Does alcohol affect muscle growth?
Yes, in quantity: a heavy session after training cut muscle protein synthesis by roughly a third, on top of the calories it adds.
The study that gets quoted used about twelve drinks, which is a night out rather than a beer. At that dose the muscle building response after training dropped sharply, and adding protein did not fully rescue it.
Two or three drinks on a weekend will not undo your training. What it does do is add calories you did not plan, make the next day’s session worse and cut into your sleep, which is the part most people underrate.
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- Parr, E.B. et al. (2014). Alcohol ingestion impairs maximal post-exercise rates of myofibrillar protein synthesis following a single bout of concurrent training. PLoS One 9(2). 8 men, about 12 drinks after training: muscle protein synthesis fell clearly compared with protein alone, even when protein was taken alongside the alcohol.
- Hall, K.D. et al. (2012). Energy balance and its components: implications for body weight regulation. Am J Clin Nutr 95(4). The second cost: alcohol carries 7 kcal per gram and rarely replaces other food.