Obese mice on a high‐fat alternate‐day fasting regimen lose weight and improve glucose tolerance

Alternate‐day fasting (ADF) causes body weight (BW) loss in humans and rodents. However, it is not clear that ADF while maintaining a high‐fat (HF) diet results in weight loss and the accompanying improvement in control of circulating glucose. We tested the hypotheses that a high‐fat ADF protocol in obese mice would result in (i) BW loss, (ii) improved glucose control, (iii) fluctuating phenotypes on ‘fasted’ days when compared to ‘fed’ days and (iv) induction of torpor on ‘fasted days’. We evaluated the physiological effects of ADF in diet‐induced obese mice for BW, heart rate (HR), body temperature (T_b), glucose tolerance, insulin responsiveness, blood parameters (leptin, insulin, free fatty acids) and hepatic gene expression. Diet‐induced obese male C57BL/6J mice lost one‐third of their pre‐diet BW while on an ADF diet for 10 weeks consisting of HF food. The ADF protocol improved glucose tolerance and insulin sensitivity, although mice on a fast day were less glucose tolerant than the same mice on a fed day. ADF mice on a fast day had low circulating insulin, but had an enhanced response to an insulin‐assisted glucose tolerance test, suggesting the impaired glucose tolerance may be a result of insufficient insulin production. On fed days, ADF mice were the warmest, had a high HR and displayed hepatic gene expression and circulating leptin that closely mimicked that of mice fed an ad lib HF diet. ADF mice never entered torpor as assessed by HR and T_b. However, on fast days, they were the coolest, had the slowest HR, and displayed hepatic gene expression and circulating leptin that closely mimicked that of Chow‐Fed mice. Collectively, the ADF regimen with a HF diet in obese mice results in weight loss, improved blood glucose control, and daily fluctuations in selected physiological and biochemical parameters in the mouse.