Fat burning

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Fat burning , more precisely fatty acid oxidation , is the name given to those chemical reactions in which a fatty acid releases one or more electrons by reacting with an electron acceptor. In addition, the metabolic pathways α-oxidation , β-oxidation and ω-oxidation , which are part of the energy supply of the body, are summarized in biochemistry under the term fatty acid oxidation . Here the β-oxidation plays the greatest role.

Energy turnover

In fat digestion , fatty acids are obtained by breaking down fat . They are then fed to the fat metabolism and are available to the body for energy turnover. The fat can come from food as well as from the body's own fat tissue . The calorific value of pure fat is 39 kJ / g (9.3 kcal / g). Adipose tissue does not consist of 100% fat and therefore has a lower calorific value (approx. 7 kcal / g).

Fat oxidation is an ongoing process in the body. The extent depends on the degree of physical activity and thus on the energy requirement. Further influencing factors are the level of training, gender and the composition of the muscle fiber types of the stressed muscles. Type 1 muscle fibers tend to work more on fat, while the faster type II muscle fibers need carbohydrates rather than fuel. Studies have shown that a high-carbohydrate diet reduces fat oxidation during subsequent exercise by up to 35%. The reason for this is that the ingested carbohydrates are first absorbed and metabolized by the muscle cells. The effect can last up to eight hours after eating a meal.

Burning fat in sports

Athletes and doctors often take the view that the body draws its energy predominantly from stored body fat when exercising in a certain intensity range . This intensity range is individually different and should be between 60% and 75% of the individual maximum heart rate . While glucose is primarily metabolized at first, fat burning increases to a certain level that is characteristic of the intensity within the first half an hour after the start of training.

The opinion that glucose is primarily burned at the beginning of training is now controversial. Nowadays it is assumed that the percentage of fat burning depends solely on the strength of the load and the general state of training.

According to specialist studies, the amount of fat burned through exercise depends on several factors, including the level of athleticism in the body and the development of muscles. Men burn less than women with the same intensity of exercise. Obesity and insulin resistance reduce consumption. In studies, the fat metabolism of trained people was most effective at an exercise intensity of 65%, and untrained people at around 50% of maximum performance.

Energy is always "consumed" (or converted into another form of energy) from the first minute, especially during sport, depending on the intensity. With moderate load, the "consumption" is lower than with high. The decisive factor for weight reduction is not how much fat has been "burned" during physical activity, but the energy balance , i.e. H. how much energy is “consumed” in total.

In the case of extensive exercise (e.g. endurance run), aerobic energy production consists of burning fat and carbohydrates (oxidation of free fatty acids and glucose) from the start, in contrast to anaerobic energy production during short-term peak loads, e.g. B. the sprint . According to studies, lipid oxidation (fat burning) is stronger when jogging or walking than when cycling.

There is no scientific evidence that a dietary supplement advertised as a fat burner would increase fat burning.

Exercising regularly is the only effective way to increase the metabolism of lipids during exercise. Endurance training in particular leads to an improved supply of the muscles with enzymes for fat metabolism. In addition, the mitochondrial density is increased and the local blood flow is improved, both of which have a beneficial effect on fat oxidation.

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  1. ↑ a b c d Asker E. Jeukendrup: Fat burning and physical activity , in: German Journal for Sports Medicine, No. 9, 2005 (PDF; 71 kB)
  2. ↑ Kurt A. Moosburger: "FAT BURNING" IN SPORT: MYTH AND TRUTH (PDF; 63 kB)

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