Intermittent fasting and body Composition: Insights from the Iranian National obesity registry (IRNOR)

Background

The global rise of adiposity has increased interest in novel dietary approaches such as 5:2 intermittent fasting (IF) for health management. This study aimed to assess the impact of a 12-week 5:2 IF on both traditional and novel body composition metrics in individuals with overweight and obesity.

Methods

Data for this12-week longitudinal cohort study was extracted from the electronic database of the Iranian National Obesity Registry (IRNOR). According to data provided by IRNOR, adults with overweight or obesity were compared based on adherence to either 5:2 IF or a daily calorie restriction (CR) program. The 5:2 IF group consumed 500–600 kcal on fasting days and an isocaloric diet on non-fasting days, while the CR group reduced their calorie intake by 500–1000 kcal per day.

Results

A total of 102 participants (mean age 36.75 ± 12.25 years) were included. Over 12 weeks, both groups experienced significant reductions in weight, body circumference, and fat metrics, including visceral fat area (P < 0.05). The IF group, despite a non-significant smaller reduction in total calorie intake, achieved 1 kg greater weight loss than the CR group (−525.33 ± 831.01 vs. −506.23 ± 763.24, P = 0.08). In contrast to the CR group, the 5:2 IF did not show a significant reduction in body cell mass, fat free-mass index, extracellular water-to-total body water, and phase angle over time (P > 0.05).

Conclusions

The 5:2 IF may better preserve cellular structure and hydration balance, achieving clinically significant weight loss. Given its comparable efficacy, it may be a viable alternative. Further studies are required to confirm these findings.