No changes in time trial performance of master endurance athletes after 4 weeks on a low carbohydrate diet

The purpose of the present study was to evaluate the effects of a 4-week low-carbohydrate (CHO) diet regimen on body weight, exercise performance and hormonal response to running in master athletes. Six endurance master athletes performed three 30-min time trials, before (TT1), after 15 days (TT2) and after 30 days (TT3) on a low CHO diet. Blood samples were collected for hormonal and lactate measurements. After 15 days body weight had decreased (TT1 72.3 ± 2.4 kg, TT2 70.0 ± 2.7 kg; P = 0.006) and then remained stable. No differences were observed in performance (TT1 7,015 ± 273 m, TT2 6,920 ± 286 m, TT3 7,202 ± 315 m) and in the insulin/glucagon ratio. After 2 and 4 weeks, adrenocorticotropic hormone decreased significantly both at rest (baseline: TT1 42.5 ± 7.8 pg·ml −1 , TT3 21.6 ± 3.2 pg·ml −1 ) and during exercise (end of exercise: TT1 120 ± 20 pg·ml −1 , TT2 80 ± 16 pg·ml −1 , TT3 31 ± 2 pg·ml −1 ). Baseline cortisol concentrations had increased significantly after as little as 15 days on the low CHO diet. The results of the present study demonstrate no changes in time trial performance in master endurance athletes after 4 weeks on a low CHO diet. However, an effect on the hypothalamic pituitary adrenal axis emerged.