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

Abstract

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-wk military training (three terms of 14 wk with 2-wk adventurous training). Dietary intake and total energy expenditure were measured over 10 days during each term by weighed food and doubly labeled water. Body composition was measured by dual-energy X-ray absorptiometry (DXA) at baseline and at the end of each term. Circulating metabolic and endocrine markers were measured at baseline and at 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 in men (P ≥ 0.251). Testosterone and free androgen index increased from baseline to term 3 (P ≤ 0.018). Free thyroxine (T4) decreased and thyroid-stimulating hormone (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 triiodothyronine (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.NEW & NOTEWORTHY Energy deficits are common in military training and can result in endocrine and metabolic disturbances. This study provides first investigation of sex differences in energy balance, body composition, and endocrine and metabolic markers in response to prolonged and arduous military training. Men experienced greater energy deficits than women due to higher energy expenditure, which was not compensated for by increased energy intake. These energy deficits were not associated with decreases in fat or lean mass or metabolic or endocrine function.

Keywords: body composition; musculoskeletal injury; nutrition; performance.

Graphical abstract

Figure 1.

Absolute and relative energy intake, total energy expenditure, and energy balance for men and women during training. Data are presented as means ± SD. Open circles are individual data. ^aP < 0.05 main effect of sex; ^bP < 0.05 vs. men at same time point, ^cP < 0.05 vs. term 1 (men and women pooled); ^dP < 0.05 vs. term 3 (men and women pooled); ^eP < 0.05 vs. term 1 (post hoc); ^fP < 0.05 vs. term 3 (post hoc).

Figure 2.

Absolute and relative carbohydrate, protein, and fat intake for men and women during training. Data are presented as means ± SD. Open circles are individual data. ^aP < 0.05 main effect of sex; ^bP < 0.05 vs. men at same time point (post hoc), ^cP < 0.05 vs. term 1 (men and women pooled); ^dP < 0.05 vs. term 3 (men and women pooled); ^eP < 0.05 vs. term 1 (post hoc); ^fP < 0.05 vs. term 3 (post hoc).

Figure 3.

Lean mass, fat mass, and body fat for men and women during training. Data are presented as means ± SD. Open circles are individual data. ^aP < 0.05 vs. men (main effect of sex); ^bP < 0.05 vs. term 1 (men and women pooled); ^cP < 0.05 vs. baseline (men and women pooled); ^dP < 0.05 vs. baseline (post hoc); ^eP < 0.05 vs. term 1 (post hoc).

Figure 4.

Markers of metabolic and endocrine function during training. Data are presented as means ± SD. Open circles are individual data. ^aP < 0.05 vs. men (main effect of sex); ^bP < 0.05 vs. men at same time point (post hoc); ^cP < 0.05 vs. baseline (men and women pooled); ^dP < 0.05 vs. term 2 (men and women pooled); ^eP < 0.05 vs. baseline (post hoc); ^fP < 0.05 vs. term 2 (post hoc).

Figure 5.

Markers of bone metabolism during training. Data are presented as means ± SD overlaid with individual data.