If you eat fewer carbs, do your muscles grow less?

Short answer

No. In 11 studies that kept protein equal, the group eating more carbs did not grow more muscle. The smaller gains seen on keto included water stored in muscle, and the keto side, which lost more weight, also had 1.26 kg less lean mass.

If you eat fewer carbs, do your muscles grow less?
'Fewer carbs → less muscle growth': is this formula right?
A common claim is that you need lots of carbs, like rice and bread, to build muscle. Cutting carbs almost to zero on a keto diet brings the worry that muscles will stop growing. We checked studies that changed only the amount of carbs during training.
Changing only the carbs
The higher-carb side did not grow more muscle
A 2026 analysis pooled 11 studies with 229 people. Protein was kept equal, only carbs were set high or low, and people trained for 8.5 weeks on average. The higher-carb side did not grow more muscle, and the result did not change when only studies that also matched calories were looked at.
Adding extra carbs did not help either
Eating 485 kcal more a day: no difference in muscle thickness
20 people took turns, 8 weeks each, drinking a protein shake (4 g carbs) or a protein-and-carb shake (54 g carbs). During the carb shake period they ate 485 kcal more a day, but muscle thickness and size measured by ultrasound, and strength, showed no difference.
But keto studies seemed to show smaller gains
The weight they measured included water
In an 8-week study of 24 people eating plenty of calories, muscle mass rose 1.3 kg only on the regular diet and stayed flat on keto. Most keto studies measured whole-body lean mass (muscle and everything except fat). That weight includes carbs stored in muscle (glycogen) and the water bound to them.
When carbs came back, that weight came back
8% more in just 1 week
Over 10 weeks of training in 25 people, lean mass rose 2.4% on keto and 4.4% on the regular diet. In week 11, only the keto side went back to eating carbs, and lean mass rose another 4.8% in 1 week. The regular diet side did not change that week.
It is different when body weight drops
Keto had 1.26 kg less lean mass
An analysis that pooled 13 studies with 244 people found the keto side lost 3.67 kg more body weight and had 1.26 kg less lean mass. An analysis of 5 studies with 111 people and no planned calorie cut found no difference. That analysis judged keto hard to keep going past 8 weeks because it fills people up. To build muscle on keto, extra calories have to be added on purpose.
Summary: the amount of carbs was not what decided muscle
Get enough protein and total calories
With protein matched, the amount of carbs did not change muscle growth. The smaller numbers on keto included water stored in muscle, and the keto side, which lost more weight, also lost more lean mass. Even with fewer carbs, getting enough protein and total calories is what it takes.