Endocrine markers of semistarvation in healthy lean men in a multistressor environment

Abstract

We tested the hypothesis that key endocrine responses to semistarvation would be attenuated by changing only the food intake in a multistressor environment that also included sustained workload, inadequate sleep, and thermal strain. Serum hormones were compared within and between two groups of healthy young male volunteers participating in the 8-wk US Army Ranger course, with four repeated cycles of restricted energy intakes and refeeding: group 1 (n = 49) and group 2 (n = 48); energy deficits averaged 1,200 and 1,000 kcal/day, respectively. After 8 wk, most of group 1 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 microg/l), and cholesterol rose from 158 +/- 31 to 217 +/- 39 mg/dl. Bioavailable T(3) and T were further reduced by increases in their specific binding proteins in response to declining insulin. Refeeding, even with continuation of the other stressors, produced prompt recovery of T(3), T, and IGF-I. Higher energy intakes in group 2 attenuated the subclinical hypothyroidism and hypercholesterolemia, whereas consistent luteinizing hormone suppression indicated centrally mediated threshold effects on gonadal hormone suppression. We conclude that low T, T(3), and IGF-I remained reliable markers of acute energy deficits in the presence of other stressors; elevated cholesterol and cortisol provided information about chronic status, corresponding to diminishing body fat stores.

How dieting makes some fatter: from a perspective of human body composition autoregulation

“…In more recent years, similar body weight and fat overshooting have also been reported in young men at the US Army Ranger School recovering from about 12% of weight lost following 8-9 weeks of training in a multistressor environment that includes energy deficit and sleep deprivation (36)(37)(38) . Nindl et al (36) found that at week 5 in the post-training recovery phase, body weight had overshot by 5 kg, reflected primarily in large gains in fat mass, with all ten subjects showing higher fat mass than before weight lost.…”

Utility of Measuring Insulin-Like Growth Factor-I for Assessing Military Operational Stress: Supporting Future Force Warrior from the Bench Top to the Battlefield

“…The physiological strain produced by these operational stressors can have deleterious effects on muscle mass, endocrine and metabolic function, as well as physical and mental performance (Friedl et al, 1994;Friedl, 1999;Friedl et al, 2000;Nindl et al, 1997;Nindl et al, 2002;Nindl et al, 2003a;Nindl et al, 2003b) (see Figure 1). A goal of the Army Medical Research and Materiel Command's (MRMC) biomedical research program is to identify useful biomarkers that are indicative of nutritional and physiological status that can be assessed rapidly, with minimally or non-invasive collection methods.…”

“…The growth hormone/insulin-like axis is a central endocrine axis and is thought to mediate many of the somatotrophic changes that are observed when warfighters are exposed to harsh field environments (Florini et al, 1996;Friedl et al, 2000;Nindl et al 2003a;Rosen, 1999;Rosendal et al, 2002). For this reason, periodic assessment of the growth hormone/insulin-like growth factor axis may have utility for sustaining warfighter health and performance.…”

“…The appeal of IGF-I as a biomarker is the dynamic nature in which circulating concentrations respond to nutritional stress. Underfeeding and proteincalorie malnutrition result in substantial reductions in IGF-I concentrations and the response persists until the nutritional stress is removed (Friedl et al, 2000;Frystyk et al, 1999;Nindl et al, 2003a;Rand et al, 2003;Thissen et al, 1992;Thissen et al, 1999). Additionally, IGF-I concentrations are relatively stable.…”

“…Friedl and colleagues performed experimental studies characterizing the physiological responses of soldiers participating in the U.S. Army Ranger Training Course (Friedl et al, 1994;Friedl et al, 2000;Nindl et al, 1997). The data provide insight into the adaptive process that occurs as soldiers cope with sustained physical work, energy restriction and sleep disruption.…”