Sex differences in energy balance, body composition, and metabolic and endocrine markers during prolonged arduous military training.

This study investigated sex differences in energy balance, body composition, and metabolic and endocrine markers during prolonged military training. Twenty-three trainees (14 women) completed 44-weeks military training (three terms of 14 weeks with 2 weeks adventurous training). Dietary intake and total energy expenditure were measured over 10 days during each term by weighed food and doubly labelled water. Body composition was measured by DXA at baseline and the end of each term. Circulating metabolic and endocrine markers were measure at baseline and the end of terms 2 and 3. Absolute energy intake and total energy expenditure were higher, and energy balance was lower, for men than women (p ≤ 0.008). Absolute energy intake and balance were lower, and total energy expenditure was higher, during term 2 than terms 1 and 3 (p < 0.001). Lean mass did not change with training (p = 0.081). Fat mass and body fat increased from term 1 to terms 2 and 3 (p ≤ 0.045). Leptin increased from baseline to terms 2 and 3 in women (p ≤ 0.002) but not men (p ≥ 0.251). Testosterone and free androgen index increased from baseline to term 3 (p ≤ 0.018). Free T4 decreased and TSH increased from baseline to term 2 and term 3 (p ≤ 0.031). Cortisol decreased from baseline to term 3 (p = 0.030). IGF-I and total T3 did not change with training (p ≥ 0.148). Men experienced greater energy deficits than women during military training due to higher total energy expenditure.