Reduced Muscle Size and Physical Fitness in Anorexia Nervosa

Nutrition is one of the significant determinants of physical and psychological health. For this reason, refeeding, weight restoration, and recovery of a healthy nutritional status are key effective elements in treating anorexia nervosa.

Proteins, in particular, play a crucial role in regulating metabolic health and longevity, and recent studies found that muscle size and strength predict quality of life and mortality. However, the clinicians involved in managing eating disorders have mainly ignored the restoration of muscle size and function.

A recent systematic review of 30 studies published in the International Journal of Eating Disorders has summarized the current knowledge about muscle size and function in people with anorexia nervosa before and after weight restoration. In this post, I describe the main finding of the review with some adjunctive data derived from a study by my team, and I will discuss the clinical considerations and future research on this topic.

Muscle mass/lean mass before and after weight restoration

The review of the 11 studies (404 participants) that have measured muscle mass, lean mass, or muscle in underweight people with anorexia nervosa found that those with anorexia nervosa, in comparison to controls, have a mean reduced muscle size of 24 percent.

Eleven studies (403 participants) have also assessed muscle mass/lean mass after weight restoration in people with anorexia nervosa. Compared with healthy controls, weight-restored people with anorexia nervosa have a mean reduced muscle size of 9.1 percent with respect to healthy controls.

One study, which assessed measured muscle size after an average of 27 years of follow-up, found that people with a history of anorexia nervosa have a 12 percent lower muscle mass compared to age-matched healthy controls.

Physical fitness before and after weight restoration

Physical fitness is defined as a state of well-being with a low risk of premature health problems and the energy to participate in a variety of physical activities or capacities.

Four studies (50 participants) assessed the muscular strength of people with anorexia nervosa before weight restoration. On average, those with anorexia nervosa have an average of 35.2 percent lower muscle strength than healthy controls. To better understand the physical impairment associated with this muscle deficit, it has been estimated that young adult women with anorexia nervosa have a grip strength comparable to that of 70- to 79-year-old women.

One study (20 participants) evaluated muscle strength in people with anorexia nervosa after weight restoration at 27 years of follow-up. The study found that they had 27 percent lower muscle strength than healthy controls.

A study by my team evaluated the physical fitness of 37 people with anorexia nervosa before and after weight restoration with a residential enhanced cognitive behavioral therapy. Physical fitness was assessed with the Eurofit Physical Fitness Battery. The study found that people with anorexia nervosa have lower muscular strength than controls and a deterioration in cardiorespiratory resistance, flexibility, and balance. The fitness measures improved significantly with weight restoration but remained significantly lower than those assessed in controls.

Implications for the treatment of anorexia nervosa and future research

The incomplete restoration of muscle mass and improvement in physical fitness after weight restoration indicate that nutritional rehabilitation and weight regain are insufficient per se to produce a complete restoration of physical fitness in people with anorexia nervosa.

Data from participants in the Minnesota Starvation Experiment found that the rehabilitation period was considered the most challenging part of the experiment and that the feeling of tiredness and weakness was very slow to improve. They reported not being back to normal by the end of the three-month recovery period and estimated that the time to achieve a full recovery ranged from two months to two years. It is possible, also for patients with anorexia nervosa, that a normal body composition and fitness restoration requires a long period of weight maintenance after the weight regain phase. However, two strategies are under study to improve a more rapid restoration of muscle size and function in people with anorexia nervosa.

The first strategy is integrating the available treatments with individualized health-enhancing physical activity programs during the weight restoration phase. A healthy program of physical activity, in patients with stable medical conditions, has the potential to improve the quality of life and well-being of people with anorexia nervosa by improving physical health and by alleviating psychological and social disability. Adequate physical activity programs might also enhance the treatment of eating disorders, both because there is evidence that physical activity positively affects the treatment of depression and anxiety, two common comorbid conditions of eating disorders, and because physical activity might improve the poor physical fitness of people with anorexia nervosa.

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In addition, the inclusion of healthy exercising might improve patients’ sense of well-being and, if implemented in the form of social exercising, as suggested by some clinical guidelines, might help patients to escape from isolation, practice body exposure, facilitate the acceptance of the changes in their shape and weight, and discharge the urge to exercise, a common problem observed in people with an eating disorder,

The second strategy currently evaluated in a double-blind placebo-controlled trial is dietary supplementation with a blend of essential amino acids (containing a high percentage of branched-chain amino acids (leucine, isoleucine, valine) during the weight restoration of patients with anorexia nervosa. Previous studies have found that chronic food supplementation of essential amino acids containing a high percentage of branched-chain amino acids preserves mitochondrial metabolism and greater physical resistance in elderly mice, increasing their survival. Moreover, amino acid mixtures also seem to counteract the functional atrophy of skeletal muscles in elderly and cachectic or sarcopenic individuals and improve cognitive functions.

The study will evaluate if people with anorexia nervosa receiving the supplementation compared to those who receive placebo will achieve a higher percentage increase in muscle mass, a more significant improvement in physical fitness, and a more significant reduction in eating disorder psychopathology and psychosocial impairment secondary to the eating disorder.