Catabolic Response to Injury
During illness or after trauma, food intake frequently falls. However, despite this decline in intake, the adaptive responses to starvation do not occur. In contrast to PCM, in humans and laboratory animals, the metabolic response to injury (critical illness, sepsis, trauma, surgical manipulation, etc.) is characterized by an increased metabolism and the onset of a catabolic process leading to excessive breakdown of tissue proteins.
There is a preference to use amino acids from the breakdown of skeletal muscle proteins as a metabolic fuel, in contrast to PCM in which fat is the principal source of energy. The adaptive switch to fat utilization is limited due, in part, to increased concentrations of circulating insulin. Insulin resistance develops, and hyperglycemia may occur despite the absence of food intake. This metabolic state is the result of a complex interaction of inflammatory cytokines, circulating hormones, and neurotransmitters and is designed to provide endogenous substrates for gluconeogenesis, wound healing, immune cell replication, and synthesis of acute-phase proteins.1 Although this response is beneficial, long-term muscle breakdown results in loss of muscle strength, visceral organ dysfunction secondary to loss of structural and enzymatic proteins, impaired wound healing (due to loss of precursors for wound healing), immunosuppression, and compromise to the patient's overall health.As sodium retention and water retention are components of this response, weight loss and muscle wasting frequently go unnoticed. Food deprivation during this hypermetabolic/ catabolic state results in a much greater loss of lean muscle mass and visceral protein than would be expected during simple starvation. The metabolic adaptations to starvation in a healthy human can result in a 75% decrease in protein loss, whereas the metabolic responses to critical illness result in an increase in energy expenditure and protein metabolism.
Although nutritional supplementation can reverse the catabolic processes occurring during simple starvation, it will not completely reverse those occurring during metabolic stress because as long as tissue injury persists, catabolic processes are maintained.
More on the topic Catabolic Response to Injury:
- Catabolic Response to Injury
- Smith Bradford P., Van Metre David C., Pusterla Nicola (eds.). Large Animal Internal Medicine. Part 2. 6th edition. — Elsevier,2020. — 2279 p., 2020
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