A HIGH GLYCEMIC INDEX STARCH DIET AFFECTS LIPID STORAGE-RELATED ENZYMES IN NORMAL AND TO A LESSER EXTENT IN DIABETIC RATS

The aim of this study was to evaluate the chronic effects of a high (w axy corn) vs. a low (mung beans) glycemic index starch diet on the lip ogenic enzymes, fatty acid synthase (FAS) and lipoprotein lipase (LPL) . Normal and diabetic (streptozotocin-injected on d 2 of life) male Sp rague-Dawley rats consumed a diet containing 575 g/kg carbohydrates ei ther as waxy cornstarch (WCS) or as mung bean starch (MBS). After 3 wk , neither body weights nor relative epididymal fat pad weights differe d. In diabetic rats, the WCS diet induced high basal plasma insulin le vels. Plasma triglycerides were not significantly affected by diet in either normal or diabetic rats. Adipose tissue and liver LPL activitie s were not modified by the type of starch in the diet. In normal rats, FAS activity and gene expression in epididymal adipose tissue but not in liver were greater in rats consuming the WCS diet than in those co nsuming MBS. To evaluate the implication of insulin in this regulation , two genes regulated by insulin [GLUT4 and phosphoenolpyruvate carbox ykinase (PEPCK)] were also studied. The high glycemic index WCS diet c ompared with the low glycemic index MBS diet resulted in lower hepatic PEPCK mRNA in both normal and diabetic rats. Normal, but not diabetic rats fed WCS had greater GLUT4 gene expression in adipocytes than did those fed MBS. We conclude that the total replacement of 575 g/kg low glycemic index starch by a high glycemic index starch for 3 wk caused the following in normal rats: 1) high FAS activity and mRNA in adipos e tissue but not in liver and 2) high GLUT4 gene expression in adipose tissue. In both normal and diabetic rats this same diet resulted in l ower hepatic PEPCK mRNA. Therefore, high glycemic index starch diet is implicated in stimulating FAS activity and lipogenesis and might have undesirable long-term metabolic effects.