Negative energy balance in male and female rangers: effects of 7 d of sustained exercise and food deprivation1–4

Background: 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. Objective: We quantified total energy expenditure (TEE), food intake, and changes in body composition in male and female cadets. Design: TEE (measured by doubly labeled water), food intake, activity patterns (measured by accelerometry), and body composi-tion (measured by dual-energy X-ray absorptiometry) were mea-sured in 16 cadets (10 men and 6 women aged 21–27 y). Results: The physically active (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, 34326 kJ · kg1 · d1; women, 354 18 kJ · kg1 · d1; 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 · min1 · kg FFM1; women, 7.3 0.5 mg · min1 · kg FFM1) and the relative contri-bution of FM to TEE (men, 74 14%; women, 89 6%) were significantly greater in women than in men (P 0.05). Conclusion: Female cadets maintained a significantly more fat-predominant fuel metabolism than did male cadets in response to sustained exercise and semistarvation. Am J Clin Nutr 2006;83