Human fatty acid synthesis is reduced after the substitution of dietary starch for sugar

Using new nonisotopic and isotopic methods, we showed previously that fatty acid synthesis was markedly stimulated in weight-stable normal volunteers by a very-low-fat formula diet with 10% of energy as fat and 75% as short glucose polymers. In this study, we determined whether fatty acid synthesis was equally stimulated by a very-low-fat solid diet made with foods consumed typically. Four normal volunteers consumed the same very-low-fat formula diet for 25 d and then an isoenergetic solid food diet with 10% of energy as fat and 75% as starch, simple sugars, and fiber for 25 d. To measure fatty acid synthesis, the fatty acid compositions of the diets were matched to the composition of each subject's adipose tissue and compared with the composition of VLDL-triacylglycerol. In all subjects, the large increases in newly formed palmitate and decreases in linoleate in VLDL-triacylglycerol were quickly reversed by the solid food diet, and the fraction of de novo synthesized fatty acids in fasting VLDL-triacylglycerol decreased from 30-54% to 0-1%. In a second group of subjects, the stimulation of fatty acid synthesis by the formula diet with 75% glucose polymers was similarly reduced by a formula diet with amounts of fat, starch, and sugar chosen to mimic those of the solid food diet, but persisted after the addition of fiber or a diet with 75% sugar. In conclusion, an increase in fatty acid synthesis and palmitaterich, linoleate-poor VLDL-triacylglycerol induced by very-low-fat, high-sugar diets may be reduced by the substitution of dietary starch for sugar with potentially beneficial effects on cardiovascular health.

The metabolic and immunologic effects of short-term thalidomide treatment of patients infected with the human immunodeficiency virus

Thalidomide therapy has been shown to cause increases in body weight in patients with HIV and tuberculosis infections. To examine the nature of this weight gain and its immunological correlates in patients with HIV infection, we studied a cohort of 13 patients with minimally symptomatic HIV disease. Patients were admitted to the Rockefeller University General Clinical Research Center and maintained on strict isocaloric diets to achieve weight stabilization before a 14-day course of thalidomide treatment. Mean percentage weight increase was 3.6% on day 14 of thalidomide therapy (p = 0.002). Weight gain was associated with a reduction in mean daily urinary nitrogen excretion of 1.81 g (p = 0.017). Resting energy expenditure was unaffected by thalidomide. Body composition analysis suggested some extracellular fluid retention in the first week of thalidomide therapy, followed by an expansion of lean tissue mass during the second week. Remarkably, total lymphocyte counts and CD8+ T cell counts increased following treatment with the drug from 1578 +/- 185 to 2617 +/- 265 and from 938 +/- 146 to 1369 +/- 231, respectively. Modest increases in CD4+ T cell counts were also observed. Levels of circulating TNF-alpha were not elevated at baseline. A significant increase in mean plasma levels of soluble interleukin 2 receptor (sIL-2r), from 1918 +/- 250 to 3816 +/- 411 pg/ml (p = 0.0022), occurred in response to thalidomide, suggesting drug-induced immunological activation. In conclusion, thalidomide treatment of patients with HIV infection caused weight gain and lean tissue anabolism, even when caloric intake was kept constant. The nature of the association between thalidomide treatment-induced metabolic changes and the immunomodulatory effects of the drug has yet to be elucidated.

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. Normally 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 calories as fat and 45% as glucose polymers, n = 3) for 25 d. The fatty acid composition of each diet was matched to the composition of each subject's adipose tissue and compared with the composition of VLDL triglyceride. By day 10, VLDL triglyceride was markedly enriched in palmitate and deficient in linoleate in all subjects on the low fat diet. Newly synthesized fatty acids accounted for 44 +/- 10% of the VLDL triglyceride. Mass isotopomer distribution analysis of palmitate labeled with intravenously infused 13C-acetate confirmed that increased palmitate synthesis was the likely cause for the accumulation of triglyceride palmitate and "dilution" of linoleate. In contrast, there was minimal fatty acid synthesis on the high diet. Thus, the dietary substitution of carbohydrate for fat stimulated fatty acid synthesis and the plasma accumulation of palmitate-enriched, linoleate-deficient triglyceride. Such changes could have adverse effects on the cardiovascular system.