The Effects of Continuous vs. Intermittent Caloric Restriction on Fat Loss: A Randomized Controlled Trial

Background/Objectives: Obesity remains difficult to treat effectively, not because weight loss cannot be achieved, but because it is difficult to sustain in the face of physiological adaptations to energy restriction, including reductions in resting metabolic rate and loss of fat-free mass. Dietary strategies that preserve favorable body composition while supporting long-term adherence are therefore needed. The purpose of this study was to compare continuous caloric restriction (CCR) with an intermittent approach incorporating structured diet refeeds and planned diet breaks (DRF) on body composition outcomes in adult women with obesity. Methods: Thirty adult females (18-65 years; BMI 30-45 kg·m^-2) were randomized to 12 weeks of CCR or DRF following a two-week maintenance phase used to determine individualized caloric needs. Both groups were prescribed a 25% caloric deficit and protein intake of 1.2 g·kg^-1·day^-1. Body composition, including body fat percentage, fat mass, and fat-free mass, was assessed using air-displacement plethysmography at baseline and post-intervention. Results: Repeated-measures ANOVA revealed a significant main effect of time for body fat percentage (p < 0.001), which decreased by 6.7 ± 2.1% in the CCR group and 6.0 ± 1.9% in the DRF group, with no significant group × time interaction (p > 0.05). Fat mass significantly declined in both groups (p < 0.001), with reductions of 9.30 ± 2.77 kg (CCR) and 9.21 ± 2.63 kg (DRF); between-group differences were negligible (p > 0.05; Cohen's d = 0.03). Fat-free mass increased over time (p < 0.05); although the interaction was not significant (p = 0.08), the DRF group demonstrated a moderate effect size advantage. Despite similar changes in body composition, analysis of energy balance revealed a significantly greater daily energy deficit in the CCR group compared with DRF (-1005 ± 515 vs. -690 ± 120 kcal·day^-1, p = 0.041), indicating a higher achieved level of caloric restriction in CCR. Conclusions: Both dietary strategies effectively reduced fat mass in females with obesity; however, incorporating diet breaks was associated with a nonsignificant trend toward greater preservation or accrual of fat-free mass without compromising fat loss. Future studies should investigate this potential association in larger, adequately powered trials before any conclusions regarding metabolic adaptation or practical advantage can be drawn.