Endocrine markers of semistarvation in healthy lean men in a multistressorenvironment

We tested the hypothesis that key endocrine responses to semistarvation wou ld be attenuated by changing only the food intake in a multistressor enviro nment that also included sustained workload, inadequate sleep, and thermal strain. Serum hormones were compared within and between two groups of healt hy young male volunteers participating in the 8-wk US Army Ranger course, w ith four repeated cycles of restricted energy intakes and refeeding: group I (n = 49) and group 2 (n = 48); energy deficits averaged 1,200 and 1,000 k cal/day, respectively. After 8 wk, most of group I achieved a minimum body fat, serum 3,5,3'-triiodothyronine (T-3) was below normal (78 +/- 20 ng/dl) , testosterone (T) approached castrate levels (4.5 +/- 3.9 nmol/l), insulin -like growth factor I(IGF-I) declined by one-half(75 +/- 25 mu g/l), and ch olesterol rose from 158 +/- 31 to 217 +/- 39 mg/dl. Bioavailable T3 and T w ere further reduced by increases in their specific binding proteins in resp onse to declining insulin. Refeeding, even with continuation of the other s tressors, produced prompt recovery of Ts, T, and IGF-I. Higher energy intak es ingroup 2 attenuated the subclinical hypothyroidism and hypercholesterol emia, whereas consistent luteinizing hormone suppression indicated centrall y mediated threshold effects on gonadal hormone suppression. We conclude th at low T, TS, and IGF-I remained reliable markers of acute energy deficits in the presence of other stressors; elevated cholesterol and cortisol provi ded information about chronic status, corresponding to diminishing body fat stores.