Beef & eggs.....but powders is unflavored collagen. I can't remember exactly why it's important to maintain a proper methionine to glycine ratio, but I've read that methionine which meats are high in creates a larger need for glycine which collagen provides.....and may have positive effects on cholesterol(there's something to study).....like I said can't 100% remember but collagen or gelatin(same thing) has always been something I consume daily.