A team of researchers provided an overview of human metabolism, increasing its various pathways and clinical aspects, according to a study published in Surgery. On lipid metabolism, fatty acids are typically used for energy production in oxidative tissues.

“Since they are amphipathic and potentially toxic, their plasma concentration does not rise to more than ~0.5 mM physiologically and they are transported bound to albumin (‘free’ fatty acids are more correctly termed [non-esterified fatty acids]),” the authors said.

When the genes that encode these fatty acids undergo abnormal mutations, a condition known as long chain fatty acid oxidation disorder (LCFAOD) can occur, resulting in impaired fat metabolism.

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The word “metabolism” comes from the Greek word “to change.” In medicine today, metabolism is the sum of the biochemical reactions that generate important biological functions, such as muscular contraction, heat and energy generation, and homeostasis.

Because there are many intricate processes that can constitute “metabolism,” Evans and Heather chose to highlight a few key processes. One, for example, is carbohydrate metabolism, which is a complex series of chemical reactions involving glucose, glycogen, lactate, ketones, and more.

“Sympathetic activation and several hormones, including catecholamines, cortisol and growth hormone, stimulate hepatic glycogenolysis and gluconeogenesis, with glucose release into the blood, but glucagon is the major catabolic signal, raising blood glucose by stimulating hepatic glucose production and inhibiting the reciprocal anabolic pathways,” they said.

Read more about LCFAOD etiology

The last aspect of metabolism highlighted by Evans and Heathers is amino acid metabolism. Insulin is the main anabolic signal that regulates protein metabolism, stimulating proper protein synthesis and inhibiting proteolysis. 

However, occurrences such as trauma, sepsis, and burns can impair the proper functioning of metabolism in the body. “Failure of the body to adequately counter the primary pathological insult and to regulate its response to it leads to multiorgan failure and/or critical illness myopathy/polyneuropathy, with substrate depletion and wastage,” the authors concluded.


Evans RD, Heather LC. Human metabolism: pathways and clinical aspects. Surgery. Published online February 18, 2022. doi:10.1016/j.mpsur.2022.01.004