Effects of intermittent dieting with ad-libitum break periods on body composition and metabolic adaptation in physically inactive females with obesity: A randomized controlled trial

Abstract Background Continuous energy restriction (CER), the conventional weight-loss approach, often induces metabolic adaptation, mood disturbances, and poor long-term adherence. Intermittent dieting incorporating short breaks with ad libitum energy intake (INTB-AdI)—commonly termed “cheat meals”—have gained popularity in fitness communities as a potentially viable weight reduction strategy to attenuate these negative effects. This three-arm randomized controlled trial investigated the effects of INTB-AdI on body composition and metabolic adaptation, as compared to the CER approach. Methods 77 physically inactive females aged 18–35 years with obesity were randomized to 8 weeks of either: (1) CER with 70% energy balance daily (n = 26), (2) INTB-AdI with 70% energy balance on 5 days/week and 2 ad libitum feeding days/week (n = 26), or (3) control group (CON) maintaining habitual diet (n = 25). Physiological outcomes including body weight as the primary outcome were assessed at baseline, post- intervention, and at 3-month follow up. Results During the 8-week intervention, both CER and INTB-AdI resulted in significant weight loss compared to CON (CER: mean difference [95% Confidence Interval] − 2.8 kg [− 3.5 to − 2.0]), P < 0.001; INTB-AdI: −3.1 kg [− 3.9 to − 2.3], P < 0.001), with no differences between CER and INTB-AdI (P = 0.792). Resting metabolic rate (RMR) decreased significantly more in CER than in INTB-AdI (-69.9 kcal [− 114.3 to − 25.5], P < 0.001). Improvements in certain cardiometabolic health markers were observed in CER only. However, a small regain of body mass (P = 0.035) and fat mass (P = 0.006) 3-month post intervention was seen in INTB-AdI only. Conclusions Both 8-week CER and INTB-AdI interventions led to significant weight loss, with INTB-AdI attenuating the adaptive reduction in RMR more effectively than CER. However, INTB-AdI did not produce significant improvements in cardiometabolic markers, and its efficacy for post-diet weight maintenance remains uncertain. Further research is warranted to evaluate its long-term effectiveness and potential health implications.