When it comes to weight gain you need all of your macros not just protein. While protein is absolutely critical for weight gains the right ratio of high quality-healthy carb and fat sources is just as important. With a purposefully crafted macronutrient breakdown that contains quality protein carbohydrates and fats cor-performance gainer will help you build lean muscle mass. When to take cor-performance gainer: you want to build lean muscle mass. You want a high quality healthy source of protein fat and carbohydrates.