Effects of dietary carbohydrate and fat on plasma lipoproteins and apolipoproteins C-II and C-III in healthy men.

Effects of isocaloric changes in dietary fat and carbohydrate on plasma apolipoproteins (apo) C-II, C-III, and lipoproteins were assessed in nine healthy men. Carbohydrate and fat comprised 80% of total calories. After a 1-week basal diet (40% of calories from carbohydrate), the subjects received either a high (65% of calories) or low (15% of calories) carbohydrate diet for 3 weeks; subsequently the diets were switched, those initially on high carbohydrate going on to low carbohydrate, and vice versa, and the new diets were maintained for 3 weeks. ApoC-II, C-III, and triglycerides initially rose and then declined during the high carbohydrate diet period; high density lipoprotein cholesterol (HDL-C) decreased. Comparing results after 3 weeks of high carbohydrate diet to those after 3 weeks on low carbohydrate, we observed the following significant differences: 1) total plasma apoC-II and C-III were higher; the apoC-III/C-II ratio in very low density lipoproteins (VLDL) and in the lighter HDL subfraction (HDL2) was lower indicating net lipoprotein enrichment with apoC-II than with apoC-III; 2) unsialylated apoC-III0 comprised a higher percent of total VLDL apoC-III mass; 3) HDL2 and HDL2/HDL3 ratio were lower. Isocaloric changes in dietary carbohydrate and fat cause significant alterations in plasma levels of VLDL and HDL 2, the two major lipoproteins that transport apoC-III and apoC-II. Diet-induced changes in circulating apoC-III and C-II may, in part, play a role in regulation of plasma triglycerides in man.