Negative energy balance in male and female rangers: effects of 7 d of sustained exercise and food deprivation

Abstract

A challenging 7-d ranger field exercise (FEX) by cadets in the Norwegian Military Academy provided a venue in which to study the effects of negative energy balance. We quantified total energy expenditure (TEE), food intake, and changes in body composition in male and female cadets. TEE (measured by doubly labeled water), food intake, activity patterns (measured by accelerometry), and body composition (measured by dual-energy X-ray absorptiometry) were measured in 16 cadets (10 men and 6 women aged 21-27 y). The physically active (approximately 23 h/d) and semistarved (0.2-2.2 MJ/d) cadets lost weight (x +/- SD: men, -7.7 +/- 1.1 kg; women, -5.9 +/- 1.1 kg; P < 0.05). Absolute TEE differed by sex (men, 26.6 +/- 2.0 MJ/d; women, 21.9 +/- 2.0 MJ/d; P < 0.05) but body weight-specific TEE did not (men, 343 +/- 26 kJ . kg(-1) . d(-1); women, 354 +/- 18 kJ . kg(-1) . d(-1); NS). Fat-free mass (FFM) loss differed significantly by sex (men, -4.0 +/- 1.2 kg; women, -2.5 +/- 1.1 kg; P < 0.05), but percentage FFM loss did not (men, -6.3 +/- 1.9%; women, -5.6 +/- 2.4%). In contrast, absolute FM loss did not differ significantly by sex (men, -3.45 +/- 0.72 kg; women, -3.42 +/- 0.22 kg), but fat oxidation (men, 5.2 +/- 1.0 mg . min(-1) . kg FFM(-1); women, 7.3 +/- 0.5 mg . min(-1) . kg FFM(-1)) and the relative contribution of FM to TEE (men, 74 +/- 14%; women, 89 +/- 6%) were significantly greater in women than in men (P < 0.05). Female cadets maintained a significantly more fat-predominant fuel metabolism than did male cadets in response to sustained exercise and semistarvation.