What Is Whey Protein? Benefits, Types, and How to Use It (Full Guide) Whey protein  is one of the most popular fitness supplements  in the world — and for good reason. It’s a high-quality, fast-digesting protein  that supports muscle growth , post-workout recovery , and overall sports nutrition , making it ideal for beginners and advanced athletes alike. Where Does Whey Protein Come From? Whey is a natural by-product of cheese production . When milk separates, it forms: Curds