A quick look at the best weight gain supplements. Best vegan: IronVegan Athlete’s Gainer. Best carbohydrate-only powder: NOW Sports Carbo Gain Powder. Best without artificial ingredients: True.

Like the best protein shakes, mass gainers (also known as weight gainers or gainer shakes) are full of muscle-building amino acids and protein, but they also add carbs and other nutrients to maximize your calorie and macro intake. Adding a high-quality mass-gainer powder can make a huge difference in your bulking regimen.