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Catabolism occurs when you digest food, the molecules are broken down in the body into smaller and simpler units so they can be used to release energy.

When you’re in a catabolic state, you’re breaking down or losing overall mass, both fat and muscle.

This metabolic pathway uses four hormones:


In preparation for physical activity, adrenaline aids in the mobilisation of energy reserves in the form of glucose and free fatty acids.


Cortisol increases fuel availability by mobilising glucose, free fatty acids, and amino acids from glycogen stores and skeletal muscle. Overproduction of cortisol lowers lean body mass and muscle mass while possibly increasing energy expenditure.


Overeating and excessive physical activity changes the cytokine secretion, affecting metabolic and immune regulatory pathways that cause or facilitate metabolic disorders. These cytokines are part of a complex network that allows organs and tissues to communicate with one another (e.g., adipose, liver, muscle, skeleton)


Glucagon is a hormone that works in opposition to insulin by increasing blood glucose levels by stimulating hepatic glucose production.

The three catabolic processes and reactions


The metabolic pathway that converts glucose to pyruvate and a hydrogen ion is known as glycolysis. This process releases free energy, which is then used to create the high-energy molecules ATP.

The citric acid cycle / Krebs cycle

All aerobic organisms use the Krebs cycle to release stored energy by oxidising acetyl-CoA obtained from carbohydrates, fats, and proteins.

The electron transport chain

The electron transport chain is a group of proteins that transfer electrons through a membrane within mitochondria to create a protons gradient that drives adenosine triphosphate synthesis (ATP).

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