Energy expenditure during nutritional rehabilitation: a scoping review to investigate hypermetabolism in individuals with anorexia nervosa.

ABSTRACT

BACKGROUND: Weight gain and nutritional rehabilitation are essential first steps to achieve medical stabilization in anorexia nervosa, and frequent resistance to weight gain requires patients to consume high kilocalorie loads. Adaptive hypometabolism is common when patients begin treatment, and rebound hypermetabolism is suspected to be a significant barrier to weight gain. The aim of this review was to summarize existing data describing metabolic changes in anorexia nervosa during weight restoration. The reported findings challenge current hypotheses of weight gain resistance and highlight key areas for future research. METHODS: Using scoping review guidelines, three databases were searched for studies investigating metabolic changes in anorexia nervosa before and after renourishment. Two reviewers systematically screened the titles and abstracts of 447 articles, and full-text versions of 106 studies were assessed for eligibility. A total of 36 studies were included for review. Data regarding the study description, sample population (including age, weight, BMI, duration of treatment, and caloric intake), and metabolic variable descriptions were extracted. RESULTS: Female patients with anorexia nervosa from studies across 13 countries were included. Across the studies, average BMI increased from 13.7 kg/m2 at admission to 17.57 kg/m2. Patients presented to treatment with clinically reduced energy expenditure levels. After varying levels of nutritional rehabilitation and weight restoration, measured energy expenditure increased significantly in 76% of the studies. Energy expenditure values at the second timepoint increased to the standard range for normal weight female teenagers and adults. Despite these increases, the studies do not indicate the presence of a hypermetabolic state during renourishment. Additionally, all studies including both measured and predicted energy expenditure reported that predicted energy expenditure overestimated measured values. CONCLUSION: This study provides a detailed evaluation of the literature investigating energy expenditure and metabolic rate in patients with anorexia nervosa before and following a period of renourishment. The findings from this review identify important gaps in the current beliefs of energy expenditure in anorexia nervosa and highlight a need for further exploration of metabolic alterations during weight restoration.

Nutritional rehabilitation and weight restoration are two primary goals of anorexia nervosa treatment that pose significant physiological and psychological challenges for patients. Patients often require high caloric loads to continue an adequate weight gain trajectory, but the underlying cause of weight gain resistance remains unknown. We completed a scoping review of research into energy expenditure and metabolic rate during treatment. Our search identified 447 relevant articles from academic databases, and 106 were deemed eligible after screening. We extracted data, including sample characteristics, kilocalorie intake, energy expenditure, and treatment information, from 36 studies. When individuals arrived for treatment, their energy expenditure was lower than that of individuals without an eating disorder due to the prolonged state of nutrient deprivation. After varying amounts of time and kilocalorie intake, most studies reported significant increases in energy expenditure. However, energy expenditure after a period of renourishment did not indicate an overactive metabolism (i.e., "hypermetabolism"). Funders should consider supporting exploration of additional factors that may be functioning as barriers to weight gain during treatment, in pursuit of making treatment more efficient and long-lasting. Additionally, future research describing metabolism in anorexia nervosa should provide more consistent methodologies, robust statical testing, and comprehensive reporting of dietary intake.