LOWER LIMIT OF BODY-FAT IN HEALTHY ACTIVE MEN

We examined body composition changes in 55 normal young men during an 8-wk Army combat leadership training course involving strenuous exerci se and low energy intake, with an estimated energy deficit of 5.0 +/- 2.0 MJ/day and a resultant 15.7 +/- 3.1% weight loss. Percent body fat (BF) measured by dual-energy X-ray absorptiometry (DEXA) averaged 14. 3% (range 6-26%) and 5.8 +/- 1.8% (range 4-11%) at the beginning and e nd of the course, respectively. Men who achieved a minimum percent BF (4-6%) by 6 wk demonstrated only small additional total and subcutaneo us fat losses in the final 2 wk and sacrificed increasingly larger pro portions of fat-free mass. Percent BF estimated from skinfold thicknes ses reflected relative changes in fat mass, although actual percent BF was overestimated. Instead of reaching a plateau after fat stores wer e substantially depleted, abdominal, hip, and thigh girths continued t o decline with body weight loss. Final percent BF for the leanest men was similar to that observed after a 25% body weight reduction in the 1950 Minnesota study (5.2% by underwater weighing), and height-correct ed final fat mass was the same (1.0 +/- 0.2 vs. 0.9 +/- 0.7 kg fat/m(2 )), suggesting that these values represent a minimal body fat content in healthy men and that weight loss subsequent to achieving this level is contributed from the fat-free mass. Our results suggest that 4-6% BF or similar to 2.5 kg fat represents the lower limit for healthy men , as assessed by DEXA or by underwater weighing.