Fettbruk

Fettbruk is the use of fat as an energy source in human metabolism. It describes how the body oxidizes fatty acids derived from dietary fats, adipose tissue stores and intramuscular triglycerides to generate ATP. Fat oxidation occurs alongside carbohydrate oxidation and becomes more prominent during lower‑intensity exercise, longer duration activity, fasting or caloric restriction.

The metabolic pathway starts with lipolysis in adipose tissue, releasing free fatty acids and glycerol. Free fatty acids bind to albumin and are transported to tissues such as muscle and liver, where they are taken up and activated to fatty acyl‑CoA. They are then transported into mitochondria via the carnitine palmitoyltransferase system and undergo beta‑oxidation, producing acetyl‑CoA that enters the citric acid cycle and oxidative phosphorylation to form ATP. In the liver, acetyl‑CoA from fatty acids can be used to produce ketone bodies when carbohydrate availability is low.

Fettbruk is regulated by energy demand, training status and diet. Hormones play a key role: insulin inhibits lipolysis, while catecholamines, cortisol and growth hormone promote it. Carbohydrate availability influences fat oxidation; higher fat availability and certain dietary patterns can increase fat use at submaximal intensities. The respiratory exchange ratio (RER) measured by indirect calorimetry provides an estimate of fat versus carbohydrate oxidation, with values around 0.7 indicating predominantly fat oxidation and around 1.0 indicating carbohydrate oxidation.

Applications and relevance include endurance performance optimization, weight management and metabolic health. Fettbruk varies between individuals and can be assessed through indirect calorimetry and blood biomarkers, contributing to diet and training strategies.