For building muscle over weeks, it does not seem to matter much: in a 12-week trial, young adults who lifted after an overnight fast gained muscle and strength similar to those who ate 1 to 2 hours before4. Within a single session, though, a meal tends to help you do more work, especially after a long overnight fast3.
So the answer depends on the question. Long-term gains and one day's performance are measured differently, and the studies give different answers.
Two different questions
- Adaptation: does training fasted change how much muscle and strength you gain over weeks? This needs training trials.
- Performance: does eating first change how many reps or sets you can do today? This needs crossover studies, where each person trains both fed and fasted.
In these studies, fasted means lifting after an overnight fast, before any food that day. Fed means lifting after a meal, usually with carbohydrate.
What the training trials found
In a 2025 randomised trial, 28 young adults trained twice a week for 12 weeks4. Fifteen trained after an overnight fast. Thirteen trained 1 to 2 hours after a carbohydrate-rich meal. Both groups got the same (isocaloric) nutrition guidance.
| Outcome | Fasted group | Fed group |
|---|---|---|
| Quadriceps muscle thickness | +1.21 cm | +1.18 cm |
| Knee extension 1RM | +28.53 kg | +29.31 kg |
| Bench press 1RM | +10.53 kg | +4.89 kg |
Both groups improved on every measure, and none of the differences between groups was statistically significant4. 1RM is a one-rep max, the heaviest weight lifted once. The bench press gap looks large, but in a group of 13 to 15 people it was within the range chance could produce.
Strength gain over 12 weeks: fasted vs fed lifting · kg
Fasted Fed
The same research group pooled the available trials in a 2025 meta-analysis, a study that combines trials into one estimate5. It found only 4 trials. There were no significant differences between fasted and fed training in fat-free mass, muscle size or strength, though the confidence intervals were wide. One outcome did differ: body fat mass changed more with fasted training (standardised difference −1.00, 95% CI −1.97 to −0.03). Three of the four trials were rated at high risk of bias, meaning their design could have skewed the result.
In plain terms: the few trials that exist found fasted and fed lifters built muscle and strength alike.
What happens within a session
Here the picture changes. A 2022 meta-analysis pooled 21 crossover studies with 226 people, comparing carbohydrate with a placebo or water before or during resistance exercise3. Carbohydrate raised total training volume, the total weight lifted across the session, with a standardised effect size of 0.61. An effect size compares a difference with how much people normally vary; 0.5 is conventionally moderate.
The benefit depended on the session3:
- Longer sessions. In sessions over 45 minutes the effect size was 1.02.
- Longer fasts. After 8 or more hours without food it was 0.39.
- More hard sets. The more sets taken to maximal effort, the larger the benefit.
Effect of carbohydrate on session training volume · effect size
A 2019 study shows what this looks like in practice2. Sixteen resistance-trained men who normally ate breakfast lifted twice, in random order: 2 hours after a typical carbohydrate breakfast, or 2 hours after a water-only breakfast. They did four sets to failure of back squat and bench press.
Total reps in four sets to failure: no breakfast vs breakfast · reps
Water-only breakfast Carbohydrate breakfast
Without breakfast they completed 58 squat reps against 68, and 38 bench press reps against 402.
In plain terms: eating before lifting tends to let people do more work in that session, most after a long fast and in longer sessions.
Why the two answers do not clash
More reps in one session does not automatically become more muscle over months. The 12-week trial trained twice a week, which is modest volume; the fasted group may have done slightly less work per session without it showing in the results4. The trial did not report session volume in its abstract, so this is our reading, not a measured result.
Protein fits into the same picture. In a 10-week trial of 21 trained men, one group took 25 g of protein just before training and then waited at least 3 hours to eat; the other trained after at least 3 hours without food and took the protein right after. Both groups gained similarly1. The authors suggest that what matters is the gap between the meal before training and the meal after it. That is covered in the companion piece on whether the anabolic window is real.
What this means in practice
The studies describe choices, not rules:
- If you lift well fasted, the training trials found similar long-term gains45.
- If sessions are long or include many hard sets, the performance studies found carbohydrate beforehand helped volume, especially after an overnight fast3.
- Timing of the meal before. In the studies, fed sessions came 1 to 2 hours after eating42.
What people eat across the day still sets the totals the trials held constant; see how much protein per kg and how many carbs per day. People with diabetes or another medical condition have separate considerations around exercise and meals, and those are a question for their doctor.
What the studies found
| Study | Who was studied | Key result | Year |
|---|---|---|---|
| Schoenfeld et al., *PeerJ*1 | 21 trained young men, 10 weeks | Protein just before vs just after training (3-hour gap either side): similar gains | 2017 |
| Bin Naharudin et al., *J Strength Cond Res*2 | 16 trained men, crossover, one session each | Water-only breakfast: fewer reps (squat 58 vs 68; bench 38 vs 40) | 2019 |
| King et al., *Sports Med*3 | Meta-analysis of 21 crossover studies, 226 people | Carbohydrate raised session volume (effect size 0.61), most in sessions over 45 minutes | 2022 |
| Vieira et al., *IJSNEM*4 | 28 young adults, 12 weeks, twice a week | Fasted vs fed: similar gains in muscle thickness and strength | 2025 |
| Vieira et al., *J Bodyw Mov Ther*5 | Meta-analysis of 4 trials in adults | No significant difference in lean mass, muscle size or strength; greater fat-mass change when fasted | 2025 |
Limits worth knowing
- Very few training trials. Four in the 2025 meta-analysis, three at high risk of bias5.
- Small and short. 28 people over 12 weeks in the trial, training twice a week.
- Same group. The 2025 trial and review come from the same research group; the review abstract does not say whether it includes their own trial.
- Performance is not muscle. The session studies measured reps and volume on one day, not gains over months.
- Mostly young men. The session studies were largely in young men who lift.
- Abstract only. We read both 2025 papers, the 2019 study and the 2022 meta-analysis as abstracts; the 2025 papers are paywalled. Only their stated numbers are used.
Latest research
The newest papers we opened are the 2025 trial and the 2025 meta-analysis from the same group45. Together they say that for muscle and strength over 12 weeks, lifting after an overnight fast and lifting after a meal gave similar results. Neither measured how much work was done per session, which is where the older crossover studies found a difference. A trial that tracks both, session volume and long-term gains, in people training more often would answer the question properly.
The short version
- Over 12 weeks, fasted and fed lifters gained similar muscle and strength in the few trials that exist.
- Within a session, carbohydrate beforehand let people do more total work, most after long fasts and in longer sessions.
- The meal before and the meal after a workout matter more as a pair than either one alone.
- Whether to eat first is a performance and comfort choice more than a muscle-building one.
Educational overview only — not medical advice.
