Resting And Endurance Exercise-induced Testosterone Responses In Elite Ultra-runners Habitually Consuming Low-carbohydrate And High-carbohydrate Diets: 311 Board #162 May 27, 11

Low testosterone (T) is associated with reduced muscle mass and bone mineral density. Ultra-marathoners are more susceptible to training-induced hypogonadism (TIH) but it is unknown if diet manipulation can mitigate this phenomenon. A growing number of elite ultra-endurance athletes have adopted a high-fat, moderate-protein, low-carbohydrate diet to enhance performance and speed recovery. Previous studies indicate that diets higher in fat are associated with increased T but it is not known if ultra-marathoners respond similarly. PURPOSE: To examine resting and exercise-induced T in high-level ultra-endurance athletes consuming either low-carbohydrate/high-fat (LCD) or high-carbohydrate/low-fat diets (HCD). METHODS: 20 elite level ultra-running men (age 33.5 ± 6.4 yr, BMI 22.6 ± 3.3 kg/m2, VO2max 64.5 ± 4.9 mL/kg/min) habitually consuming a HCD (n=10; 58% CHO, 15% PRO, 28% FAT) or a LCD (n=10; 11% CHO, 19% PRO, 71% FAT) were matched for age and performance. They performed a 3 hr run at 65% VO2max. A shake (5 kcal/kg lean body mass) similar in macronutrient composition to the habitual diet was consumed 90 min pre-exercise and immediately post exercise (IP). Serial blood samples were taken after an overnight fast at baseline (BL), during the run (Run60 and Run120 minutes), IP, and during recovery (+30, +60, and +120 minutes). Serum levels of total T were analyzed enzymatically. RESULTS: There were no significant differences in T between groups. Fasting T concentrations were below normal (<14 nmol/L) in 85% of participants. Mean T (95% CI) was 11.3 (7.4 – 15.2 nmol/L) in the HCD and 10.2 (7.0 – 13.4 nmol/L) in the LCD athletes. Compared to BL, T gradually increased during exercise, peaked at IP (HCD 86%; LCD 47%) (P<0.05), and progressively decreased after exercise falling below BL at +120 (HCD 7.7±1.3 nmol/L; LCD 8.1±1.1 nmol/L). CONCLUSION: This group of high-level ultra-endurance runners had a high prevalence of low circulating T; they showed a modest transient rise IP followed by a decline below BL post-exercise irrespective of habitual diet composition. Lower resting T and its descending response after exercise may be due to a greater turnover of the androgen receptor pulling T out of circulation. This may be due to the shake pre/post run or a reduced LH pulse reflected in altered hypothalamic-pituitary cybernetic changes.