The quantity and quality of the hair are closely related to the nutritional state of an individual. And yet, there is hardly another field with so much prejudice, misconception, and debate as diet and health, let alone hair health. Pharmacy aisles and Internet drugstores are full of nutritional supplements promising full, thick, luscious hair for prices that range from suspiciously cheap to dishearteningly exorbitant. Since there lies an important commercial interest in the nutritional value of various nutritional supplements, a central question that arises is whether...