Abstract: Alternatives described herein relate to methods for detecting, identifying, and/or diagnosing eating disorders, nutritional deficiencies, and/or malnutrition, including conditions such as bulimia nervosa and/or anorexia nervosa, by using X-ray diffraction on a sample of a tested subject's hair. In some alternatives, once an eating disorder, nutritional deficiency, or malnutrition is detected, identified, or diagnosed using the X-ray diffraction approaches set forth herein, a subject identified as having an eating disorder, nutritional deficiency, or malnutrition is provided counseling for the disorder and/or a medicament to treat, inhibit, or ameliorate said eating disorder or malnutrition, including Prozac, ami trip tyline, fluoxe tine, imipramine, Nardil, Tofranil, desipramine, Sarafem, Norpramin, and/or phenelzine.