['Homemade Protein Smoothies. Drinking homemade protein smoothies can be a highly nutritious and quick way to gain weight. ... ', 'Milk. Milk has been used as a weight gainer or muscle builder for decades ( 1 ). ... ', 'Rice. ... ', 'Nuts and Nut Butters. ... ', 'Red Meats. ... ', 'Potatoes and Starches. ... ', 'Salmon and Oily Fish. ... ', 'Protein Supplements.']