Does Intermittent Fasting Hurt Your Gains?

Intermittent fasting and building muscle have always had an awkward relationship in gym culture. The concern makes sense on paper: if you're only eating within an 8-hour window, can you actually get enough calories and protein in to support real growth, especially during a bulk, when the whole point is eating more than you're used to? A direct 2026 trial finally tested this in the exact scenario lifters actually worry about, and the answer is more interesting than a simple yes or no.

The direct test: fasting during an actual bulk

A 2026 randomized controlled trial put 23 resistance-trained people through 12 weeks of serious training (3x/week), split into a 16:8 time-restricted eating (TRE) group and an unrestricted control group, both instructed to eat 300-500 kcal above maintenance [1]. This wasn't fasting during maintenance or a cut, it was fasting layered directly onto a bulking phase, the exact combination most lifters assume doesn't work.

Muscle mass and strength gains came out essentially identical between groups. Fat-free mass increased by about the same amount in both (TRE: +1.34 kg, control: +1.38 kg), and both groups added the same weight on deadlift (+26 kg) and bench press (roughly +12-13 kg). Fasting didn't blunt growth.

The honest twist: it wasn't the fasting itself doing the work

Here's the part worth actually paying attention to. The TRE group didn't hit their prescribed surplus. They were told to eat 300-500 kcal above maintenance, same as control, but actually ate significantly less than that target, and less protein too (1.44 g/kg vs. control's 1.60 g/kg, still a solid number, just lower). The control group, eating on a normal schedule, stuck closer to the prescribed surplus and ended up gaining significantly more body weight and fat mass than the TRE group did.

So TRE didn't have some special muscle-preserving property. The restricted eating window just made it physically harder to eat as much food, which meant a smaller real surplus, and a smaller surplus is already known to produce less fat gain without costing muscle, as long as protein and training stay adequate. That's consistent with an existing finding already on this site: Helms et al. 2023 found a moderate surplus builds the same muscle as a large one, the large surplus just adds more fat. This new study is effectively a real-world version of the same lesson, just arrived at by accident through a fasting protocol instead of on purpose through calorie counting.

Does this hold up across more studies?

A separate 2026 meta-analysis pooled 11 studies (303 participants, protocols mostly time-restricted eating, 4 weeks to 12 months) comparing intermittent fasting plus resistance training against resistance training alone [2]. The result matches the single trial above: no clear difference in maximal strength, muscular endurance, hypertrophy-related outcomes, or explosive performance between fasting and non-fasting lifters. The authors were careful to frame this as a directional finding, not a settled one, only 11 studies exist on this specific comparison so far.

Where that leaves you

Intermittent fasting doesn't appear to hurt muscle or strength gains, including during a bulk, as long as you're still getting enough protein and calories in within your eating window. But the RCT above is also a real warning: a restricted window can make it genuinely harder to actually hit a surplus, which in this study happened to work out fine (less fat, same muscle), but wouldn't be fine if it pushed protein intake too low or created too large a deficit. If you're fasting and bulking, the real thing to track isn't the fasting protocol itself, it's whether you're still actually hitting your numbers inside the window you've got.

Full details on both studies are in the Research Library.

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References

1. Gavanda, S., Arnet, L., Löffler, D., Dissemond, J., Havers, T., Wiewelhove, T., Geisler, S., Held, S., Brinkmann, C., & Isenmann, E. (2026). Time-Restricted Eating during a Bulking Phase Is Associated with Reduced Fat Accumulation, while Muscle and Strength Gains Are Maintained: A 12-Wk Randomized Controlled Trial. The Journal of Nutrition, 156(9), 101722.
2. Zhang, M., Wang, S., Wutichat, S., Tanphanich, T., Li, H., & Zhang, X. (2026). Effects of Intermittent Fasting Combined with Resistance Training on Training Adaptations: An Exploratory Multilevel Meta-Analysis. Frontiers in Nutrition, 13, 1879031.

Full details and direct links for both are in the Research Library.