Eating disorders have increased in frequency, possibly as a consequence of society's emphasis and preoccupation with thinness. Eating disorders are multifactorial conditions linked to genetic, traumatic, and nutritional causes. In North America, anorexia nervosa and bulimia nervosa are the two most common eating disorders. They predominantly affect women.
Anorexia nervosa is a psychiatric condition in which people intentionally starve themselves because of a false belief that they are fat, or for fear of becoming obese. In reality, they are almost always underweight or of normal weight when the condition starts. It is estimated that more than 90% of all those diagnosed with anorexia nervosa are women, often from middle and upper socioeconomic backgrounds. This disorder usually starts in the years between adolescence and young adulthood, with the average age at onset of 14 years. Anorexia nervosa afflicts about 1 in 100,000 people in the population at large, but the rate is believed to be higher among Caucasian adolescent girls, about 1 in 200.
Bulimia nervosa is an eating disorder characterized by uncontrolled or compulsive binge eating, usually followed by inappropriate ways of trying to get rid of the food. Most often, this involves purging by self-induced vomiting or abuse of laxatives, enemas, or diuretics. It's also sometimes called the "binge-purge syndrome." Some people with bulimia don't purge, but will overeat (consuming as many as 20,000 calories at one time) and then compensate for binge-eating sessions with other behaviors such as fasting or over-exercising. A person with bulimia may secretly binge anywhere from twice a week to several times a day. In most cases, binge eating is followed by purging. A person with bulimia may use as many as 20 or more laxatives at a time.
Bulimia commonly appears in the latter part of adolescence or early adulthood, but it can develop at an earlier or later age. Like anorexia, bulimia predominantly affects young, Caucasian, middle- and upper-class women. At some point in their lifetime, approximately 0.5% to 4% of women experience anorexia and between 1.0% and 4% experience bulimia.
Eating disorders are generally viewed as being psychological in origin. However, like depression, schizophrenia, and bipolar affective disorder, they are currently believed to have many causes - including genetic and functional changes in the brain. People suffering from anorexia and bulimia have preoccupations with body image, weight, and eating. They also have a distorted personal body image and a fear of fatness and weight gain.
Although cultural factors have an influence on the development of eating disorders, they appear to stem from multiple factors. There's been a lot of debate about the role of faulty parenting and dysfunctional family environments in relation to eating disorders. Genetic and hormonal factors are believed to play significant roles; people with eating disorders are believed to have a genetic predisposition to the illness. Individuals who have a family history of depression, alcohol abuse, obesity, or eating disorders are at higher risk for anorexia nervosa and bulimia nervosa. There also appears to be a neurologic relationship between eating behavior patterns (such as dieting and starvation) and the nervous and hormonal systems, since hunger, food cravings, and feelings of fullness are controlled by certain areas of the brain and involve a number of digestive hormones.