Low-Carb Erodes Endurance Performance Gains, Even with Caffeine

Caffeine improves performance across diets — but high carbohydrate availability still wins at race pace.

You don’t see many low-carb or keto athletes dominating the ranks of high-level endurance sports (really, any sport for that matter). And there’s a good reason for this — carbs are king when it comes to exercise performance. When you cut them out, adaptation suffers, and one’s performance ceiling drops…at least that’s what the research shows.

Leading the way in this field is a team headed by Dr. Louise Burke, who, over the last decade of running tightly controlled human studies, has tested versions of “fat adaptation” and ketogenic (low-carb, high-fat or LCHF) strategies in trained and elite endurance athletes.

A consistent pattern is clear — low-carb approaches reliably increase fat oxidation, but at the speeds that decide races (when it really matters), they also increase the oxygen cost of movement (worsen economy) and blunt the normal performance gains from hard training. High-carb strategies, including periodized carbohydrate availability, enable faster training and better race outcomes. Surprisingly, even brief LCHF “blocks” don’t create a later performance rebound once carbs are reintroduced.