Fructose, High-fat Diet = Obesity?

GAINESVILLE, Fla.—Data from a recent study published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology indicated chronic fructose consumption induced leptin resistance, which accelerated high fat-induced obesity (DOI:10.1152/ajpregu.00195.2008). Sprague-Dawley rats were fed a fructose-free control or a 60-percent fructose diet for six months and then tested for leptin resistance. Half of the rats in each group were then switched to a high-fat diet for two weeks, while the other half continued on their respective diets. Chronic fructose consumption caused leptin resistance while serum leptin levels, weight and adiposity were the same as in control rats that were leptin-responsive. Intraperitoneal leptin injections reduced 24-hour food intake in the fructose-free group (P=0.02), but had no effect in the fructose-fed rats (P=0.9). Absence of anorexic response to intraperitoneal leptin injection was associated with a 25.7-percent decrease in hypothalamic signal transducer and activator of transcription 3 (STAT3) phosphorylation in the high-fructose fed rats compared with controls (P=0.015). Subsequent exposure of the fructose-mediated leptin-resistant rats to a high-fat diet lead to exacerbated weight gain compared with correspondingly fed leptin-responsive animals that were pre-treated with the fructose-free diet.