Less-than-expected weight loss in normal-weight women undergoing caloric restriction and exercise is accompanied by preservation of fat-free mass and metabolic adaptations

Background/Objectives: Normal-weight women frequently restrict their caloric intake and exercise, but little is known about the effects on body weight, body composition and metabolic adaptations in this population. Subjects/Methods: We conducted a secondary analysis of data from a randomized controlled trial in sedentary normal-weight women. Women were assigned to a severe energy deficit (SEV: –1062 ± 80 kcal per day; n = 9), a moderate energy deficit (MOD: –633 ± 71 kcal per day; n = 7) or energy balance (BAL; n = 9) while exercising five times per week for 3 months. Outcome variables included changes in body weight, body composition, resting metabolic rate (RMR) and metabolic hormones associated with energy conservation. Results: Weight loss occurred in SEV (–3.7 ± 0.9 kg, P\u3c0.001) and MOD (–2.7 ± 0.8 kg; P = 0.003), but weight loss was significantly less than predicted (SEV: –11.1 ± 1.0 kg; MOD: –6.5 ± 1.1 kg; both P\u3c0.001 vs actual). Fat mass declined in SEV (P\u3c0.001) and MOD (P = 0.006), whereas fat-free mass remained unchanged in all groups (P40.33). RMR decreased by − 6 ± 2% in MOD (P = 0.020). In SEV, RMR did not change on a group level (P = 0.66), but participants whose RMR declined lost more weight (P = 0.020) and had a higher baseline RMR (P = 0.026) than those whose RMR did not decrease. Characteristic changes in leptin (P = 0.003), tri-iodothyronine (P = 0.013), insulin-like growth factor-1 (P = 0.016) and ghrelin (P = 0.049) occurred only in SEV. The energy deficit and adaptive changes in RMR explained 54% of the observed weight loss. Conclusions: In normal-weight women, caloric restriction and exercise resulted in less-than-predicted weight loss. In contrast to previous literature, weight loss consisted almost exclusively of fat mass, whereas fat-free mass was preserved