Palmitic acid effect on lipoprotein profiles and endogenous cholesterol synthesis or clearance in humans.

The effect of palmitic acid (C16:0) on serum lipoprotein cholesterol levels is debatable. If C16:0 is hypercholesterolaemic, then it may increase the endogenous synthesis or decrease clearance of cholesterol. Four diets were formulated to provide combinations of two levels of C16:0 in relation to two levels of PUFA. Healthy male subjects received each of the four diet treatments for 21 days, followed by washout periods of 21 days. On day 21 of each diet treatment, a fasting blood sample was drawn for lipoprotein determination and to provide a measure of the background level of deuterium. A priming dose of deuterium was consumed and a second blood sample obtained 24 hours after the first sample. Isotope Ratio Mass Spectrometry was used to determine the incorporation of deuterium into the newly synthesised cholesterol molecule, and fractional synthetic rates calculated. Serum total cholesterol and LDL-cholesterol was not significantly affected by the high level of C16:0 when diets also contained the high level of PUFA. There was no effect of C16:0 on HDL-cholesterol at either the high or low levels of intake. The fractional synthetic rates of cholesterol observed for each of the diet treatments did not significantly differ from one another, suggesting no relationship between the endogenous synthesis of cholesterol and diet C16:0 content. These results indicate that C16:0 had no effect on serum lipoprotein profiles in the presence of recommended intakes for PUFA, nor did it increase rates of cholesterol synthesis in healthy males.