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.

If young guys lift weights hard and do intense workouts while eating less for a month, chugging 2.4 grams of protein per pound of muscle each day helps them gain more muscle and lose more fat than eating half that much protein.

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.

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.

If you're lifting weights and want to build muscle, eating at least 1.6 grams of protein per kilogram of body weight every day is the biggest factor that helps — more protein means better results, and when you eat it doesn't matter as much.

If young guys eat more protein while working out hard and cutting calories for a month, they’ll gain more muscle and lose more fat compared to eating less protein.