When people with eating disorders are hospitalized and need to rebuild their health, doctors need to know exactly how many calories their bodies need. This review looked at 19 studies involving 624 patients to see how well a special test called indirect calorimetry works for measuring calorie needs in these patients. The test measures how much oxygen your body uses to figure out how many calories you burn. While this test is considered the best way to measure calorie needs, doctors don’t have much guidance on when and how to use it safely in eating disorder patients who are being refed. The research shows the test is safe, but more studies are needed to figure out the best way to use it.

The Quick Take

  • What they studied: How well a special breathing test (indirect calorimetry) works to measure how many calories people with eating disorders need when they’re in the hospital getting better
  • Who participated: 624 patients across 19 different studies, all diagnosed with anorexia nervosa, all hospitalized and very underweight (BMI between 9.6-15.4)
  • Key finding: The breathing test is safe to use in hospitalized eating disorder patients, but doctors don’t yet know the best time during recovery to use it, or how to use it most effectively
  • What it means for you: If you or someone you know is hospitalized for an eating disorder, this test may be used to help figure out the right amount of food needed for recovery. It’s safe, but doctors are still learning the best way to use it. Talk to your medical team about whether it’s right for your situation.

The Research Details

This was a scoping review, which means researchers looked at all the published studies they could find on a topic and summarized what they learned. The team searched four major medical databases for studies published anytime up to April 2024 that described using indirect calorimetry (a breathing test) in hospitalized adults with eating disorders who were being refed. Two researchers independently reviewed each study to make sure it met the requirements. They looked at 641 articles total and found 19 that actually studied this topic.

Indirect calorimetry works by measuring how much oxygen your body uses and how much carbon dioxide you produce when you breathe. From these measurements, doctors can calculate exactly how many calories your body is burning. This is considered the most accurate way to measure calorie needs, which is why it’s called the ‘gold standard’ method.

The researchers collected information about each study’s design, the patients involved, what eating disorder they had, what food plan they were given, and details about how the breathing test was performed.

For people with eating disorders being hospitalized, getting the right amount of calories during recovery is extremely important—too little and they won’t heal properly, too much too fast can cause serious medical problems. Having an accurate way to measure calorie needs could help doctors create safer, more personalized recovery plans. However, people with eating disorders are very fragile medically, so doctors need to know that any test they use is safe and actually helpful.

This review is reliable because two independent researchers reviewed each study to reduce bias, and they searched multiple major medical databases. However, the review found that most of the original studies were small and didn’t report important details about patients’ mental health conditions or practical challenges of using the test. The fact that only 19 studies met the criteria shows this is an understudied area, which means there’s still a lot we don’t know.

What the Results Show

The review found 19 studies involving 624 patients, all with anorexia nervosa (the most severe type of eating disorder), all hospitalized due to serious medical complications from being severely underweight. All patients had a BMI (a measure of weight relative to height) between 9.6 and 15.4, which is dangerously low.

The breathing test (indirect calorimetry) was performed safely in all these patients. Before the test, patients fasted (didn’t eat) for at least 10-12 hours, and no serious problems were reported from this fasting period. This is important because these patients are medically fragile, so knowing the test doesn’t cause harm is valuable.

However, the studies showed very different approaches to when the breathing test was done during the recovery process. Some did it early in hospitalization, others later, and there was no clear pattern. This means doctors don’t yet know the best time to perform the test to help guide feeding decisions.

The studies also didn’t provide much information about patients’ mental health conditions (like depression or anxiety) that often go along with eating disorders, or practical tips for using the test safely in this vulnerable population.

The review found that while the breathing test itself is safe and feasible to use in hospitalized eating disorder patients, there’s very little guidance on how to actually use the results to plan meals. The studies didn’t clearly explain whether knowing the exact calorie needs from the test actually led to better patient outcomes or safer recovery. Additionally, most studies didn’t discuss how to handle the emotional or psychological aspects of the test, which could be important for patients with eating disorders who may have anxiety around food and body measurements.

This is the first comprehensive review of how the breathing test is used specifically in hospitalized eating disorder patients. Previous research has shown the test works well in other patient populations, but eating disorder patients are unique because they’re medically unstable and psychologically vulnerable. This review shows that while the test appears safe in this group, we need much more research to understand if it’s actually helpful compared to other ways of calculating calorie needs.

The main limitation is that only 19 studies were found, and they were all quite small and varied in how they did things. All patients studied had anorexia nervosa, so we don’t know if the results apply to other eating disorders like bulimia or binge eating disorder. The studies didn’t report much information about patients’ mental health conditions or how the test affected their psychological wellbeing. Most importantly, none of the studies clearly showed whether using this test actually led to better recovery outcomes compared to other methods of calculating calorie needs.

The Bottom Line

Based on this review, indirect calorimetry appears to be a safe tool that can be used in hospitalized eating disorder patients (moderate confidence). However, there isn’t yet strong evidence that it should be routinely used or that it leads to better outcomes (low confidence). If your medical team suggests using this test, it’s safe to proceed, but ask them how they’ll use the results to guide your nutrition plan. More research is needed before clear guidelines can be made.

This research is most relevant to doctors, nutritionists, and hospitals that treat hospitalized eating disorder patients. If you’re being treated for an eating disorder in a hospital, this information helps explain what the breathing test is and that it’s safe. Family members of people with eating disorders may find it helpful to understand the tools doctors use. This research is NOT meant to guide self-treatment or outpatient eating disorder management.

If the breathing test is used, results are available immediately (within hours). However, seeing benefits from using this test to guide nutrition would take weeks to months, as recovery from eating disorders is a gradual process. Don’t expect dramatic changes right after the test—it’s one tool among many in a comprehensive treatment plan.

Want to Apply This Research?

  • If hospitalized for an eating disorder treatment, track the dates when indirect calorimetry tests are performed and note your calorie intake goals before and after the test. Record any changes your medical team makes to your nutrition plan following the test results.
  • Work with your medical team to understand your personalized calorie needs based on test results. Use the app to log meals according to the nutrition plan created from your test results, and track how you feel physically and emotionally as you follow this plan.
  • Monitor trends in your energy levels, physical symptoms, and medical stability over weeks and months as you follow a nutrition plan informed by the breathing test. Share this data with your treatment team to help them assess whether the test-guided approach is working for your recovery.

This research summary is for educational purposes only and should not replace professional medical advice. Indirect calorimetry and nutrition planning for eating disorders should only be performed under the supervision of qualified healthcare professionals in appropriate medical settings. If you or someone you know is struggling with an eating disorder, please seek help from a doctor, registered dietitian, or mental health professional. In crisis situations, contact the National Eating Disorders Association (NEDA) Helpline at 1-800-931-2237 or the Crisis Text Line by texting ‘NEDA’ to 741741.