Anorexia nervosa is a complex medical and psychological illness that cannot be defined by a single number on a scale. It often involves restrictive eating and/or weight loss, but the diagnosis is based on whether a child or adolescent is undernourished relative to their own personal growth trajectory, not simply whether they fall below an arbitrary BMI cutoff. As a result, some patients may meet criteria for anorexia even if their BMI appears “normal” or higher on standard charts. In younger patients, anorexia may also present not as obvious weight loss, but as an inability to gain weight and grow as expected over time. The illness may include fear of weight gain, preoccupation with shape or weight, and behaviors that interfere with adequate nourishment, whether overt or more subtle. At times, this may look like skipped meals, rigid food rules, or unnecessary dietary exclusions, even when a patient expresses a wish to get better. Many patients also struggle to fully appreciate the seriousness of their symptoms, despite concern from parents, coaches, or medical professionals. Left untreated, anorexia can become medically dangerous and deeply entrenched, which is why early, highly individualized, expert care is so important.
To be diagnosed with anorexia nervosa (AN) according to the DSM-5 TR, the following criteria must be met: 1
It is also important to recognize that a serious eating disorder may be present even when all formal DSM-5 criteria for anorexia nervosa are not fully met. In atypical anorexia nervosa, a patient may experience significant restriction, weight loss, and medical compromise without appearing underweight on a standard growth chart. Research has shown that the medical and psychological consequences of atypical anorexia can be every bit as significant as those of anorexia nervosa.
We believe families deserve to understand that anorexia nervosa is not simply an eating disorder — it is a serious, complex medical illness that can affect nearly every system in the body. As undernourishment progresses, the body begins to conserve energy in profound ways, often slowing essential functions in order to survive. Some of these changes improve with thoughtful nutritional rehabilitation and medical recovery, while others may have lasting consequences.
Heart and circulation
The cardiovascular system is often significantly affected. With ongoing malnutrition, the heart muscle may weaken and shrink, the heart rate may become dangerously slow, and blood pressure may fall. For some patients, this can lead to profound fatigue, weakness, lightheadedness, fainting, and in more severe cases, serious cardiac complications.
Digestive system
The digestive system commonly slows in response to starvation. This may present as constipation, bloating, nausea, abdominal discomfort, or feeling full after only a small amount of food. In more advanced illness, the body’s loss of protective fat stores can interfere with the normal function of the intestines and make eating physically uncomfortable.
Lungs and breathing
Although less often recognized, anorexia can affect the lungs as well. Severe malnutrition may increase the risk of aspiration, pneumonia, and other serious pulmonary complications, particularly as the body becomes more medically fragile.
Blood and bone marrow
Anorexia can suppress the bone marrow, where blood cells are produced. This may lead to anemia, low white blood cell counts, and low platelet counts, contributing to weakness, fatigue, and other signs that the body is no longer able to function as it should.
Hormones and reproductive health
When the body is not receiving adequate nourishment, hormone production is disrupted in order to conserve energy. In girls, menstrual periods often stop. In boys, testosterone levels may decline. Other hormone systems are also affected, reflecting the body’s attempt to prioritize survival over growth, development, and normal physiologic balance.
Muscles and bones
Loss of muscle mass is common and can become profound, leading to weakness, reduced stamina, and increased risk of falls. Bone health is also significantly affected. Children and adolescents with anorexia may experience early bone loss, placing them at risk for osteopenia, osteoporosis, and fractures. In some cases, this loss in bone density may not fully recover.
Brain and nervous system
Malnutrition affects the brain just as it affects the rest of the body. Severe anorexia can lead to changes in brain volume and may contribute to slowed thinking, difficulty concentrating, changes in temperature regulation, and other neurologic symptoms. While some of these changes improve with recovery, some effects may linger.
Skin, hair, and nails
Families may also notice outward signs of undernourishment, such as very dry skin, brittle hair and nails, bluish discoloration of the hands or feet, or the growth of fine soft hair on the body as the body attempts to preserve warmth. These physical changes are often visible markers of a much deeper medical illness.
Why early, specialized care matters
The most important message is that anorexia nervosa is a serious medical illness with real and potentially lasting consequences. It is not a phase, a lifestyle choice, or a matter of willpower. Early, highly specialized care can help restore medical stability, support healing, and protect a child or adolescent from complications that may become more difficult to reverse over time.
Citations:
1. American Psychiatric Association. (2022). Diagnostic and statistical manual of mental disorders: DSM-5-TR. American Psychiatric Association Publishing. https://doi.org/10.1176/appi.books.9780890425787
2. [6] Cost, J., Krantz, M. J., & Mehler, P. S. (2020). Medical complications of anorexia nervosa. Cleveland Clinic Journal of Medicine, 87(6), 361–366. https://doi.org/10.3949/ccjm.87a.19084
