Sustained Exposure to High Carbohydrate Availability Does Not Influence Iron-Regulatory Responses in Elite Endurance Athletes

Abstract

This study implemented a 2-week high carbohydrate (CHO) diet intended to maximize CHO oxidation rates and examined the iron-regulatory response to a 26-km race walking effort. Twenty international-level, male race walkers were assigned to either a novel high CHO diet (MAX = 10 g/kg body mass CHO daily) inclusive of gut-training strategies, or a moderate CHO control diet (CON = 6 g/kg body mass CHO daily) for a 2-week training period. The athletes completed a 26-km race walking test protocol before and after the dietary intervention. Venous blood samples were collected pre-, post-, and 3 hr postexercise and measured for serum ferritin, interleukin-6, and hepcidin-25 concentrations. Similar decreases in serum ferritin (17–23%) occurred postintervention in MAX and CON. At the baseline, CON had a greater postexercise increase in interleukin-6 levels after 26 km of walking (20.1-fold, 95% CI [9.2, 35.7]) compared with MAX (10.2-fold, 95% CI [3.7, 18.7]). A similar finding was evident for hepcidin levels 3 hr postexercise (CON = 10.8-fold, 95% CI [4.8, 21.2]; MAX = 8.8-fold, 95% CI [3.9, 16.4]). Postintervention, there were no substantial differences in the interleukin-6 response (CON = 13.6-fold, 95% CI [9.2, 20.5]; MAX = 11.2-fold, 95% CI [6.5, 21.3]) or hepcidin levels (CON = 7.1-fold, 95% CI [2.1, 15.4]; MAX = 6.3-fold, 95% CI [1.8, 14.6]) between the dietary groups. Higher resting serum ferritin (p = .004) and hotter trial ambient temperatures (p = .014) were associated with greater hepcidin levels 3 hr postexercise. Very high CHO diets employed by endurance athletes to increase CHO oxidation have little impact on iron regulation in elite athletes. It appears that variations in serum ferritin concentration and ambient temperature, rather than dietary CHO, are associated with increased hepcidin concentrations 3 hr postexercise.

Six Days of Low Carbohydrate, Not Energy Availability, Alters the Iron and Immune Response to Exercise in Elite Athletes

“…Models included fixed effects for dietary group and testing phase (resting variables) or dietary group, testing phase and time point (postexercise responses), with random intercepts for subject identification, camp and environmental temperature included to adjust for Baseline levels and interindividual homogeneity. Given the strong influence that iron status can have on the postexercise hepcidin response (17), serum ferritin was used as a covariate in the analysis of hepcidin, as undertaken previously (18). Statistical significance of the fixed effects were determined using type II Wald tests with Kenward-Roger degrees of freedom.…”

Physiological responses to carbohydrate overfeeding

“…The mechanisms through which exercise can benefit metabolic health in the face of carbohydrate overfeeding may therefore involve a direct influence of muscle contraction and/or the regular depletion and replenishment of muscle and liver glycogen. One particular signal from skeletal muscle in response to carbohydrate-depleting exercise is the pleiotropic cytokine Interleukin-6 (IL-6), which is involved in both glucose and iron metabolism following exercise, although sustained high carbohydrate availability does not appear to modify these exercise-induced responses [34]. However, sustained overfeeding can alter the expression of genes involved in regulating carbohydrate, lipid and iron homeostasis in skeletal muscle and adipose tissue [32,35,36].…”