When you’re after muscle growth, you need two things: lots of protein and lots of calories. By consuming protein, you supply your body with amino acids, branched-chain amino acids (BCAAs) in particular. These molecules are the building blocks that create your muscles. They’re also needed to repair muscle damage inflicted during intense workouts.
Amino acids serve one more purpose: fuel. When your body runs out of calories from food, it can start to consume its own muscle. This is why, to maximize muscle building, it’s necessary to increase both calorie and protein intake. You want to make sure you’re building as much muscle as you can while avoiding burning it for energy.
Most of the calories in general-purpose whey protein supplements usually come from the protein. This is good if you’re trying to get lean. But when your goal is to gain muscle mass, you’re going to need a protein powder with more calories from carbohydrates and fat.