Hungry runners – low energy availability in male endurance athletes and its impact on performance and testosterone

Summary

Narrative review consolidating the evidence base for relative energy deficiency in male athletes — the male-specific extension of the original female RED-S framework. The authors synthesize controlled trials and observational cohorts showing that male endurance athletes operating below approximately 30 kcal/kg fat-free mass per day for as little as five days exhibit measurable HPG-axis disruption: LH pulsatility falls, total testosterone falls, T3 falls, and bone-formation markers fall. In elite male endurance runner cohorts, total testosterone runs 55–85% of age-matched sedentary norms, roughly 40% of one cohort showed clinically low testosterone, and bone stress injury risk runs approximately 4.5× control. The paper extends the Loucks 2003 30 kcal/kg/day energy availability threshold from women to lean male athletes.