Prof. Dr. Karsten Köhler, head of the Assistant Professorship of Exercise, Nutrition and Health, was featured in a TV report of the program "Doc Fischer" of the Südwestrundfunk (SWR) on January 17, 2022. Under the title "Losing weight - why it often doesn't work with sports alone", the nutritionist commented on the extent to which sports contribute to weight reduction at all.
"Cravings after sport, or so-called compensatory eating, are about me replenishing at least some of the energy I consumed during sport through food after sport, thus making up for this deficit," said Prof. Köhler. "Certain appetite-regulating hormones play a role in this, but also, for example, the blood sugar level or psychological factors such as reward. In the end, in evolutionary terms, it's again precisely about the fact that it's a mechanism of the body to compensate for an energy deficit and to avoid losing weight or muscle mass."
As part of the TV report, the metabolism of sports student Lilli Schlage was analyzed because, in addition to cravings, the body also defends itself against weight loss after exercise by changing its metabolism and, for example, lowering the resting metabolic rate. This is then referred to as a metabolic adaptation.
"A metabolic adaptation basically means that the body lowers its energy metabolism by certain functions in order to save energy," explains the nutritionist. "First of all, this is not dependent on what exercise I do, but how much exercise I do, and rather also how much energy I convert. In general, we can calculate that if we have an energy deficit of about 500 calories a day, there are very likely no metabolic adaptations. But if we're targeting 1,000 calories or even more a day as an energy deficit, then it's pretty certain that our metabolism is shutting down, conserving energy, and thus compensating for the energy deficit."
In the case of sports student Lilli Schlage, an analysis of her breath was therefore to be used to determine whether the body had already shut down her metabolism and how many calories she was still burning at all at rest.
"For the resting metabolic rate measurement, the test subjects are placed under a plastic hood so that we can measure the composition of the air, i.e. what carbon dioxide is exhaled and what oxygen is inhaled again," explains Karima Sophie Kirchner, Research Associate at the Assistant Professorship of Exercise, Nutrition and Health. "This allows the exact composition of the respiratory gases to be analyzed, from which the respiratory quotient can be calculated. Based on this, a statement can be made as to whether more fat or carbohydrates are burned. From this, the resting metabolic rate can then be calculated."
In addition to metabolic adaptation, fat burning can also play an important role in losing weight through exercise.
"In order to mobilize fat deposits or the body's fat reserves, we need to get the body into a state in which it gains energy primarily through fat oxidation," explains Prof. Köhler. "This happens mainly at moderate intensities, such as running at a pace where you can still talk. Here, the heart rate, i.e. the pulse rate, is not yet so high and the body just falls back on these fats. When I'm exercising at higher intensities, the body tends to fall back on carbohydrates, which are more readily available, but they're not stored in fat tissue."
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Contact:
Prof. Dr. Karsten Köhler
Assistant Professorship of Exercise, Nutrition and Health
Georg-Brauchle-Ring 60/62
80992 München
phone: 089 289 24488
e-mail: karsten.koehler(at)tum.de
Text: Romy Schwaiger
Photos: SWR program „Doc Fischer“