Hypoadiponectinemia and decreased adiponectin gene expression in white adipose tissue (WAT) have been well observed in obese subjects and animal models. However, the mechanism for obesity-associated hypoadiponectinemia is still largely unknown. To investigate the regulatory role of energy intake, dietary fat, and adiposity in adiponectin gene expression and blood adiponectin level, a series of feeding regimens was employed to manipulate energy intake and dietary fat in obese-prone C57BL/6, genetically obese ob/ob, obese-resistant A/J and peroxisome proliferator-activated receptor-␣ gene knockout (PPAR␣ KO) mice. Adiponectin gene expression in WAT and circulating adiponectin levels were studied in these dietary intervention-treated mice. Our study showed that calorie restriction (CR) robustly increased adiponectin gene expression in epididymal fat and blood adiponectin levels in both low-fat (LF) and high-fat (HF) diet-fed C57BL/6 mice. Although HF pair-fed C57BL/6 mice received the same amount of calories as LF ad libitum-fed mice, HF diet clearly increased adiposity but showed no significant effects on adiponectin gene expression and blood adiponectin level. CR also significantly increased blood adiponectin levels in ob/ob and A/J mice. Neither CR nor HF feeding displayed any significant effect on blood adiponectin half-life in C57BL/6 mice. Interestingly, CR increased PPAR␣ expression in epididymal fat of C57BL/6 mice. Low levels of blood adiponectin and adiponectin gene expression in WAT were observed in PPAR␣ KO mice. PPAR␣ agonist treatment increased adiponectin mRNA levels in 3T3-L1 adipocytes. Furthermore, CR failed to increase adiponectin gene expression and blood adiponectin levels in PPAR␣ KO mice. Therefore, our study demonstrated that energy intake, not dietary fat, plays an important role in regulating adiponectin gene expression and blood adiponectin level. PPAR␣ mediates CR-enhanced adiponectin gene expression in WAT. obesity; adipocyte; calorie restriction ADIPONECTIN IS AN ADIPOCYTE-DERIVED HORMONE with insulinsensitizing function and plays an important role in maintaining energy homeostasis. Adiponectin gene expression in white adipose tissue (WAT) and blood concentrations are inversely associated with body mass index in humans (1,8,44). However, despite the close association of adiposity and hypoadiponectinemia, it is still not certain whether WAT expansion itself reduces adiponectin gene expression and adiponectin levels in circulation.The primary function of WAT is energy storage. Prolonged positive energy imbalance or excessive energy intake increases triglyceride accumulation in adipocytes and enlarges WAT mass. Therefore, calorie-enriched foods are generally blamed as the main cause of the obesity epidemic. In addition, high-fat (HF) diet has been widely used for inducing obesity in animal models that exhibit reduced adiponectin gene expression in WAT (3,10,25). This raises the question whether energy intake or dietary fat content controls adiponectin gene expression in WAT.Calorie restri...