Short answer: no. Carbs don’t build muscle by themselves. Protein, hard training, and enough total calories do that. Carbs are fuel, and fuel matters, but a new study just showed what happens when you add a pile of carbs on top of an already solid setup: nothing extra.
The study
Researchers ran a quasi-randomized, double-blinded, counterbalanced crossover study, published in Nutrients in June 2026. Twenty resistance-trained men, average age 27 with about 10 years of lifting experience, did 8 weeks on each arm of the study.
Both groups got a post-workout shake with 30 grams of protein. The only difference was the carbs in the shake: one shake had 54 grams, the other had just 4 grams. Same training, same protein. The carb shake was the only variable.
What happened
The high-carb group ate 485 more calories per day on average. And still, there was no significant difference in:
- Lean mass (measured by DXA scan)
- Muscle thickness and cross-sectional area (ultrasound)
- Back-squat 1-rep max
- Fatigue index
- Knee-extensor peak torque
More carbs, more calories, same muscle, same strength. That’s the headline, and it’s real.
The catch nobody mentions
Here’s the part that keeps this honest. Even though the shakes differed by 50 grams of carbs, the guys’ total daily carb intake only differed by about 33 grams. People compensate. Give someone a heavy shake and they eat a little less the rest of the day without thinking about it.
So this study isn’t really “high-carb diet vs low-carb diet.” It’s “a high-carb shake vs a low-carb shake, inside real diets that mostly evened out.” That’s still useful, but it’s not the knockout blow some headlines will make it.
Second caveat: the sample is trained men only. Twenty of them. That’s a solid design for that group, but it doesn’t automatically speak for beginners, women, or people cutting weight.
Who still needs carbs
Carbs aren’t useless. They’re just not magic. You want plenty of them if:
- You struggle to eat enough. Carbs are the easiest calories to get down. This is where a high-carb shake actually earns its place.
- Your training volume is high. Long sessions, two-a-days, or conditioning on top of lifting. Depleted lifters perform worse.
- Your top sets are fading. If your food is low and performance is dropping, carbs are the first lever to pull.
Your move
- Hit your protein every day. That’s the part that did the work in this study.
- Track total calories. If you’re not gaining, you’re not eating enough overall, not missing one macro.
- Add carbs when performance or appetite demands it, not because a label promises gains.
Volume does the work a shake can’t. If your training isn’t sorted yet, here’s how many sets per week actually build muscle.
Carbs are fuel. Get enough to train hard, get your protein in, and stop expecting a shake to do the program’s job.
Source: the full study is available as a PDF from Nutrients, June 2026.