Hormonal changes in normal men under marginally negative energy balance

Abstract

Six men were confined to a metabolic unit for 105 days. Their assigned work and energy intake were varied throughout six metabolic periods in order to create either a marginally negative (−15%) or an equilibrated energy balance. They were fed a defined diet providing a constant amount of protein. At each metabolic period, T₄, T₃, reverse T₃(_rT₃), free T₃, free reverse T₃, thyroid-stimulating hormone, cortisol, cortisol-binding globulin, testosterone, and testosterone/estradiol-binding globulin were measured. Free urinary cortisol was measured daily. Results show that serum thyroid hormones are sensitive to marginal changes in energy intake, expenditure, and balance. The ratio T₄/T₃ appears to be more sensitive to the balance itself, with the ratio T₃/_rT₃ being more sensitive to the intake and expenditure level at which this balance is established. Regulations of T₃ and _rT₃ production are probably distinct. Urinary cortisol did not show any variation that could be related to the energy balance. However, daily urinary cortisol was correlated to daily urinary nitrogen excretion. No change in serum testosterone was found.