Purpose To quantify the effects of a short-term (6-d) low carbohydrate (CHO) high fat (LCHF), and low energy availability (LEA) diet on immune, inflammatory, and iron-regulatory responses to exercise in endurance athletes. Methods Twenty-eight elite male race walkers completed two 6-d diet/training phases. During phase 1 (Baseline), all athletes consumed a high CHO/energy availability (CON) diet (65% CHO and ~40 kcal·kg-1 fat-free mass (FFM)·d-1). In phase 2 (Adaptation), athletes were allocated to either a CON (n = 10), LCHF (n = 8; <50 g·d-1 CHO and ~40 kcal·kg-1·FFM-1·d-1), or LEA diet (n = 10; 60% CHO and 15 kcal·kg-1·FFM-1·d-1). At the end of each phase, athletes completed a 25-km race walk protocol at ~75% V?O2max. On each occasion, venous blood was collected before and after exercise for interleukin-6, hepcidin, cortisol, and glucose concentrations, as well as white blood cell counts. Results The LCHF athletes displayed a greater IL-6 (P = 0.019) and hepcidin (P = 0.011) response to exercise after Adaptation, compared with Baseline. Similarly, postexercise increases in total white blood cell counts (P = 0.026) and cortisol levels (P < 0.001) were larger compared with Baseline after LCHF Adaptation. Decreases in blood glucose concentrations were evident postexercise during Adaptation in LCHF (P = 0.049), whereas no change occurred in CON or LEA (P > 0.05). No differences between CON and LEA were evident for any of the measured biological markers (all P > 0.05). Conclusions Short-term adherence to a LCHF diet elicited small yet unfavorable iron, immune, and stress responses to exercise. In contrast, no substantial alterations to athlete health were observed when athletes restricted energy availability compared with athletes with adequate energy availability. Therefore, short-term restriction of CHO, rather than energy, may have greater negative impacts on athlete health.
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