Negative regulation of leptin by chronic high-glycemic index starch diet

The response of plasma leptin to a high-glycemic index (high-GI) starch die t after a short (3 weeks) and prolonged (12 weeks) period was determined in Sprague-Dawley rats. Age-matched rats were fed an identical isocaloric die t except that the carbohydrates were from either mung bean starch (low-GI) or waxy cornstarch (high-GI). After a single test meal of the high-GI starc h diet, postprandial plasma glucose (P < .05) and insulin (P < .01) peaks a nd plasma glucose (P < .014) and insulin (P < .05) areas were higher versus the low-GI starch diet (n = 8 per group). Other age-matched control rats w ere fed the same diets for a longer period. After 3 weeks, ob mRNA levels w ere decreased by 50% (P < .005) in the epididymal adipose tissue of high-GI -fed rats versus low-GI-fed rats, without a significant decrease in plasma leptin. After 12 weeks of the high-GI starch diet, both plasma leptin and o b mRNA were decreased by 34% (P < .005) and 41% (P < .05), respectively, co mpared with the low-GI diet. Both relative epididymal adipose tissue weight (adjusted per 100 g body weight) and total fat mass, as measured by dual-e nergy x-ray absorptiometry (DEXA), were unchanged by the high-GI starch die t. Basal nonfasting plasma insulin, glucose, and triglycerides were not alt ered by the high-Gl starch diet, whereas free fatty acids were significantl y elevated and associated with a trend (P < .13) for increased plasma free glycerol, Plasma leptin levels were negatively correlated with free fatty a cid levels (r = .56, P < .05). Despite low leptin, rats fed on the high-GI diet did not increase their food intake, suggesting increased leptin sensit ivity. These findings might precede weight gain and the increase in fat mas s. Chronic nutritional factors might alter plasma leptin via several overla pping factors independently of energy intake. Copyright (C) 2000 by W.B. Sa unders Company.