Protein—it’s the macronutrient that every serious lifter places the most importance on, and for good reason. Research confirms that eating as much as 1.5 grams of protein per pound of body weight has a significant impact on muscle building, and protein supplements ensure that you get the right kinds of proteins. The problem is that with so many choices, it’s tough to know which product to buy. Answer these seven simple questions to figure out which is best for you.