Biochemistry of Starvation
Starvation occurs when the human body stops taking food or both food and water. It is a type of metabolic stress condition of the body. There are many conditions when your body can be under starvation, like due to food scarcity during natural calamities like floods, droughts etc. When there is extreme poverty, during clinical conditions like major surgeries and in severe burns, during dieting in the desire to lose weight, and in hunger strikes. The human body can survive without food maximum up to 65 days.
During starvation, the body will start lacking calories which include carbohydrates and lipids, proteins, vitamins and minerals, antioxidants. During starvation, there is an increase of glycogenolysis, gluconeogenesis, lipolysis, and ketogenesis. Brain in starvation uses ketone bodies as an energy source than using glucose, that’s why our brain functions for few weeks even in starvation.
Insulin is decreased in blood and glucagon, epinephrine and norepinephrine levels are increased. The adult 70 kg human has 8,000 Kilojoules of glycogen stored which is consumed in 24 hours during starvation. There is shutting of lipid-derived energy in glucose to peripheral tissue and lactate goes back to the liver to form again glucose. This is how the body adapts when glucose levels are decreased.
The major source of energy comes from triglycerides. The 70 kg adult human has 400,000 Kilojoules stored in adipose tissue. Lipolysis occurs and lipids are converted into fatty acids. Fatty acids undergo beta-oxidation in mitochondria. Then acetylcholine is formed which enters the citric acid cycle and Adenosine triphosphates (ATP) is formed and this ATP forms glucose by gluconeogenesis.
Ketogenesis occurs which converts fatty acids to short chain fatty acids and ketone bodies. During ketogenesis, there is the formation of acetoacetate which readily converts to acetone, and this acetone gets released from urine and lungs produces “acetone breath”.
In 8-10 days of fasting, body weight is reduced to half and in later time skeletal muscles are degraded. In the last stage, autophagy occurs where cells start to eat up the critical molecules to continue the process of gluconeogenesis. Due to this structure of cells is disturbed and finally starvation leads to death generally due to diaphragm failure as a result of prolonged autophagy.