Responsiveness of the reproductive axis to a single missed evening meal in young adult males

Objectives: The male reproductive axis is responsive to energetic deficits, including multiday fasts, but little is known about brief periods of fasting (<24 hours). Reduced testosterone in low-energy balance situations is hypothesized to reflect redirection of resources from reproduction to survival. This study tests the hypothesis that testosterone levels decrease during a minor caloric deficiency by assessing the effects of a single missed (evening) meal on morning testosterone in 23 healthy male participants, age 19-36. Methods: Participants provided daily saliva and urine samples for two baseline days and the morning following an evening fast (water only after 4 PM). Testosterone, cortisol, and luteinizing hormone were measured with enzyme immunoassays. Results: Fasting specimens had significantly lower overnight urinary luteinizing hormone (P = 0.045) and morning salivary testosterone than baseline (P = 0.037). In contrast to morning salivary testosterone, there was a significant increase in overnight urinary testosterone (P = 0.000) following the evening fast, suggesting an increase in urinary clearance rates. There was a marginal increase in overnight urinary cortisol (P = 0.100), but not morning salivary cortisol (P = 0.589). Conclusion: These results suggest the male reproductive axis may react more quickly to energetic imbalances than has been previously appreciated.