RUN LONG, RUN HEALTHY — SEPTEMBER 25, 2025

Does Carb Loading Actually Work?

Plus, vitamin D and NSAIDs for ultra-running; hacking heat acclimation; hot water immersion as a recovery tool; and the mental health challenges of “multi-marathoning”

Does Carb Loading Work?

Few topics in endurance sports spark as much debate as carbohydrate loading. Ever since landmark studies in the 1960s showed that exhaustive exercise followed by a few days of high-carb eating could double muscle glycogen, athletes have treated “carb loading” like gospel before marathons. But the science has been a bit patchy: Some studies confirm massive glycogen boosts while others show little change, and the differences between running and cycling protocols have muddied the waters.

A new systematic review and meta-analysis of 30 studies and 319 participants pulls together decades of research to finally answer the question: How much glycogen supercompensation really happens, and what factors influence it?

To be included, each study had to involve an exercise session that depleted glycogen, a subsequent 3–5 day high-carbohydrate diet, and direct measurements of glycogen.