyunsaturated fat. Of special note are the dramatic effects on VLDL production found following high intakes of n-3 fatty acids. These diets are associated with marked decreases in triacylglycerol secretion by mechanisms not fully understood. It

Table 3 Effects induced on the major lipoprotein fractions by different dietary components following isoenergetic replacement of saturated fatty acids

MUFA PUFA n-6 PUFA n-3 trans FA Simple carbohydrate Carbohydrate plus fiber

« equivalent effect; # concentration reduced; " concentration increased.

has been speculated that n-3 fatty acids may stimulate intracellular degradation of apo B in hepato-cytes. Dietary cholesterol, within the physiological range, appears to play a minor role in hepatic VLDL production.

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