Yes, in the trials so far. Trained lifters who ate all their food within an 8-hour window gained as much fat-free mass over 12 weeks as lifters who ate at any time of day, and they gained less fat1. The catch is that most of these trials are small and short, and the window seems to work mainly by changing how much people eat.
This article covers what the trials compared, what they found for muscle, fat and strength, and why the timing itself may matter less than it looks.
What was studied
Intermittent fasting means limiting when you eat rather than what you eat. The version tested most with lifting is time-restricted eating (TRE): all food inside a daily window, often 8 hours, with 16 hours of fasting. That is the "16:8" pattern.
Fat-free mass is everything in the body that is not fat: muscle, water, bone and organs. Most trials measure it, not muscle alone. A surplus (or "bulk") means eating more energy than you use, which is how most lifters try to add muscle.
The key trial for this question is a 2026 randomised trial from Germany1:
| What | Detail |
|---|---|
| People | 23 resistance-trained adults (17 men, 6 women), average age about 30 |
| Length | 12 weeks, full-body training 3 times a week |
| Both groups | told to eat 300 to 500 kcal a day above their estimated needs, with protein and fat targets |
| Window group | all food between 12:00 and 20:00 (16:8); training inside the window |
| Control group | the same targets, no time limit |
| Body composition | single-frequency bioimpedance (a small electric current through the body) |
In plain terms: two groups of trained lifters, both trying to eat in a surplus, one of them inside an 8-hour window.
What the studies found
Muscle held up. Fat-free mass rose by a group average of 1.34 kg in the window group and 1.38 kg in the control group, with no significant difference1. The device's muscle-mass estimate rose by 1.07 and 1.13 kg. Strength gains matched too: deadlift one-rep max (the heaviest single lift) rose about 26 kg in both groups on average.
Fat did not. The window group gained 2.00 kg of fat on average; the control group gained 4.38 kg (p = 0.009)1. That is less than half.
Change over 12 weeks, 16:8 window vs eating at any time · kg
16:8 window Any time
Why: they ate less. The window group's planned intake was about 2,993 kcal a day; its logged intake was about 2,567, significantly below plan1. For the control group the figures were 3,114 planned and 2,987 logged. The window group also ate fewer meals, 2.24 a day against 3.41. Even so, the difference in energy intake between the two groups was not statistically significant (p = 0.092), so the fat result rests partly on a trend.
Earlier work points the same way. A 2016 trial of 34 resistance-trained men compared an 8-hour window with a normal schedule at matched energy for 8 weeks: fat-free mass, arm and thigh muscle area and maximal strength were maintained in both groups, and fat mass fell more with the window; testosterone and IGF-1, a growth-related hormone, fell in the window group only3. A 2021 meta-analysis of 8 studies and 221 people found intermittent fasting plus resistance training lowered fat mass by 1.36 kg on average versus normal eating, with no significant effect on fat-free mass5. A 2026 meta-analysis of 8 randomised trials in resistance-trained people found the same pattern6.
Intermittent fasting vs normal eating with resistance training, pooled differences · kg
In plain terms: in these trials, the window did not cost muscle, and it tended to cost less fat, mainly because people ate less.
Where fasting did cost something
Two trials found a price, and both are worth knowing.
In a 2017 trial of young, recreationally active men, a much tighter pattern (all food within 4 hours, 4 days a week) cut intake by about 650 kcal on those days4. Muscle cross-sectional area grew in both groups. By effect size, though, the group that ate normally gained more lean soft tissue (+2.3 kg, d = 0.25, a small effect), while strength gains favoured the fasting group.
In a 2025 trial, 17 well-trained men and women ate a 10% surplus with high protein for 8 weeks2. The window group ate within 8 hours that started at least 1 hour after training, so they trained fasted. Calories did not differ between groups. The results:
- Fat-free mass rose in both groups with no between-group difference2.
- The window group gained 1.4 kg less fat on average (95% CI -2.5 to -0.3)2.
- The window group did fewer total reps over the 8 weeks: 6,960 against 7,334, about 5% fewer2.
- Squat one-rep max rose about 4.2 kg less in the window group (95% CI -8.2 to -0.2); bench press did not differ2.
- The window group also rated their daily energy lower at week 42.
The 2026 trial, where training sat inside the eating window, found no strength cost1. Its authors note their result "cannot be generalized to fasted training conditions". So training fasted and eating in a window are different things, and the second may be easier on performance than the first.
In plain terms: a very tight window can make eating enough hard, and training fasted may trim the work you get done.
What the window does and does not do
The authors of the 2026 trial are careful here. They write that their findings "do not necessarily indicate that TRE itself confers a unique physiologic advantage", and that "similar outcomes may theoretically be achievable with non-TRE approaches if a more moderate caloric surplus is prescribed"1.
They also note that the control group's larger surplus did not add more muscle: "higher energy and protein intake were not associated with additional increases in fat-free mass or muscle mass"1. The extra food mainly went to fat.
That is the real lesson. In these trials, what drove muscle was training plus enough protein and energy. What drove fat was how far above maintenance people ate. The clock mostly changed the second. For how a surplus is sized, see how many calories should I eat; for protein, how much protein per kg. A related question, whether carbohydrate itself matters for muscle, is covered in our article on whether you need carbs to build muscle.
The studies at a glance
| Study | Who was studied | Key result | Year |
|---|---|---|---|
| Moro et al., *J Transl Med*3 | 34 resistance-trained men, 8 weeks, 8-hour window, energy matched | Fat-free mass, muscle area and strength maintained; fat mass fell more with the window | 2016 |
| Tinsley et al., *Eur J Sport Sci*4 | Young recreationally active men, 8 weeks, 4-hour window on 4 days a week | Intake about 650 kcal lower on fasting days; muscle area grew in both; lean tissue gain favoured normal eating by effect size | 2017 |
| Ashtary-Larky et al., *Physiol Behav*5 | 8 studies, 221 people doing resistance training | Fat mass -1.36 kg vs normal eating; fat-free mass no significant difference | 2021 |
| Blake et al., *J Int Soc Sports Nutr*2 | 17 well-trained men and women, 8 weeks, 10% surplus, trained fasted | Fat-free mass similar; 1.4 kg less fat; about 5% fewer total reps; smaller squat gain | 2025 |
| Gavanda et al., *J Nutr*1 | 23 trained lifters, 12 weeks, surplus, 12:00–20:00 window | Fat-free mass +1.34 vs +1.38 kg; fat +2.00 vs +4.38 kg; strength similar | 2026 |
| Ali et al., *Nutr Res*6 | 8 randomised trials, resistance-trained people | Fat mass -1.25 kg; fat-free mass no significant difference | 2026 |
Limits worth knowing
- Small and short. The single trials with a stated size had 17 to 34 people and ran 8 to 12 weeks. A small difference in muscle would be hard to detect.
- Indirect measures. The 2026 trial used single-frequency bioimpedance, which estimates muscle from how a current moves through the body1. The 2025 trial used a body-volume and body-water model and dropped its planned ultrasound2.
- No equivalence test. The 2026 trial did not formally test whether the groups were the same, only whether they differed1. "No significant difference" is not proof of no difference.
- Self-reported intake. Both surplus trials relied on food logs, which are known to be imprecise.
- Numbers that do not line up. The 2025 paper's abstract, results and discussion give different per-group fat-free and fat mass figures; we use only its results-section comparisons2.
- Abstract only for the 2016, 2017, 2021 and 2026 meta-analysis papers. We read the 2026 trial and the 2025 trial in full.
- Funding. The 2026 trial reports no funding1.
Latest research
The newest trial here, published in July 2026, is the first to test a 16:8 window during a planned surplus over 12 weeks1. It found muscle and strength gains held and fat gain was smaller, largely because the window group ate less than planned. The 2026 meta-analysis of 8 trials in resistance-trained people reached a compatible conclusion and said its findings should be read with caution because the trials are few, small and short6. When a larger or longer trial appears, this page will be updated and its date will change.
The short version
- In trials so far, lifters eating in an 8-hour window gained or kept as much fat-free mass as normal eaters.
- The window tended to mean less food, and so less fat gain.
- Training fasted, or a very tight window, came with fewer reps and smaller lower-body strength gains in some trials.
- The authors say the timing itself may not be the reason; a smaller surplus may do the same.
- The trials are small and short, so the certainty is limited.
Educational overview only — not medical advice.
