Alterations in the Resting Metabolic Rates of Patients Suffering from Anorexia Nervosa and Bulimia Nervosa
- Decreased lean body mass results in reduced metabolism.
- Starvation stimulates a decrease in the production of the hormone leptin.
- Leptin determines energy expenditure.
- Purging or self-induced vomiting affects resting glucose levels and leptin levels.
- Metabolic rate increases exponentially during weight restoration in anorexia.
- Binge-eating and purging decreases metabolic rate for months or even years.
- Restoration of normal metabolism is contingent upon normalized eating patterns.
The Basics of Metabolism:
How Metabolic Rate is Determined:
Resting metabolism rate is determined by body mass, primarily fat-free mass (FFM) or lean body tissue, and when an anorectic patient begins restricting, he or she begins to lose adipose tissue and muscle, results in a decrease of resting energy rate (REE) [1,3,4]. In other words, as the person begins to lose body mass, he or she requires less energy in the form of calories in order to maintain his or her current weight. Conversely, when he or she begins the weight restoration process and begins to gain back the fat and muscle that were lose, his or her caloric needs increase as body mass increases .
The Effect of Starvation on Metabolism:
Even a significant decrease in body weight does not explain the drastic reduction of resting metabolic rate as is seen in patients with anorexia nervosa [2,4]. Polito et. al (2000) found that leptin, an important hormone that regulates energy expenditure, was found to be 76% lower in anorexia patient than in healthy controls. Additionally, several studies have found that the resting metabolic rate of patients with anorexia had decreased to be between 25% to 70% of the expected rate [1,3,4]. In other words, although decreased body mass leads to a lower resting metabolic rate, the significantly decreased metabolic rate as seen in anorexia patients is also the result of altered hormone levels, as an adaptation to energy conservation during starvation.
The Effect of Weight Restoration on Metabolism:
Strangely, many patients experienced a drastic increase in metabolic rate at some period during the weight restoration process, much to the consternation of dietitians and attending doctors, as well as the patient themselves. How frustrating for the patient to be eating appropriately for the first time in what may be years and to be betrayed by the body by losing more weight! While one study conducted in the 1980’s by Kaye et al. (1986) found that recently weight-restored anorectics had a higher activity level than healthy controls, most studies attribute the sudden increase in metabolic rate to an increase in leptin, which as discussed earlier, is thought to be responsible for determining metabolic rate in states of starvation [6,7].
Metabolic rate increases with weight:
The Effect of Binge/Purge Cycles on Metabolism:
Considering the complexity and remaining mysteries of the effect of starvation on metabolisms in patients with anorexia, one can only imagine the complexities of determining the effect on metabolism of a cycle of restricting, binge eating, and purging that is seen in patients with bulimia. Although weight does not always decrease in bulimic patients, which would account for a decrease in resting metabolism, several studies still show a significant decrease in metabolic rate in patients who regularly binge and purge that is likely attributed to a decrease in leptin [4,8,9]. Furthermore, one study showed similar results in patients who engaged in a binge-restrict cycle that resulted in an increase in adipose tissue and a decrease in lean body weight, possibly to protect from the anticipated period of famine .
Long-term Effects of Eating Disorders on Metabolism:
Fortunately, metabolic rate seems to normalize along with eating patterns and the completion of the weight restoration process in patients with anorexia, whereas the metabolic rate seen in bulimic patients seems to be normalized more slowly, with complete normalization seen over the course of several months or even years, with the contingency that normal eating patterns and healthy body weight are maintained [5,8]. Consequently, the restoration of normal metabolic rate is possible but requires the patient to maintain a dedication to normalizing eating patterns and stabilizing at a healthy, normal weight.
Binge-ing and Purging Marathons: Repeated Binge/Purge Cycles in Bulimia Nervosa (via Tetyana at Science of EDs)
Hypermetabolism in Anorexia Nervosa (via Tetyana at Science of EDs)
More on Hypermetabolism (Carrie Arnold via ED Bites)
 Weisman C. and Hashem R. ”Starvation.” Surgical Metabolism: The Metabolic Care of the Surgical Patient. Davis K. A. and Rosenbaum S. H., eds. New Haven, CT: Springer Science, 2014. 71 - 88.
 Polito et al. 2000. Basal metabolic rate in anorexia nervosa: relation to body composition and leptin concentrations. American Journal of Clinical Nutrition 71(6): 1495 - 1502.
 Kosmiki et al. 2013. Chronic starvation secondary to anorexia nervosa is associated with an adaptive suppression of resting metabolic rate. The Journal of Clinical Endocrinology and Metabolism 99(3): pages unknown.
 Black et al.. ”Alterations in Metabolism and Energy Expenditure in Eating Disorders.” Medical Issues and the Eating Disorders: The Interface. Kaplan A. S. and Garfinkel P. E., eds. New York, NY: Routledge, 2013.
 Kaye et al. 1986. Caloric consumption and activity levels after weight recovery in anorexia nervosa: a prolonged delay in normalization. International Journal of Eating Disorders 5(3): 489 - 502.
 Hebebrand et al. 2007. The role of leptin in anorexia nervosa: clinical implications. Molecular Psychiatry 12: 23 - 35.
 Hebebrand et al. 1997. Leptin levels in patients with anorexia nervosa are reduced in the acute phase of the illness and elevated upon short-term weight restoration. Molecular Psychiatry 2(4): 330 - 334.
 Obarzanek et al. 1991. Reduced resting metabolic rate of patients with bulimia nervosa. Archives of General Psychology 48(5): 456 - 462.
 Taylor et al. 1998. Impact of binge eating on metabolic and leptin dynamics in normal young women. The Journal of Clinical Endocrinology and Metabolism 84(2): 428 - 434.