Though the chocolate flavoring is often an enticement, it is unsound from a nutritional standpoint. The oxalic acid in chocolate inhibits the digestive system's ability to absorb the calcium in chocolate milk. The oxalic acid chemically reacts with the calcium, producing a new compound, calcium oxalate. The intestines cannot absorb this calcium oxalate because it is insoluble. This loss of the essential mineral calcium is nutritionally detrimental, especially for growing children.
** Asian Recipes