Strategic carbohydrate feeding improves performance in ketogenic trained athletes

Area of Science:

• Sports Science
• Human Physiology
• Nutritional Biochemistry

Background:

• Ketogenic diets (KDs) induce metabolic shifts impacting exercise performance and carbohydrate metabolism.
• Research on KD efficacy for endurance is inconsistent, with some studies showing no performance impairment in sub-elite athletes.
• The effects of carbohydrate reintroduction timing on performance in chronically ketogenic athletes remain unexplored.

Purpose of the Study:

• To investigate the impact of varying carbohydrate (CHO) feeding timings and dosages on exercise performance and physiological responses.
• To examine the effects of pre-exercise CHO intake in athletes with long-term ketogenic diet adherence (≥12 months).

Main Methods:

• Recreational athletes (n=13) with ≥12 months of KD adherence participated in a single-blinded crossover study.
• Four experimental conditions tested different timings and dosages of CHO or placebo ingestion over two days prior to and immediately before exercise.
• Performance was assessed via a 16.1 km time trial, with V˙O2max determined separately.

Main Results:

• A pre-exercise carbohydrate bolus significantly improved 16.1 km time trial performance compared to placebo.
• Carbohydrate consumption in the 48 hours preceding exercise did not significantly affect performance.
• No significant differences were observed in performance between CHO consumed 48 hours prior and placebo.

Conclusions:

• Carbohydrate ingestion enhances exercise performance primarily when consumed immediately before exercise in ketogenic athletes.
• The ergogenic effects are likely mediated by central nervous system mechanisms or prevention of hypoglycemia, not delayed metabolic pathways.
• Distinct roles of muscle and liver glycogen in performance warrant further investigation.