Anorexia nervosa, often referred to simply as anorexia, is an eating disorder characterized by low weight, fear of gaining weight, and a strong desire to be thin, resulting in food restriction. Many people with anorexia see themselves as overweight even though they are in fact underweight. If asked they usually deny they have a problem with low weight. Often they weigh themselves frequently, eat only small amounts, and only eat certain foods. Some will exercise excessively, force themselves to vomit, or use laxatives to produce weight loss. Complications may include osteoporosis, infertility and heart damage, among others. Women will often stop having menstrual periods.