¹Department of Anthropology, University of California Santa Barbara, ²Department of Anthropology, University of New Mexico, ³Department of Anthropology, Hunter College, City University of New York

March 26, 2015 11:30, Grand Ballroom D

Testosterone is thought to mediate energetic allocation between reproduction and survival. Energetic deficits from caloric restriction or high pathogen burden lead to rapid down regulation of testosterone production. The anabolic effects of testosterone are well established, increasing lean muscle mass, which results in greater energetic expenditure, though it is unclear if circulating testosterone increases energetic expenditure beyond the role it has in lean muscle mass. Here we examine whether testosterone is associated with higher total daily energy expenditure (TEE kCal/day) as measured by doubly labeled water (DLW) in forty Tsimane forager-horticulturalists practicing a traditional subsistence lifestyle of hunting, foraging and horticulture. Twenty men aged 20-77 (median 47.5) years, and 20 females aged 18-87 (median 48.5) years drank DLW (120 g; 10% H₂¹⁸O, 6% ²H₂O) and provided urine specimens over a nine day period. Average TEE (kCal/day) was calculated from ¹⁸O and ²H isotope depletion, and testosterone was measured via enzyme immunoassay in first morning urine samples. Controlling for age, sex, and lean muscle mass, testosterone was positively associated with TEE (Std. β = 0.28, p=0.030). Males showed a stronger association between testosterone and TEE (Std. β = 0.45, p=0.018) than women (Std. β = 0.01, p=0.979), controlling for age and lean muscle mass. These results indicate that energetic costs of a high testosterone phenotype exceed the costs of muscle mass alone, even in lean forager-horticulturalists with relatively low levels of testosterone. Testosterone is an important mediator of many aspects of male physiology beyond muscle mass, including potentially energetically expensive behaviors.

Grant Sponsorship: NIA R01AG024119-01, R56AG024119-06, R01AG024119-07