The effect of time-restricted feeding program on body composition, insulin sensitivity and fat oxidation in recreationally active men

Time-restricted feeding (TRF) is the most preferred intermittent fasting model in which the feeding window of individuals is limited to certain times of the day and the fasting window is at least 12 hours.. The aim of this study was to determine the effect of a 6-week TRF program on body composition, insulin sensitivity, fat oxidation at rest and during exercise in active men. Thirty-one recreationally active male volunteers between the ages of 18-39, healthy, exercising at least 3 days a week for at least 1 year participated in the study. Participants were randomly assigned to the TRF (n=14) or control (n=17) group. The TRF group followed the 16:8 program for 6 weeks, while the control group was asked not to change their current eating habits. Body composition, resting metabolic rate and fat oxidation during submaximal exercise were measured before and after the 6-week program. In addition, blood samples were taken from the participants at the beginning and at the end of the study after a 12-hour fasting period. After determining that the data were normally distributed, a two-way repeated measures (group × time) analysis of variance (ANOVA) was used to examine the differences between and within groups before and after TRF application. Body weight (p=0.002; partial eta squared (p2) =0.280), muscle mass (p=0.015; p2=0.20), lean body mass (p=0.015; p2=0.19) and fat mass (p=0.017; p2=0.18) decreased significantly after 6 weeks of TRF program. Group×time interactions of all these variables were also statistically significant (p<0.05). These findings show that the changes in these variables in the groups within 6 weeks are statistically different. Repeated measures ANOVA results showed that there was no significant change in resting metabolic rate and carbohydrate oxidation between groups and over time (p>0.05). The decrease in resting respiratory exchange ratio (RER) (p=0.014; p2=0.19) and increase in resting fat oxidation (p=0.006; p2=0.23) were statistically significant in terms of group×time interaction. The 6-week TRF program did not significantly change fat and carbohydrate oxidation during exercise, RER during exercise and blood parameters related to metabolism (p>0.05). In conclusion, the 6-week TRF program improves body composition by reducing fat mass and body weight in young healthy men, while improving substrate oxidation at rest. Its effect on substrate oxidation during exercise is limited.