Metabolic responses of body to stress and starvation

The human body like other animals behave differently towards stress and starvation. Here is the summary of the physiological and Metabolic responses of body to stress and starvation (absence of nutrition) 

The metabolic response to starvation

The first metabolic response to starvation is that the body switch from carbohydrate metabolism to that of fat catabolism, in the context of a hypometabolic state, with minimized catabolism.

Initially, the precursors of carbohydrate stores (eg. glycogen) are depleted.

Then, during the first 24-48 hours there is enhanced gluconeogenesis in the body from amino acids and glycerol.

Subsequently, after 48 hours ketogenesis takes over, and most of the metabolic needs of body are met by ketone bodies and free fatty acids. 

Consequently there is decrease level of insulin levels, and relatively increased influence from catecholamines and cortisol.

Over prolonged starvation of many days, protein catabolism start , which result in the degradation of structurally important proteins leading to organ system dysfunction.

The metabolic response to stress

The metabolic response to stress is somehow different from that of starvation. The metabolic response in stress is mediated by some important catabolic hormones (e.g. glucagon, catecholamines and corticoids). This further augmented by eicosanoids, cytokines, oxygen radicals, other local mediators and insulin resistance. The stress response of body can only be effectively reversed by taking following measures. 

1. Reducing the infection. 

2. Control of inflammation. 

3. Minimizing heat loss. 

4. Good Nutritional support

5. Psychological support may have an important role

The key difference between metabolic response to starvation verses stress

The key difference between metabolic response to starvation is different to that stress. The he main features are illustrated as follow

Resting energy expenditures. The resting energy expenditure is decreased in starvation well in case of stress resting energy expenditures are increase

Mediator Activation. There is no mediator activation involved in case of starvation while in case of stress there is involvement of mediator activation

Respiratory quotient. The respiratory quotient is decreased(0.6—0.7) in starvation while in stress it is increased(0.8—0.9)

Primary fuels. The primary fuel in starvation is fat while in stress it is mixed

	Postprandial State	Starvation (Prolonged)	Stress
Lipolysis in fat tissue	↑↑	↑↑↑	↑↑
Lipid oxidation	↓	↑↑↑	↑
Ketogenesis	↓↓	↑↑↑	↑

Proteolysis. Initially there is no proteoolysis in case of starvation but occurs in prolonged starvation but in case of stress there is always proteolysis

	Postprandial State	Starvation (Prolonged)	Stress
Proteolysis	↓	↓	↑↑↑
Proteosynthesis	↑	↓	↑↑
Amino acid oxidation	↑	↓	↑↑↑

Branched chain oxidation. There is marked branched chain oxidation in stress compare to starvation.

Hepatic protein synthesis. There is less hepatic Protein synthesis in starvation but in stress there is marked hepatic protein synthesis

	Postprandial State	Starvation (Prolonged)	Stress
Gluconeogenesis	↓	↑	↑↑↑
Glycolysis	↑	↓	↑↑↑
Glucose oxidation	↑↑↑	↓	↓
Glucose cycling	↑	↓	↑↑↑

Ureagenesis. There is more urea production in stress compared to starvation.

Urinary nitrogen loss. There is more nitrogen loss in stress compared to starvation. 

Gluconeogenesis. There is more need for glucose in stress Stress so the glucose production increases in stress compared to starvation where the main fuel is fat.

Ketone body production. Because the main body fuel in starvation is fat so the ketone body production increases in starvation but in stress there is less production of ketone bodies

All this can be illustrated in figure below

Key difference between metabolic response to starvation and stress