Continuous versus Intermittent Dieting for Fat Loss and Fat-Free Mass Retention in Resistance-trained Adults: The ICECAP Trial

Introduction Can intermittent energy restriction (IER) improve fat loss and fat-free mass retention compared with continuous energy restriction (CER) in resistance-trained adults? Methods Sixty-one adults (32 women) with a mean (SD) age of 28.7 (6.5) yr, body weight of 77.2 (16.1) kg, and body fat of 25.5% (6.1%) were randomized to 12 wk of 1) 4 × 3 wk of moderate (m) energy restriction interspersed with 3 × 1 wk of energy balance (mIER; n = 30; 15 wk total) or 2) 12 wk of continuous moderate energy restriction (mCER; n = 31). Analyses of all outcome measures were by intention-to-treat. Results After accounting for baseline differences, mIER did not result in lower fat mass or body weight, or greater fat-free mass, compared with mCER after energy restriction. Mean (and 97.5% confidence interval for fat mass at the end of mIER versus mCER was 15.3 (12.5-18.0) kg versus 18.0 (14.3-21.7) kg (P = 0.321), that for fat-free mass was 56.7 (51.5-61.9) kg versus 56.7 (51.4-62.0) kg (P = 0.309), and that for body weight (with 95% confidence interval) was 72.1 (66.4-77.9) versus 74.6 (69.3-80.0) (P = 0.283). There were no differences between interventions in muscle strength or endurance or in resting energy expenditure, leptin, testosterone, insulin-like growth factor-1, free 3,3',5-triiodothyronine or active ghrelin, or in sleep, muscle dysmorphia, or eating disorder behaviors. However, participants in mIER exhibited lower hunger (P = 0.002) and desire to eat (P = 0.014) compared with those in mCER, and greater satisfaction (P = 0.016) and peptide YY (P = 0.034). Conclusions Similar fat loss and fat-free mass retention are achieved with mIER and mCER during 12 wk of energy restriction; however, mIER is associated with reduced appetite.