HUMAN FATTY-ACID SYNTHESIS IS STIMULATED BY A EUCALORIC LOW-FAT, HIGH-CARBOHYDRATE DIET

A new experimental approach was used to determine whether a eucaloric, low fat, high carbohydrate diet increases fatty acid synthesis. Norma l volunteers consumed low fat liquid formula diets (10% of calories as fat and 75% as glucose polymers, n = 7) or high fat diets (40% of cal ories as fat and 45% as glucose polymers, n = 3) for 25 d. The fatty a cid composition of each diet was matched to the composition of each su bject's adipose tissue and compared with the composition of VLDL trigl yceride. By day 10, VLDL triglyceride was markedly enriched in palmita te and deficient in linoleate in all subjects on the low fat diet. New ly synthesized fatty acids accounted for 44+/-10% of the VLDL triglyce ride. Mass isotopomer distribution analysis of palmitate labeled with intravenously infused C-13-acetate confirmed that increased palmitate synthesis was the likely cause for the accumulation of triglyceride pa lmitate and ''dilution'' of linoleate. In contrast, there was minimal fatty acid synthesis on the high fat diet. Thus, the dietary substitut ion of carbohydrate for fat stimulated fatty acid synthesis and the pl asma accumulation of palmitate-enriched, linoleate-deficient triglycer ide. Such changes could have adverse effects on the cardiovascular sys tem.