Increased carbohydrate availability partially attenuates endocrine suppression in response to low-energy availability

Low-energy availability (LEA) results in characteristic endocrine and metabolic adaptations, yet the contribution of carbohydrate availability (CA), defined as the difference between carbohydrate intake and oxidation during exercise, remains unclear. This randomized crossover study examined whether CA modulates endocrine and metabolic responses to LEA. Sixteen recreationally active adults (female, n = 9) completed two 4-day conditions of LEA [25 kcal·kg fat-free mass (FFM)^-1·day^-1] with low and high CA (1.5 vs. 4.0 g·kg^-1·day^-1). Diets were fully controlled, and participants performed daily exercise expending 20 kcal·kg FFM^-1·day^-1. Independent of conditions, LEA led to reductions in body mass (mean relative change: -1.3%; P < 0.001). High CA significantly attenuated the LEA-induced decline in insulin-like growth factor 1 (IGF-1; -22.9 ± 29.6 vs. -48.5 ± 26.2 ng·mL^-1; P = 0.018). Insulin, leptin, and testosterone also exhibited greater decreases in low vs. high CA, although condition × time interactions did not achieve significance. LEA induced a shift toward greater fat oxidation at rest and during exercise, which was not modulated by CA but by sex. High CA mitigated reductions in submaximal and maximal blood lactate concentrations, indicating partial preservation of glycolytic function. Maximal performance indices (i.e., peak oxygen uptake and maximal power output) were neither affected by LEA nor by condition. These findings demonstrate that increasing CA under conditions of short-term LEA partially offsets endocrine responses, particularly the reduction in IGF-1, and attenuates reductions in blood lactate concentrations. Shifts in substrate utilization in response to LEA are largely independent of CA.NEW & NOTEWORTHY Low-energy availability (LEA) is often confounded by low carbohydrate availability. In a randomized crossover trial, we demonstrate that maintaining high carbohydrate availability (CA) during short-term LEA attenuates reductions in insulin-like growth factor 1 (IGF-1). In addition, we show that the modulatory effect of CA on changes in substrate utilization differs between sexes.