R1 Gain By Rule One Proteins is the best product specifically for gaining LEAN muscle mass. Most other mass gainers add unnecessary ingredients in them that actually make you gain weight, but it will not be the lean muscle mass you are hoping for. When taking R1 Gain, you will not gain any excess fat that other products will cause you to gain. The reason for this is simple. R1 Gain contains 75 grams of carbohydrates per serving and 50 grams of protein per serving, which makes for a PERFECT proportion of carbohydrates to protein for those looking to gain lean muscle mass. The carbohydrates to protein ratio is 1.5 to 1.