Question

A 26-year-old male prisoner begins a hunger strike to protest what he considers unfair prison policies. He drinks only tap water, and his only exercise is two daily half-hour walks at approximately 2.5 miles/hr. The temperature in his cell is maintained at 220C. His starting weight is 70 Kg, of which 14% is body fat. At the end of 4 weeks, he is urged by the prison physician, family, friends, and his attorney to stop his fast because of his deteriorating conditions.

a. What changes in plasma levels of energy substrates would occur in the first 3 days of his fast?

b. On what immediate and on what ultimate sources of energy would brain metabolism depend?

c. What role would the liver play in providing energy sources to the brain and muscles?

d. What early changes in plasma levels of hormones would occur? How would this regulate his energy metabolism?

e. What physiologic events would occur when he stopped his fast by drinking a large quantity of a high glucose fluid?

Answer 1

a. There is a change in plasma level of insulin and glucose during first three days of fasting. Also an elevated level of fatty acids and ketone bodies are observed along with increased secretion of glucagon.

b. Glucose is the prmary energy source of brain. Once glucose gets depleted, the majority of energy needs are met by ketone bodies.

c. Liver produces more of ketone bodies by process called ketogenesis throughfatty acid β oxidation in hepatic mitochondria. Liver also enhances conversion of glucose froms tored glucagon. Since because that citric acid cycle is unable to oxidize the acetyl units from fatty acid metabolism, it increases the synthesis of acetoacetate and d-3-hydroxybutyrate from acetyl CoA. The metabolism gets shifted to gluconeogenesis that depletes the oxaloacetate that is critical for citric acid cycle.

d. Change in the plasma hormone level of insulin, epinephrine and GH during influence the breakdown of body fat and facilitate its use for energy. It diminishes glucose uptake and enhance FA uptake which halts the conversion of pyruvate into acetyl CoA. It further promote the export of pyruvate, lactate, and alanine into liver for converting them into glucose.