Daily 16:8 Versus Weekly 5:2 Intermittent Fasting for Weight Loss and Metabolic Health: A Randomized Controlled Trial

OBJECTIVE: This study compared the effects of 16:8 and 5:2 intermittent fasting on body weight, metabolic outcomes, and temporal response patterns in adults with overweight or obesity. METHODS: In this open-label randomized trial, 68 women with overweight or obesity were assigned to either a 16:8 regimen or a 5:2 regimen using a fasting-mimicking diet on fasting days for 4 weeks. Primary outcomes were changes in body weight and body composition; secondary outcomes included waist circumference, blood pressure, dietary intake, and glycemic metrics. RESULTS: Across both groups, body weight decreased by 2.7 kg (95% CI -2.9 to -2.4), fat mass by 1.7 kg (-1.9 to -1.5), and muscle mass by 0.6 kg (-0.7 to -0.4). Weight and fat mass reductions were greater over time in the 5:2 group than in the 16:8 group, whereas muscle mass changes were similar. Waist circumference and blood pressure decreased significantly, with no between-group differences. Both regimens reduced eating window duration, energy intake, mean and peak glucose levels, and time spent in hyperglycemia. CONCLUSIONS: Both regimens improved body weight and metabolic outcomes over 4 weeks. Despite similar overall effectiveness, the regimens exhibited distinct temporal response patterns, suggesting that temporal dynamics may inform individualized intermittent fasting strategies. TRIAL REGISTRATION: Clinical Research Information Service (cris.nih.go.kr) identifier: KCT0010806.