Anorexia and hypermetabolism

What is hypermetabolism? 

Hypermetabolism is a condition describing an increase in the body's basal metabolic rate (BMR), or the amount of calories required to perform basic, life-sustaining functions when the body is at rest. In other words, the BMR represents the minimum number of calories the body burns simply by existing.

When someone reaches a point of hypermetabolism, their BMR increases and their body starts burning higher amounts of calories, including while at rest. This often leads to weight loss, even with increased energy intake. 

Causes of hypermetabolism

Hypermetabolism or hypermetabolic conditions can occur in many different scenarios, particularly when the body needs to produce more energy than normal to heal itself.

For example, if someone has suffered severe burns, multiple fractures, infection or sepsis, traumatic brain injury, or undergone surgery, their body will become hypermetabolic, increasing energy output in order to facilitate the healing process.^1,2,3,4

It's also possible for hypermetabolism to develop from other causes, including hyperthyroidism, a condition in which the thyroid produces too many hormones, ultimately speeding up the body's internal processes and kicking metabolism into overdrive.⁷

Hypermetabolism symptoms

Hypermetabolism may be useful in short stints, such as helping someone produce enough energy to facilitate healing, but if it occurs long-term, it can become a serious medical condition.

Some studies have shown that the increase of catabolic activity—or the breakdown of food into more usable components like carbohydrates, protein, and fat—can increase insulin resistance. This, in turn, can result in higher blood sugar levels, which, in itself, can bring on a number of other health complications.⁸

Other symptoms of hypermetabolism include:⁵

• Anemia
• Elevated or irregular heart rate
• Increased body temperature
• Shortness of breath
• Muscle weakness and fatigue
• Heat sensitivity
• Excessive sweating

Hypermetabolism and anorexia 

When it comes to anorexia nervosa, hypermetabolism isn't a symptom of the condition, but rather a potential complication of recovery.

The disordered eating patterns generally associated with AN often lead to starvation or severe malnutrition, causing the body to break down fat and muscle in order to supply energy to sustain life. This has its own effect on the metabolic rate, generally working to slow the process down as the body adjusts to receiving less energy.

For people with AN and other restrictive eating disorders, the danger of becoming hypermetabolic sets in during the nutritional rehabilitation phase.⁶ When the body is used to receiving so little, the reintroduction of even a small amount of outside energy can kick the metabolic rate into high gear, as the body eagerly works to break down and absorb these additional resources.

Some studies have shown that people who struggle with AN remain hypermetabolic well into recovery, requiring even more calories than normal to maintain weight restoration long-term.⁶ They may also continue to lose weight easily or have trouble with weight gain, as the body continues to adjust to new food intake levels.⁶

Hypermetabolism and eating disorder recovery

Indeed, the refeeding process is often considered one of the most dangerous parts of AN recovery, especially early on. Medical supervision during this stage is very important.

In extreme cases of prolonged starvation, the body becomes depleted of many nutrients, fats, and proteins. If food is reintroduced too quickly, the hypermetabolism set off by this change can lead to rapid and dangerous changes and chemical reactions, including potentially deadly electrolyte imbalances and cardiac arrhythmias.¹⁰

Scientists are generally split on the proper pace to reintroduce calories to someone's diet, and much of the process depends deeply on details of individual cases. But in every case, it's important to work with a team of professionals to help restore weight in a safe and healthy way.

Finding help for anorexia nervosa

If you or a loved one are struggling with anorexia nervosa or another eating disorder and have lost significant body weight, it's important to seek out the appropriate type of treatment and care.

Your primary care physician, therapist, psychiatrist, or another trusted medical professional can help, giving you an official diagnosis, pointing you in the direction of a successful treatment program, or otherwise helping you plan the next best steps.