HBC205: Human Biochemistry - Anorexia Nervosa Metabolic Adaptations

This assignment explores the metabolic adaptations that occur in individuals with Anorexia Nervosa, an eating disorder characterized by severe energy restriction and a fear of weight gain. The body responds to the inadequate energy intake through a series of hormonal and metabolic adjustments. Initially, glycogen stores are mobilized, followed by gluconeogenesis and the breakdown of triacylglycerols for energy. Prolonged starvation leads to the utilization of ketone bodies by the brain, heart, and kidneys to spare glucose for critical tissues like erythrocytes and the adrenal medulla. The assignment highlights the homeostatic mechanisms that aim to maintain blood glucose levels and conserve proteins during the state of starvation. The provided solution includes relevant references to support the findings.

ANOREXIA NERVOSA: metabolic adaptations
Introduction
Anorexia Nervosa is an eating disorder that is characterized by reduced body weight due
to inadequate energy intake and a great fear of weight gain. Individuals may control
weight gain through excessive exercise, restricted food intake or expulsion of food by
vomiting or use of laxatives. Symptoms of the disorder are indicative of starvation and
include fatigue, dizziness, sleeping problems, low blood pressure, electrolyte imbalance
and osteoporosis.( Fazeli and Klibanski,2018)
The body adapts to the inadequate energy supply through various hormonal and metabolic
processes. Insulin, estrogen, testosterone, leptin, T3 (Triiodothyronine) levels reduce.
Cortisol, glucagon, epinephrine, norepinephrine, insulin like growth factor -1, ghrelin and
β-endorphin on the other hand rise.( Méquinion et al., 2013). Energy is conserved while
reproduction and growth are inhibited. The basal metabolic rate is also reduced.( Müller et
al, 2015) Initial lack of food results in mobilization of glycogen stores. Glycogen
phosphorylase is activated via phosphorylation through a cyclic AMP cascade. However,
these reserves are depleted in a day. Gluconeogenesis in the liver then occurs and glucose
is transported to other organs. Triacylglycerols are broken down yielding fatty acid and
glycerol. The liver energy needs are met by oxidation of fatty acids. Muscles eventually
utilize fatty acids from the adipose tissue. Prolonged starvation shifts the brains, heart and
kidney energy source into ketone bodies. The shift from glucose to ketone bodies allows
the body to spare glucose for erythrocytes and the adrenal medulla. The Muscle protein is
also maintained with only marked utilization in the initial stages of starvation.(Berg et
al.,2015
Conclusion
There is homeostatic control even in Anorexia Nervosa. The blood glucose levels are kept
at a constant and body functions maintained through conserving proteins.
References
Berg, J. M., Tymoczko, J. L., Gregory J. Gatto, J., & Stryer, L. (2015). Biochemistry. W.
H. Freeman.
Fazeli, P. K., & Klibanski, A. (2018). Effects of anorexia nervosa on bone metabolism.
Endocrine Reviews, 39(6), 895-910.
Müller, M. J., Enderle, J., Pourhassan, M., Braun, W., Eggeling, B., Lagerpusch, M., …
Glüer, C. (2015). Metabolic adaptation to caloric restriction and subsequent refeeding:
The Minnesota starvation experiment revisited. The American Journal of Clinical
Nutrition, 102(4), 807-819.
Méquinion, M., Langlet, F., Zgheib, S., Dickson, S., Dehouck, B., Chauveau, C., &
Viltart, O. (2013). Ghrelin: Central and peripheral implications in anorexia nervosa.
Frontiers in Endocrinology, 4.