Keep carbs up enough to fuel hard days while cutting
Cutting carbohydrate too low while dieting impairs hard workouts and muscle retention, so keeping enough carbohydrate protects training quality during weight loss.
In plain English
Dropping carbs too low while cutting makes hard runs and lifts suffer and makes muscle harder to keep. Enough carbohydrate to fuel the hard days protects both.
Why it works
Low carbohydrate availability increases the breakdown of amino acids for fuel and limits the signaling that builds and retains muscle, while also impairing high-intensity output.
What it means in practice
Tell cutting runners to take the deficit mostly from fat and to keep carbohydrate high enough to fuel their hard sessions, rather than cutting carbohydrate to the floor.
The evidence
-
Low carbohydrate availability increases amino-acid oxidation, limits the muscle-building response to resistance training, and impairs high-intensity and anaerobic performance, even when maximal strength is less affected. The review suggests athletes who need to train hard should avoid restricting carbohydrate too far.
-
Recommends losing about 0.5-1.0% of body weight per week, with more conservative deficits as the athlete gets leaner. Protein of roughly 2.3-3.1 g/kg of fat-free mass per day (about 1.6-2.4 g/kg body weight) is advised, with carbohydrate set to support training (about 2.5 g/kg/day or more) and fat kept above roughly 0.5 g/kg/day.
Why we call confidence medium
Mechanistic and review evidence shows low carbohydrate availability raises amino-acid oxidation, blunts the muscle-building response, and impairs high-intensity performance. Most of the evidence is short-term or mechanistic rather than long field trials.
Where it applies
Runners and athletes dieting while training with meaningful intensity.
Does not apply to: low-intensity or low-volume training, where carbohydrate needs are modest.
Last reviewed 2026-06-20. See how we score.