Do You Need Carbs to Build Muscle? What the 2026 Crossover Trial Found in Trained Men

In this guide

1. The belief that carbs are "anabolic"

2. The crossover trial at a glance

3. Why a crossover design is powerful

4. What they found

5. The 485 extra calories that built nothing extra

6. The insulin argument, examined

7. What carbohydrates actually do for lifters

8. Who the result does and doesn't apply to

9. How many carbs should you eat?

10. The post-workout shake question

11. The bottom line

12. Frequently asked questions

Walk into any gym and you'll hear the same bit of folklore: protein builds muscle, but carbs "drive it in". The shake after a session is supposed to be 30 g of protein plus a pile of fast carbs, because insulin is meant to shuttle the amino acids into your muscles. It's tidy, it's plausible, and a 2026 randomised crossover trial suggests it's far less important than the supplement aisle implies, at least for well-trained men eating enough.

The study, from Menno Henselmans, Michael Roberts and colleagues, was published in Nutrients in June. We read the full open-access paper, including the limitations, and asked a practical question: if extra carbohydrate doesn't build extra muscle, what are carbs for in a lifter's diet?

The short version: in 20 resistance-trained men, eight weeks of a supplement containing 30 g of protein plus about 54 g of carbohydrate produced no significant differences in muscle size, lean mass, squat strength or knee-extension strength compared with eight weeks of 30 g of protein plus 4 g of carbohydrate, even though the carbohydrate version added about 485 kcal a day. It's a small trial in trained men training as usual, but it supports the view that carbohydrate isn't a hypertrophy "switch" once protein and calories are adequate.

The Belief That Carbs Are "Anabolic"

The idea has a respectable pedigree. Insulin is an anabolic hormone, carbohydrate raises insulin, and in the lab, high insulin reduces muscle protein breakdown. Add the observation that bodybuilders have long eaten a lot of rice and potatoes, and it's easy to conclude that carbs are a muscle-building nutrient. The difficulty is that "insulin does X in a test tube" isn't the same as "adding carbs adds muscle in a gym-goer".

The Crossover Trial at a Glance

Item	Details
Title	Effects of modest carbohydrate–energy supplementation on resistance training adaptations in trained men: a crossover trial
Journal and date	Nutrients, 18(12), 1961; June 2026 (Henselmans, Tiede, Plotkin, Mattingly, Harbour, Anglin, Fruge, Vårvik, Roberts and Izquierdo; doi:10.3390/nu18121961)
Participants	20 resistance-trained men (average age about 27; about 10 years of training experience)
Design	Quasi-randomised, double-blind, counterbalanced crossover: each man did both conditions for 8 weeks
Conditions	Protein-only supplement (30 g protein, 4 g carbohydrate) versus protein-plus-carbohydrate supplement (30 g protein, 54 g carbohydrate)
Context	Participants kept their habitual training and diet
Outcomes	DXA lean mass, ultrasound muscle thickness and cross-sectional area, back-squat one-rep max, fatigue index, knee-extension peak torque
Achieved difference	About +485 kcal a day and about +33 g of carbohydrate a day in the carbohydrate condition (the planned gap was about 50 g)
Result	No significant differences in any muscular adaptation; a non-significant trend in fatigue index (p = 0.097)

Why a Crossover Design Is Powerful

In most training studies, one group gets treatment A and another gets treatment B, and differences between people (genetics, training history, appetite) muddy the comparison. In a crossover trial every participant experiences both conditions, so each man is his own control. That makes small samples more informative, and it's especially useful in muscle research, where individual responses vary so much.

The study also used a double-blind design, so neither participants nor testers knew which supplement was which, and counterbalanced the order so that half did protein-only first and half did the carbohydrate version first. Those are strong safeguards for a supplement trial.

What They Found

Across eight weeks in each condition, the men gained comparable muscle and strength regardless of which supplement they took. There were no significant differences in lean mass, muscle thickness or cross-sectional area, back-squat strength or knee-extension torque. The authors summarised the results as most consistent with a null effect of additional carbohydrate–energy intake on hypertrophy and strength in well-trained men in this setting.

Two details are worth noting. Training volume, protein intake and fat intake didn't differ between conditions, so the comparison was reasonably clean. And adherence to the protein-only supplement was lower than to the carbohydrate one, which tells us something about palatability and satisfaction: people liked the carb shake more.

The 485 Extra Calories That Built Nothing Extra

The achieved carbohydrate difference was about 33 g a day, smaller than planned, but the total energy difference was meaningful: roughly 485 kcal more per day in the carbohydrate condition. That's a moderate surplus over eight weeks, and it produced no significant extra muscle or strength. It echoes what we say in our bulking calorie guide: in trained lifters, a larger surplus doesn't build proportionally more muscle, because there's a ceiling on how fast muscle can grow. Check the full paper for fat-mass changes, which we haven't seen reported in the summaries.

The Insulin Argument, Examined

The theory says carbs raise insulin, insulin blocks muscle breakdown and so more muscle is retained. Parts of it are true in isolation. But in humans who already have adequate protein, studies such as Greenhaff and colleagues' (2008) have found that raising insulin adds little to muscle protein synthesis, and the main effect of insulin is to reduce breakdown, which is already low after a training-day protein meal. Protein itself does the heavy lifting by supplying amino acids and, through leucine, switching on the muscle-building pathway.

That doesn't mean insulin is irrelevant, only that in well-fed, trained people the marginal benefit of extra carbohydrate-driven insulin appears small. The new trial fits that picture.

What Carbohydrates Actually Do for Lifters

Saying carbs aren't a growth switch isn't the same as saying they're useless. They matter in other ways:

• Training fuel. Muscle glycogen powers hard sets. In high-volume sessions, two-a-days or long workouts, low glycogen can reduce performance. The non-significant fatigue-index trend in this trial hints at that, though it didn't reach significance.
• Energy for a surplus. If you struggle to eat enough, carbohydrates are an easy way to add calories without much fullness.
• Protein sparing. When carbs are adequate, less protein is burned for energy.
• Adherence and mood. Many people simply train and feel better with enough carbohydrate, and in this trial participants took the carbohydrate shake more consistently.
• Calorie deficits. In a deficit, adequate carbohydrate helps preserve training quality, which indirectly protects muscle.

Who the Result Does and Doesn't Apply To

Question	What this trial says
Trained men, moderate extra carbs, normal training?	No extra hypertrophy or strength over eight weeks
Beginners?	Not tested; newer lifters respond to almost any adequate stimulus
Women or older adults?	Not tested
Low-carb or keto dieters?	Not tested; participants kept their habitual diets, not a very low-carb one
Calorie deficit?	Not tested; the study was outside a deficit, so the authors caution against generalising
Endurance or very high-volume training?	Not tested; glycogen needs rise with volume
Longer than eight weeks?	Unknown

Other limitations include the small sample, a carbohydrate contrast smaller than intended, and baseline diets that weren't controlled. A false negative can't be ruled out for small effects.

How Many Carbs Should You Eat?

For most lifters, carbohydrate should fill the calories left after protein and fat. A common sports-nutrition range for strength athletes is roughly 4–7 g per kg of body weight a day, adjusted for training volume and goals. Protein is the nutrient to prioritise, about 1.6–2.2 g/kg, as covered in our protein sources guide.

Goal	Protein	Carbohydrate approach
Lean bulk	1.6–2.2 g/kg	Moderate to high (about 4–7 g/kg) to fuel training and fill a small surplus; see our lean-bulk plan
Maintenance	1.6–2.0 g/kg	Moderate (about 3–5 g/kg), scaled to training load
Fat loss	1.8–2.4 g/kg	Lower but enough to train well; most of the deficit can come from carbs and fat
Low-carb preference	1.6–2.2 g/kg	Works for many, with a possible performance cost in high-volume work

Use the macro calculator, TDEE calculator and protein intake calculator to set your numbers, and track strength with the one rep max calculator.

The Post-Workout Shake Question

Should you add carbs to your post-workout shake? If you enjoy it, it helps you hit calories, or you train twice a day, sure. If you're not trying to refuel for another session soon and you're eating enough overall, this trial suggests you won't build more muscle by adding them. A protein-only shake plus a normal meal is perfectly fine. We discuss timing in more detail in our guide to pre- and post-workout nutrition.

The Bottom Line

This is a well-designed, small crossover trial finding that in trained men eating normally and training as usual, an extra ~50 g of carbohydrate (and about 485 kcal a day) didn't increase muscle growth or strength over eight weeks. It supports an old principle that's easy to forget in supplement marketing: protein and total training stimulus drive hypertrophy, and carbohydrate is mainly fuel and convenience.

So eat enough protein, make sure you're not under-fuelling, let carbs fill the rest according to your training and preferences, and stop worrying that skipping the carb half of the shake is costing you muscle. The things that move the needle are still sets, progression, protein, calories and sleep.

Frequently Asked Questions

Do carbs build muscle?

Not by themselves. In a 2026 crossover trial of 20 trained men, adding about 50 g of carbohydrate (and roughly 485 kcal a day) to a protein supplement for eight weeks didn't significantly increase muscle size, lean mass or strength. Carbohydrate mainly fuels training.

Do I need carbs in my post-workout shake?

Not for muscle growth, based on this trial. They can help if you need calories, want to refuel quickly for another session, or simply enjoy them.

Is insulin important for muscle growth?

Insulin reduces muscle protein breakdown, but when protein intake is adequate, extra insulin adds little to muscle protein synthesis in healthy adults. Protein and leucine are the main drivers.

How many carbs do lifters need?

A common range for strength athletes is roughly 4–7 g per kg of body weight daily, adjusted for training volume and goals. Prioritise protein first, then fill the remaining calories with carbohydrate and fat.

Does this mean low-carb diets are fine for building muscle?

The trial didn't test low-carb diets, so it can't say. Many people build muscle on lower-carbohydrate diets, but very low carbohydrate intake may hurt performance in high-volume training.

Did the study show carbs don't matter at all?

No. It showed no extra hypertrophy or strength from a modest carbohydrate increase in trained men outside a calorie deficit over eight weeks. Carbohydrate still matters for training performance, energy and adherence.

Would the result differ for beginners or women?

Possibly. The study only included trained men. Beginners respond to almost any adequate stimulus, and women and older adults weren't studied.

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References & Sources

1. Henselmans, M. et al. (2026). Effects of modest carbohydrate–energy supplementation on resistance training adaptations in trained men: a crossover trial. Nutrients, 18(12), 1961. doi:10.3390/nu18121961; PMC13305566.
2. ClinicalTrials.gov NCT07600138. Effects of carbohydrates versus carbohydrates plus protein on resistance training outcomes.
3. Greenhaff, P. L. et al. (2008). Disassociation between the effects of amino acids and insulin on signaling, ubiquitin ligases, and protein turnover in human muscle. American Journal of Physiology: Endocrinology and Metabolism, 295(3), E595–E604.
4. Morton, R. W. et al. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength. British Journal of Sports Medicine, 52(6), 376–384.
5. Thomas, D. T., Erdman, K. A. & Burke, L. M. (2016). Nutrition and athletic performance. Medicine & Science in Sports & Exercise, 48(3), 543–568.
6. MacrosMeasure (2026). Free Macro Calculator.