FIT for LIFE Knowledge Base

Briefly explained: Fat and Carbohydrate Metabolism

Two important terms in endurance sports are fat metabolism and carbohydrate metabolism. They are often confused, however. What is the respective meaning?

Carbohydrate metabolism (= glycogen metabolism, sugar metabolism) provides about twice as much energy per time as fat metabolism, but fats burn much longer and are practically unlimited in the body, while glycogen reserves only last for about 90 minutes of exercise. The differences between the two systems can be interpreted similarly to burning something at a medium or low flame.

When we run for about an hour at medium-high intensity, our body mainly uses glycogen, i.e. carbohydrates. The body or muscle tries to use the most favourable mixture for energy supply, depending on the intensity. If we run for two or three hours at a moderate pace, energy is obtained mainly from fatty acids. Fat metabolism is the ‘diesel engine’ of our body.

In most endurance training, the two combustion processes are side by side and one does not exclude the other. Depending on the intensity and duration of training, either carbohydrate metabolism (more intense and shorter sessions) or fat metabolism (less intense and longer sessions) prevails. Due to the dominant proportion of fat metabolism in moderately intense and long training sessions, this form of training is also called fat-burning training and is used for long-term weight control. Although it should be noted that the actual number of calories burned during intense sessions is naturally much higher than during less intense sessions of the same duration. However, high intensities cannot be sustained over a long period of time, so it makes perfect sense to do long, low/moderate intensity sessions on a regular basis.


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