Acute Anorexia Nervosa: The Most Severe Stage of Anorexia

Immune System

Acute anorexia nervosa (AN) is a severe psychiatric illness leading to serious health complications and, in some cases, death.

Unfortunately, treatment centers and hospitals are often ill-equipped to treat this advanced stage of anorexia, making it hard for many acute anorexia nervosa patients to find proper treatment.

What Is Acute Anorexia Nervosa?

Acute anorexia nervosa (AN) is anorexia in its most severe stage. Patients with acute anorexia nervosa have a BMI of less than 15 (i.e., less than 65% of their ideal body weight) and meet the DSM-5 diagnostic criteria for anorexia nervosa. [1]

Patients with acute anorexia nervosa can suffer from either the restricting subtype of anorexia (AN-R) or the binge-purge subtype (AN-BP). Restricting types lose weight by excessive fasting and dieting, while binge-purge types use compensatory behaviors like laxatives, diuretics, or vomiting to keep their body weight low.

Both types of AN may use obsessive exercise to burn calories and maintain low body weight.

Effects of Acute Anorexia Nervosa

Anorexia nervosa is a deadly eating disorder with a very high death rate compared to other mental illnesses. [2] The causes of death are widespread and can vary from person to person. Some people survive acute anorexia but struggle with related health problems for the rest of their lives.

Some of the body’s systems touched by extreme anorexia include:

  • The cardiovascular system
  • The immune system
  • The gastrointestinal system
  • Bone health
  • Mental health

Cardiovascular System 

Anorexia changes the shape and size of all muscles in the body, including the heart. And malnutrition can change the electrical systems the heart needs to beat properly.

People with extreme anorexia often have unusual heartbeat rates, and their hearts may push less blood with each beat. Both of these conditions can lead to sudden death. [3]

Immune System

Malnourished people often struggle with a poor immune system, and many people with anorexia battle with frequent colds, flus, and sore throats. But people with acute anorexia may have even more problems.

Researchers point out that many cells critical to the immune system develop inside the lymphatic system, including the bone marrow. People with anorexia don’t develop all of the cells they should, leaving them vulnerable to some types of infections. [4]

Gastrointestinal System 

People with anorexia often have the following issues: [5]

  • Esophageal pain
  • Stomachaches, especially in the early stages of recovery
  • Constipation

Stomach pain and constipation suggest food isn’t moving through the digestive tract properly, leading to a feeling of fullness and bloating.

Those symptoms could lead someone with acute anorexia to eat even less in an effort to find relief. That symptom could impede recovery.

Bone Health 

Low bone mass is common in people with anorexia, and the issue begins early on. [6] Malnutrition doesn’t provide your body with enough nutrients needed for bone health. Systems go awry, and the body breaks down bone without rebuilding depleted supplies.

Thin bones break easily. Some people with anorexia are diagnosed with the eating disorder when a slip or trip results in a catastrophic bone break. Others grow shorter each year as their spinal bones thin and collapse.

By the time anorexia reaches acute stages, a person’s skeletal system may be forever changed. Height lost can’t be regained, and broken bones may remain painful even after healing.

Mental Health 

While starvation from extreme anorexia causes significant health problems that can be fatal, the leading cause of death in anorexia is suicide. [2] People with anorexia often feel isolated, alone, and misunderstood.

As their illness deepens, so does their isolation. In time, suicide may seem like the only way out.


Refeeding Syndrome 

Another sometimes fatal complication of acute anorexia is called refeeding syndrome (RFS). Refeeding syndrome was first reported during World War II. Starved concentration camp occupants of Leningrad were liberated and began to eat again, only to mysteriously die a few days later.

This tragic phenomenon happened because their extreme electrolyte imbalances (thanks to malnutrition) caused their hearts to stop beating. Acute AN patients can die from RFS. [7]

Treatment for Acute AN

Chances for recovery greatly increase the earlier an eating disorder is detected and treated. [8] The sooner someone can get help, the better.

Since acute AN patients are often medically unstable, have severe health complications, and are extremely malnourished, treatment is typically conducted at a medical facility or medically-staffed treatment center.

Initial Tests

The first stages of acute AN treatment focus primarily on getting the patient medically stable and refer. The treatment team usually includes physicians, clinical psychologists, registered dietitians, and therapists. They run numerous tests (like blood tests, EKGs, blood pressure monitoring, and vital signs assessments) and develop a plan to get the patient stabilized and nutritionally rehabilitated.[1]

Unfortunately, many eating disorder treatment centers are not medically equipped to deal with acute AN patients, leaving severe AN cases for regular hospitals. The problem with this, however, is that most medical doctors and staff have not been specifically trained to treat eating disorders.

Importance of Seeking Eating Disorder Experts

Though hospital staff and doctors may be able to stabilize the patient and ward off an immediate threat of death, the patient’s underlying psychological problems are not dealt with and will often resurface and lead to another relapse.

This is why it’s so important to seek out a treatment center designed to treat eating disorders at every level, including acute anorexia nervosa.

Staffed with physicians, psychologists, dietitians, and therapists trained to treat eating disorders, these centers can address immediate health threats, stabilize the patient, and support long-term recovery and psychological healing.


  1. Gibson D, Watters A, Cost J, Mascolo M, Mehler PS. (2020). Extreme Anorexia Nervosa: Medical Findings, Outcomes, and Inferences from a Respective CohortJournal of Eating Disorders, 8(25).
  2. U.S. Department of Health and Human Services. (n.d.). Eating disorders. National Institute of Mental Health. Retrieved September 2022.
  3. Giovinazzo S, Sukkar SG, Rosa GM, Zappi A, Bezante GP, Balbi M, Brunelli C. (2019). Anorexia nervosa and heart disease: a systematic reviewEating and Weight Disorders, 24(2):199-207.
  4. Gibson D, Mehler PS. (2019). Anorexia Nervosa and the Immune System-A Narrative ReviewJournal of Clinical Medicine, 8(11).
  5. Santonicola A, Gagliardi M, Guarino MPL, Siniscalchi M, Ciacci C, Iovino P. (2019). Eating Disorders and Gastrointestinal DiseasesNutrients11(12):3038.
  6. National Institutes of Health. (2022). What People with Anorexia Nervosa Need to Know About Osteoporosis. National Institute of Arthritis and Musculoskeletal and Skin Diseases. Retrieved September 2022.
  7. Machado JD, Suen VM, Chueire FB, Marchini JF, Marchini JS. (2009). Refeeding syndrome, an undiagnosed and forgotten potentially fatal conditionBMJ Case Reports.
  8. National Eating Disorders Association. (2022). Warning Signs and Symptoms. National Eating Disorders Association. Retrieved September 2022.

The opinions and views of our guest contributors are shared to provide a broad perspective on eating disorders. These are not necessarily the views of Eating Disorder Hope, but an effort to offer a discussion of various issues by different concerned individuals.

We at Eating Disorder Hope understand that eating disorders result from a combination of environmental and genetic factors. If you or a loved one are suffering from an eating disorder, please know that there is hope for you, and seek immediate professional help.

Published October 10, 2022, on
Reviewed & Approved on October 10, 2022, by Jacquelyn Ekern MS, LPC