INFLUENCE OF LINOLEIC-ACID ON DESATURATION AND UPTAKE OF DEUTERIUM-LABELED PALMITIC AND STEARIC ACIDS IN HUMANS

Objectives of this study were to investigate the desaturation of stear ic acid (18:0) and palmitic acid (16:0), to determine if differences i n their metabolism provide a reasonable explanation for differences in their effect on serum cholesterol levels, and to investigate the affe ct of linoleic acid on DELTA9-desaturase products in man. Deuterium-la beled 16:0 and 18:0 were used to follow the metabolism of these fatty acids in young adult male subjects that were pre-fed diets containing two different levels of linoleic acid. Results indicate that absorptio n of 16:0 and 18:0 was similar when all components of the mixture used to formulate the deuterated fat mixture were kept above the melting p oint of tristearin. The percent of 18:0 desaturated to 9c-18:1 was hig her than the percent of 16:0 desaturated to 9c-16:1 (9.2% vs. 3.9%). T he subject-to-subject variability suggests that differences in ability to desaturate saturated fatty acids may be related to the variability observed in response of serum cholesterol levels to dietary saturated fatty acids. Data for the distribution of 16:0 and 18:0 between triac ylglycerol and phosphatidylcholine (PC) was markedly different. Based on PC data, phospholipid acyltransferase selectivity was about 2-fold higher for 18:0 than for 16:0. A 2-fold difference in the linoleic aci d content of the pre-fed diets had little influence on desaturation or distribution of 16:0 and 18:0 between plasma lipid classes. A deuteri um isotope effect was estimated to reduce DELTA9-desaturase enzyme act ivity by 30-50%.