Sudden weight loss is a form of physical trauma that can result in thinning hair. This could happen even if the weight loss is ultimately good for you. It’s possible that the weight loss itself is stressing your body or that not eating right can result in vitamin or mineral deficiencies. Loss of hair along with noticeable weight loss may also be a sign of an eating disorder such as anorexia or bulimia.
What to do: "Sudden weight loss seems to shock the system and you’ll have a six-month period of hair loss and then it corrects itself,” says Dr. Hammonds.