Dietary oleic and palmitic acid exert similar effects on plasma lipids and lipoprotein metabolism in hamsters fed purified diets with low cholesterol but different quantities of fat.Asia Pac J Clin Nutr 1997; 6(1):26-30AP
The current study was designed to determine whether the transition from a low-fat (20% en) to a high-fat (40% en) diet through incremental increases in specific fatty acids (16:0 or 18:1) would exert a differential effect on plasma lipids and lipoprotein metabolism. Male Golden Syrian hamsters were fed purified diets in which the dietary fat (fatty acids) content was varied by blending different dietary oils. Animals were fed one of 5 purified diets: a low-fat control diet with 20% en fat; two diets with 30%en from fat; and two diets with 40% en from fat. In each case the extra fat was supplied either by oleic acid or palmitic acid. Dietary myristic (0 - 0.50% en) and linoleic acid (5.2 -5.9% en) were relatively constant across all diets, which contained a low level of cholesterol (~40 mg/1000 kcal). Diets were formulated so that protein, vitamins and minerals were constant per calorie. All animals were fed a fixed amount of calories for 6-8 week periods. Plasma lipids (n=15-20 per group) and lipoprotein cholesterol concentrations were determined following sequential ultracentrifugation, from individual animals (n=5-6 per group). Increasing dietary fat from 20% en to 30% en to 40% en, by increasing oleic acid (6.9% en to 16.5% en to 24.8% en respectively), did not affect total cholesterol (TC), triglyceride (TG) or lipoprotein cholesterol concentrations. Similarly, increasing dietary fat from 20% en to 30% en to 40% en, by increasing palmitic acid (6.6% en to 12.9% en to 21 % en) had no affect on plasma lipids or lipoprotein cholesterol. The similarity in plasma and lipoprotein cholesterol levels was further confirmed by kinetic studies (at 8 weeks) in which animals were injected simultaneously with either radiolabeled native LDL and methylated LDL or radiolabeled native LDL and HDL. Consistent with the similarities in circulating LDL-C concentrations, there was no difference in the clearance (ie fractional catabolic rates and half-lives) of LDL by either receptor-mediated or receptor-independent pathways. Similarly, in agreement with the similar HDL-C concentrations, no difference was observed in HDL fractional catabolic rates. Thus, if dietary myristic acid is low and linoleic acid is adequate and constant, dietary 16:0 and 18:1 can be readily interchanged, across a wide range of energies without compromising the plasma lipid profile in normocholesterolaemic animals consuming low-cholesterol diets. Whether this 16:0/18:1 equivalence is dependent on the relatively low levels of dietary cholesterol and/or adequate amounts of linoleic acid (~5 to 6% en) remains to be established.