Anorexia nervosa is defined by three core characteristics: restricted eating that leads to significantly low body weight, an intense fear of gaining weight, and a distorted perception of one’s own body size or shape. It affects up to 3% of young women and carries the highest mortality rate of any psychiatric disorder, with roughly 5% of patients dying within four years of diagnosis. But the disorder’s characteristics extend well beyond what shows up on a scale. It reshapes how a person thinks, how their body functions, and how they move through daily life.
The Three Diagnostic Criteria
A diagnosis of anorexia nervosa requires all three of the following. First, the person restricts their food intake enough to maintain a body weight significantly below what’s expected for their age, sex, and overall health. Second, they experience an intense fear of gaining weight or consistently behave in ways that prevent weight gain, even when they’re already underweight. Third, they have a distorted relationship with their own body, whether that means seeing themselves as larger than they are, tying their self-worth almost entirely to their weight or shape, or simply not recognizing how serious their low weight has become.
Severity is classified by BMI. Mild anorexia corresponds to a BMI of 17 or above, moderate falls between 16 and 16.99, severe between 15 and 15.99, and extreme is anything below 15. In one clinical sample, nearly 29% of patients fell into the extreme category at the time of evaluation.
Restricting Type vs. Binge-Purge Type
Anorexia nervosa has two recognized subtypes, and they look quite different in practice. The restricting type involves weight loss through dieting, fasting, or excessive exercise without regular episodes of binge eating or purging. The binge-eating/purging type involves cycles of eating larger amounts of food followed by self-induced vomiting, laxative use, or other compensatory behaviors, all while still maintaining a dangerously low weight.
In clinical studies, the split is roughly even: about 55% restricting type and 45% binge-purge type. People with the binge-purge subtype tend to score higher on measures of dietary restraint, eating concern, and preoccupation with shape and weight. Despite those differences in severity of psychological symptoms, both subtypes cause comparable levels of real-world impairment in work, relationships, and daily functioning.
Psychological Characteristics
Anorexia isn’t just about food. The psychological profile is remarkably consistent across patients and includes several traits that often predate the eating disorder itself. Perfectionism, rigidity, and obsessive tendencies are hallmarks. People with anorexia score significantly higher than the general population on measures of maladaptive perfectionism, emotional overcontrol, difficulty with change, and reluctance to delegate tasks to others.
Cognitive inflexibility is one of the most studied features. This means difficulty shifting between tasks or perspectives, a tendency toward black-and-white thinking, and rigid rules around food, routines, and self-evaluation. Importantly, this inflexibility often persists even after weight is restored, suggesting it’s a trait woven into the person’s thinking style rather than just a symptom of starvation. Research has found that obsessive-compulsive traits in childhood increase the risk of developing an eating disorder later, and that perfectionism specifically predicts a poorer prognosis over time.
Behavioral Warning Signs
The observable behaviors of anorexia extend beyond simply eating less. People with the disorder often develop elaborate rituals around food: cutting it into tiny pieces, rearranging it on the plate, eating in a specific order, or taking unusually long to finish a meal. They may avoid eating in social settings entirely, making excuses to skip meals with family or friends.
Excessive exercise is another common feature. This can look like rigid workout routines that continue regardless of illness, injury, or exhaustion, often driven by the need to “earn” food or counteract calories consumed. The exercise itself may seem healthy to outside observers, which makes it easy to miss as a warning sign. Other behavioral patterns include wearing loose or layered clothing to hide weight loss, obsessive calorie counting, and a growing preoccupation with cooking for others while refusing to eat the food themselves.
Physical Signs and Medical Complications
The body adapts to prolonged starvation in ways that are visible and measurable. One of the most recognizable physical signs is lanugo, a layer of fine, downy hair that grows on the face and arms as the body tries to insulate itself against heat loss. Brittle nails, thinning scalp hair, and a yellowish tint to the skin (from elevated levels of a pigment found in vegetables) are also common.
Cardiovascular changes are among the most dangerous. A slow heart rate, called bradycardia, is the most common heart-related finding. Rates as low as 25 beats per minute have been documented. Low blood pressure frequently accompanies this. The heart’s electrical system can also be affected, with changes in the heart’s rhythm timing that increase the risk of dangerous arrhythmias. Paradoxically, if a person with severe anorexia develops a heart rate in the 80 to 90 range, something that would be normal in a healthy person, it can signal a serious secondary illness.
Blood work often looks deceptively normal, even in severe cases. The body is remarkably good at maintaining electrolyte balance during starvation. When abnormalities do appear, they include low blood cell counts (anemia, low white blood cells, low platelets), low sex hormones, and vitamin D deficiency. Electrolyte disturbances like low potassium and low sodium are more typical in the binge-purge subtype due to fluid losses from vomiting or laxative use.
Bone loss is a frequent and serious consequence. Both adolescents and adults with anorexia develop weakened bones at rates far higher than the general population, leading to increased fracture risk that can persist long after recovery.
Who It Affects
The median age of onset is 18, though it can begin earlier in adolescence or later in adulthood. Anorexia is about three times more common in women than men, with lifetime prevalence rates of 0.9% in females and 0.3% in males. Among adolescents aged 13 to 18, eating disorders overall are more than twice as prevalent in girls (3.8%) compared to boys (1.5%). That said, anorexia in men and boys is underdiagnosed, partly because screening tools and clinical awareness have historically been oriented toward women.
Atypical Anorexia Nervosa
Not everyone with anorexia is visibly underweight. Atypical anorexia nervosa involves the same fear of weight gain, the same body image disturbance, and significant weight loss, but the person’s current weight falls within or above the normal range. This can happen when someone starts at a higher weight and loses a substantial amount rapidly. At least 25% of adults diagnosed with atypical anorexia are currently overweight or obese, a figure that rises to 40% among men with the condition.
The medical and psychological consequences of atypical anorexia are comparable to those of the standard diagnosis. The danger is that because these individuals don’t “look” anorexic, they’re less likely to be identified by family, friends, or even healthcare providers. The defining characteristics, the restrictive eating, the fear, the distorted body image, are identical. Only the number on the scale differs.