Protein supplements might give athletes a small boost in endurance, especially when taken with carbs—but it could just be because they're eating more calories overall.

Taking about an extra gram of protein per pound of body weight every day — mostly from supplements — might help athletes perform their best, but it's hard to be sure because most studies don’t account for total calories.

Athletes taking protein might get stronger, but it could just be because they're eating more total calories — not because of the protein itself.

Protein supplements might help your muscles refill energy faster after a workout compared to just carbs — but it could just be because they add extra calories, not because protein itself speeds up recovery.

Adding protein to carbs and water doesn’t really help or hurt your workout performance if you're already getting the same amount of energy.

Taking protein supplements for several weeks might help athletes perform better than taking them just once, but we’re not totally sure because the studies didn’t control for total calorie intake.