The American Journal of Clinical Nutrition published a study of two adult hospital patients who were unable to use their intestines to digest food. The patients were fed intravenously a diet that happened to be deficient in the B-complex vitamin biotin. Biotin deficiency is extremely rare because in addition to being present in many types of food, it is also manufactured by the friendly bacteria that live in normal intestines. Because these patients had inactive intestines, their intestinal bacteria did not produce adequate biotin, and they suffered hair loss as a result. When biotin was added to the intravenous diet, hair growth resumed.