It depends. “What happens at the muscle level is going to greatly depend on the timing of the alcohol ingestion,” says Evelyn Parr, a Ph.D. candidate in exercise and nutrition at Australian Catholic University. If you’re lifting in the morning and drinking beer in the evening, you should be OK on strength gains. (Assuming you’re eating healthy generally.) If you’re drinking the beer within an hour or two of your lift, it’s a hazier outlook, because there may be a chance of reduced protein synthetic response (that is, muscle building).
But will it add fat? Not likely, unless you really hit the bottle. “If your energy intake (the amount you drink) is greater than your energy expenditure, then the increased daily intake will induce weight gain,” says Parr. In other words: If “one” beer is what we’re talking about, you’re fine.