Do Extra Carbs Help to Build More Muscle in Trained Men
A crossover trial.
There is a longstanding belief in strength training circles that eating more carbohydrates fuels better performance and, over time, leads to more muscle and strength. Sounds like a plan, right? Carbohydrates are the body's preferred fuel source, and more fuel should mean more work done and more muscle built. Say no more! A new crossover trial published in Nutrients put that idea to the test in trained men, with results that challenge some common assumptions about carbohydrate intake and training adaptations.
Aims and Methods
The researchers wanted to know whether adding a modest amount of supplemental carbohydrate and the extra calories that come with it would improve muscle hypertrophy, strength, or fatigue resistance in men who were already trained and eating normally.
Twenty resistance-trained men with nearly a decade of training experience each took part in a double-blinded crossover trial. For eight weeks at a time, participants consumed either a daily protein-only supplement or a protein-plus-carbohydrate supplement, then switched to the other condition for another eight weeks. Both supplements contained the same amount of protein. The carbohydrate supplement added roughly 50 grams of maltodextrin on top of that. Participants continued their habitual training and diet throughout, without any instruction to change how they were already eating or lifting.
Outcomes measured before and after each phase included lean mass via dual-energy X-ray absorptiometry (DXA), muscle thickness and cross-sectional area via ultrasound, back squat one-repetition maximum (1RM), knee extensor peak torque, and a fatigue index measuring how much force participants lost during a set of repeated knee extensions. Training volume was also tracked throughout.
A crossover design was chosen specifically to improve statistical power, since it allows each participant to serve as their own control, which significantly reduces the noise introduced by individual differences in genetics, training history, and lifestyle.
Results
The carbohydrate supplement did what it was supposed to do nutritionally. Participants consuming it took in meaningfully more daily calories and more carbohydrates than during the protein-only phase. Protein and fat intake were the same across both conditions, and training volume did not differ either.
Despite that real dietary difference, none of the primary outcomes showed a meaningful difference between conditions. Lean mass, muscle thickness, vastus lateralis cross-sectional area, squat 1RM, peak torque, and fatigue index all improved similarly regardless of which supplement participants were using. Notably, the measures of muscle size and strength performance, if anything, trended slightly in favour of the protein-only condition, though not to a degree that was meaningful.
A sensitivity analysis looking at only the first phase of the study, before any potential carryover from the first intervention could influence the second, produced the same story. No significant differences between conditions.
The authors point out that standard resistance training does not deplete muscle glycogen to the degree that would be expected to impair performance. Research on glycogen depletion during typical lifting sessions suggests the reduction stays well below the threshold where it starts to compromise neuromuscular function. If glycogen is not getting low enough to matter, then topping it up more does not appear to change the training stimulus.
They also note that mechanical tension, not metabolic substrate availability, is the primary driver of muscle hypertrophy. When extra carbohydrates do not translate into more training volume, there is no clear mechanism by which they would drive more muscle growth.
Noteworthy
For intervention length, eight weeks is on the shorter end for detecting meaningful hypertrophy and strength changes, especially in trained individuals who adapt more slowly than beginners. Most well-designed resistance training studies use ten to sixteen weeks as a minimum to capture reliable adaptations, with twelve weeks being a commonly cited benchmark for hypertrophy research specifically.
For the sample size, twenty participants in a crossover trial is small. A crossover design does improve statistical power compared to a parallel group design, which is why the researchers chose it, but twenty is still a modest number. Parallel group studies typically aim for at least twenty to thirty participants per group to be adequately powered, and many researchers would consider forty or more per group a stronger standard for detecting smaller effect sizes.
The practical implication for readers is that null results from small, short studies should be interpreted as “we did not find an effect under these conditions” rather than “this definitively does not work.” Larger, longer, pre-registered trials with bigger dietary contrasts would be needed to draw firmer conclusions.
Practical Takeaways
For trained men who are already eating adequate protein and not in a calorie deficit, adding a moderate amount of extra carbohydrates through supplementation does not appear to meaningfully improve muscle growth or strength gains over eight weeks, according to this study.
The results apply specifically to trained men eating normal diets and performing conventional resistance training. The researchers are careful to note this should not be extrapolated to athletes in significant calorie deficits, those with very low baseline carbohydrate intake, or those performing high-volume training that genuinely depletes glycogen, such as endurance athletes or those with very high training frequencies per muscle group.
Protein intake matters. The research clearly supports adequate protein for muscle growth. Whether the extra calories and carbohydrates on top of that provide an additional benefit, in already-fed, already-trained individuals, is a much less clear story.
Being in a calorie deficit is a different situation entirely. The literature does support that energy restriction can impair lean mass gains. This study did not test that scenario. It was asking whether going above maintenance in carbohydrates provides an added benefit, and the answer here was no.
From a practical standpoint, if a trained person is already hitting their protein targets and training consistently, spending money on extra carbohydrate supplementation specifically to drive more muscle growth is not well supported by this data.
Reference
Henselmans M, Tiede DR, Plotkin DL, Mattingly ML, Harbour ER, Anglin DA, Fruge AD, Vårvik FT, Roberts MD, Izquierdo M. Effects of Modest Carbohydrate–Energy Supplementation on Resistance Training Adaptations in Trained Men: A Crossover Trial. Nutrients. 2026; 18(12):1961. https://doi.org/10.3390/nu18121961