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<0.001) 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<0.001 vs actual). Fat mass declined in SEV (P<0.001) and MOD (P=0.006), whereas fat-free mass remained unchanged in all groups (P>0.33). 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.