Research overview: protein and fat as primary energy substrates in fasting and feeding

Cats fuel themselves chiefly with protein and fat, and this overview reviews how they use these substrates in feeding and fasting. With limited reliance on carbohydrate, cats draw energy from dietary and stored fat and from amino acids, and during fasting they mobilise these reserves, a process that can stress the liver if a cat stops eating abruptly. Their metabolism assumes a steady protein supply. Researchers study substrate use through metabolic measurement and clinical observation. Why it matters: understanding feline fuel use explains both normal energy metabolism and risks such as hepatic lipidosis, a dangerous fatty-liver condition that can develop when overweight cats stop eating. It ties the cat protein-and-fat metabolism to practical health concerns and shows how a metabolism optimised for prey copes, sometimes poorly, with disruptions to feeding.