Bone is composed of a matrix that includes collagen, protein and mineral deposits, including calcium and phosphate, and provides gelatin to foods. Bone marrow, a form of spongy tissue within some bones, contributes protein, fat and cholesterol. However, laboratory analysis has indicated that, in general, broths made only from bones provide little nutritional value and much of the protein in the bone does not dissolve.
According to the U.S. Department of Agriculture, bone marrow is safe to eat, assuming the meat from which it's derived is cooked to the appropriate internal temperature. Bone marrow from the spine of cows has been implicated in cases of bovine spongiform encephalopathy, or BSE, also known as mad cow disease; however, leg bones and oxtails of these animals are considered to be safe from BSE.
Despite a lack of research, bone broth recently has been promoted as a form of treatment for conditions ranging from autism to schizophrenia. There also has been a renewed interest in consuming bone broth due to the popularity of the Paleo diet. More research on contaminants in bone broth is needed.