What It is
Stock is what you get after boiling bones in hot water for an extended period of time. When we say you should eat the entire animal, we really mean the entire animal, and that includes the bones. But we don’t want you to break your teeth, so boiling them into stock or bone broth is usually the way to go.
After letting the bones simmer in water for several hours and removing the bones, what you’re left with is stock that contains a slew of nutrients you can’t get anywhere else. Chief among them is gelatin: an important nutrient for building and maintaining strong bones and teeth. Most people don’t get enough gelatin in their diet and regularly incorporating stock into your diet (whether cooking with it or just drinking it straight) is probably the best way to get that gelatin.
Mark Sisson talked about the various nutrients and health benefits of bones, as well as the best ways to incorporate them into your diet.