Mechanisms mediating lipoprotein responses to diets with medium-chain triglyceride and lauric acid

Medium-chain triglycerides (MCT) are often used in specialized formula diet s or designer fats because of their special properties. Yet their influence on lipid metabolism is not completely understood. In this two-period cross -over study, the effects of MCT (8:0 + 10:0) in contrast to a similar satur ated fatty acid (12:0) were compared. Eighteen healthy women ate a baseline diet [polyunsaturated (PUFA)/saturated fat = 0.9] for 1 wk. Then, they con sumed test diets (PUFA/saturated fat = 0.2) for 4 wk. Monounsaturated fat a nd cholesterol were constant in baseline and treatment diets. MCT and 12:0, substituted for part of the PUFA, provided 14 energy (en)% of the test die ts. In comparison to the PUFA baseline diet, a 16% increase in mean serum l ow density lipoprotein (LDL)-cholesterol (C) on the 12:0 diet was accompani ed by a 21% decrease in mean receptor-mediated degradation of LDL by freshl y isolated mononuclear cells (MNC) in vitro. The MNC assay theoretically gi ves an indication of receptor-mediated degradation of LDL. In contrast, the MCT diet raised mean receptor-mediated degradation of LDL by 42%, a findin g out of line with the mean 11% increase in serum LDL-C. Perhaps MCT, by in creasing the rate of LDL-C production, overcame the rate of LDL-C clearance . The 12:0 diet enhanced some factors involved in reverse cholesterol trans port (e.g., high density lipoprotein fractions) while MCT had a different o r less pronounced effect. The overall effects of MCT on cholesterol metabol ism may or may not be desirable, whereas those of 12:0 appear largely undes irable as previously reported.