Might Starvation-Induced Adaptations in Muscle Mass, Muscle Morphology and Muscle Function Contribute to the Increased Urge for Movement and to Spontaneous Physical Activity in Anorexia Nervosa?

Regina C Casper

doi:10.3390/nu12072060

Abstract

Severely undernourished and underweight anorexia nervosa (AN) patients typically remain active and mobile. Might such persistent physical activity in AN be supported by specific adaptations in muscle tissue during long term undernutrition? To identify potential differences, studies examining the effects of undernutrition on skeletal muscle mass, muscle morphology and muscle function in healthy humans and in AN patients were reviewed. Adjustments in muscle morphology and function in AN did not differ in substance from those in healthy humans, undernourished people, or undergoing semi-starvation. Loss of muscle mass, changes in muscle contractility and atrophy of muscle fibers (predominantly type II fibers) characterized both groups. Muscle innervation was unaffected. Work capacity in men in semi-starvation experiments and in females with AN declined by about 70% and 50%, respectively. Perceptions of fatigue and effort distinguished the groups: signs of general weakness, tiring quickly and avoidance of physical activity that were recorded in semi-starvation were not reported for AN patients. The absence of distinctive starvation-related adjustments in skeletal muscle in AN suggests that new methods, such as muscle gene expression profiles in response to deficient nutrient intake, and better knowledge of the central regulatory circuitries contributing to motor urgency will be required to shed light on the persistent mobility in AN patients.

Highlights

Anorexia nervosa (AN), a disorder principally of female adolescents, is characterized by prolonged self-imposed restriction of food intake leading to significant weight loss and an emaciated appearance, the result of loss of fat tissue and of muscle tissue
Under fasting conditions, following significant restriction of food intake, a low blood sugar level leads to decreased secretion of insulin and increased secretion of glucagon [14]
With glucose levels insufficient to provide glucose to the brain and other tissues, after several weeks of starvation, ketone bodies become the major fuel for the brain

Summary

Introduction

Anorexia nervosa (AN), a disorder principally of female adolescents, is characterized by prolonged self-imposed restriction of food intake leading to significant weight loss and an emaciated appearance, the result of loss of fat tissue and of muscle tissue. The body responds to the caloric restriction with adaptive metabolic and physiological responses not different from those found in starvation [1]. Many adjustments, such as hypothermia, hypotension, bradycardia, and a low resting metabolic rate, are aimed at preserving energy [2]. The apparent ease with which previously healthy teenagers lose up to 40% of their body weight poses the question whether other factors besides a restricted caloric intake might facilitate weight loss in AN. In Lasègue’s words: “another ascertained fact is, Nutrients 2020, 12, 2060; doi:10.3390/nu12072060 www.mdpi.com/journal/nutrients

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