PURPOSE : Intermittent fasting and endurance exercise are among the most common health-promoting methods. The purpose of this study was to analyze the health-promoting effects of simultaneous treatment with intermittent fasting and endurance exercise in rats. The specific goals are as follows. Both intermittent fasting and exercise are known to promote health. But this is only when applied appropriately based on the application goals. When intermittent fasting and endurance exercise are treated together in the same amount or intensity, are the health-promoting effects produced at the same level as the effects of individual treatments? Does it show more effect than one method alone? Or is it inhibiting some of the health-promoting effects because of the stress caused by the concurrent treatment? This study seeks to address these questions. This study provides information on dietary intake settings and physical activity settings when developing health promotion programs for people of normal weight based on a combination of diet (intermittent fasting) and exercise (endurance exercise).METHODS : 16 6-week-old male SD rats were used as the research objects. Randomly divided into 4 groups. They are Sed (Sedentary), IF, Ex (Exercise), and IFEx. 4 per group. Feed with normal food. Free access to water. The room temperature and air humidity were controlled at 24°C and 50%, respectively. 12h light and 12h dark cycle. Body weight and food intake were recorded daily. The Sed group does not impose any intervention methods. IF group and IFEx group fast for 24 hours on Wednesdays and Saturdays. Ex group and IFEx group do 1 hour of moderate-intensity treadmill exercise on Mondays, Tuesdays, Thursdays, and Fridays. The experiment lasted 8 weeks. Experimental animals were dissected 23 hours after the last exercise. Epididymis fat, Sol (soleus muscle), TA (tibialis anterior muscle), EDL (extensor digitorum longus muscle), and Gas (gastrocnemius muscle) were isolated. These tissues were weighed and placed in liquid nitrogen refrigeration. Then store in -80°C refrigerator. Muscle atrophy-related protein p-Foxo1, MuRF-1, and MaFbx; ETC(Electron Transport Chain) enzymes NADH, COX1, COX4, and ATPsyn were determined by Western blotting. The mean and standard error (Mean±SE) of each group were calculated using SPSS 23.0 statistical software. One-way ANOVA was used to compare differences between groups. If the results were statistically different, then Tukey's post hoc test was performed. The significance level of difference was set at p < 0.05. RESULTS : 1. IF effectively reduced body weight and decreased visceral fat mass. IF preserved muscle mass well. The expression of muscle atrophy-related proteins p-Foxo1, MuRF-1 and MaFbx did not change significantly. IF decreased the expression of ETC enzyme ATPsyn. And there was no significant difference in ETC enzyme NADH, COX1 and COX4, but all showed a decreasing trend. 2. Ex effectively reduced body weight and decreased visceral fat. Ex preserved muscle mass well. The expression of muscle atrophy-related proteins p-Foxo1, MuRF-1 and MaFbx did not change significantly. There was no significant difference in the expression of ETC enzymes NADH, COX1, COX4 and ATPsyn, but all showed a tendency to increase. And the expression level of ETC enzyme was higher than that of IF and IFEx groups. 3. IFEx effectively reduced body weight and decreased visceral fat. And the effect is the highest among the three groups. IFEx decreased the amounts of TA, Gas and EDL, but did not affect Sol. IFEx increased the expression of muscle atrophy-related proteins p-Foxo1 and MaFbx in EDL. Expressions of ETC enzymes NADH and COX1 were similar to those in the IF group and lower than those in the Ex group. Expression of the ETC enzyme ATPsyn was higher than in the IF group.CONCLUSIONS: 1. Intermittent fasting is effective for weight loss, visceral fat reduction, and muscle mass maintenance. However, intermittent fasting inhibited mitochondrial oxidative phosphorylation. 2. Endurance exercise is effective for weight loss, visceral fat reduction, and muscle mass maintenance. Although endurance exercise did not significantly improve mitochondrial oxidative phosphorylation, it was the most beneficial of the three methods. 3. The combination of intermittent fasting and endurance exercise was the most effective of the three methods for weight loss and visceral fat reduction, but caused muscle atrophy. It has the effect of inhibiting oxidative phosphorylation. This shows that the combination of intermittent fasting and endurance exercise is not good for health. To improve the health, it need to reduce the amount of intermittent fasting and/or endurance exercise.Keywords: Intermittent Fasting, Endurance Exercise, Muscle Mass, Mitochondria