Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. High Quality Content by WIKIPEDIA articles! An eating disorder is characterized by abnormal eating habits that may involve either insufficient or excessive food intake to the detriment of an individual's physical and emotional health. The causes of eating disorders are complex and not yet fully understood. Eating disorders are estimated to affect 5-10 million females and 1 million males in the United States. Although not yet classified as separate disorder, binge eating disorder is the most common eating disorder in the US affecting 3.5% of females and 2% of males according to a study by Harvard affiliated McLean Hospital. Bulimia nervosa was the second most common followed by anorexia nervosa.