[Comparison of intermittent fasting and exercise on skeletal muscle autophagy activation and fat reduction]

To observe the effect of weight control of intermittent fasting in different time course (14 d, 28 d)and explore its effect on skeletal muscle mass and autophagy.

Sixty SD rats (male) were randomly divided into sedentary group (Sed), intermittent fasting group (InF) and exercise group (Exe), 20 rats of each group, intervention duration is 14 d and 28 d. Animals of InF group were fasted every other day, animals of Exe group underwent aerobic exercise on treadmill, the weight was recorded every week. The body fat mass was recorded by DEXA and then the fat mass index was calculated. The wet weight of bilateral soleus muscle was weighed and wet weight index was calculated. Immunofluorescence was used to detect laminin and light chain 3 (LC3), which reflect muscle fiber cross-sectional area and autophagosome respectively. Transmission electron microscopy was used to observe the number and morphology of autophagosomes. The expression levels of autophagy related proteins Unc-51 like kinase 1 (ULK1), LC3, sequestosome1 protein (p62), AMP activated protein kinase (AMPKα) and p-AMPKα (Thr172) were detected by Western blot.

① From the 7th day of intervention, the body weight of rats in InF and Exe groups was significantly lower than that in Sed group, and the body weight of InF group was significantly lower than that in Exe group (P＜0.01). After 28 days of intervention, the fat mass index in InF and Exe groups was significantly lower than that in Sed group, the fat mass index of InF group was significantly lower than that in Exe group (P＜0.05).② After 28 days of intervention, the cross-sectional of muscle fibers in Exe group was significantly larger than that in Sed and InF groups (P＜0.01). ③The expressions of AMPKα, p-AMPKα (Thr172) and ULK1 in InF and Exe groups were significantly higher than those in Sed group (P＜0.05). However, at 14 days, only InF group showed the increase of LC3-II/LC3-I ratio and the decrease of p62 level (P＜0.05). The same indicators of Exe group were only significant changed at 28 d.

① Intermittent fasting is superior to exercise in controlling the growth of body weight and body fat in rats. ② In terms of skeletal muscle autophagy activation, the length of intervention required for intermittent fasting (14 days) is shorter than aerobic exercise (28 days).