Caloric Restriction Chronically Impairs Metabolic Programming in Mice

Although obesity rates are rapidly rising, caloric restriction re-mains one of the few safe therapies. Here we tested the hypo-thesis that obesity-associated disorders are caused by increased adipose tissue as opposed to excess dietary lipids. Fat mass (FM) of lean C57B6 mice fed a high-fat diet (HFD; FMC mice) was “clamped ” to match the FM of mice maintained on a low-fat diet (standard diet [SD] mice). FMC mice displayed improved glucose and insulin tolerance as compared with ad libitum HFD mice (P, 0.001) or SD mice (P, 0.05). These improvements were associated with fewer signs of inflammation, consistent with the less-impaired metabolism. In follow-up studies, diet-induced obese mice were food restricted for 5 weeks to achieve FM levels identical with those of age-matched SD mice. Previously, obese mice exhibited improved glucose and insulin tolerance but showed markedly increased fasting-induced hyperphagia (P