Prof. Köhler, you conduct research on the question of how sport affects people's body weight. What are your findings?

We have found that sport alone is very good for maintaining weight and not gaining weight, but not at all for reducing kilos. Our research shows that a few lose weight well with exercise, but at least as many actually gain weight with exercise. The majority lose weight very marginally with exercise - but not to the extent they would like or to the extent that would be medically appropriate. 

You say that, among other things, "compensatory eating" gets in the way of us using exercise to lose weight. What do you mean by that?

People who exercise more tend to adjust their eating patterns. We call this "compensatory eating." This has to do with our psyche, which wants to reward us for the effort, but also with appetite-regulating hormones that are released after exercise and trigger the feeling of hunger. Many people then have a particularly strong appetite for sweets and fatty foods and reach for pasta, burgers and the like, which quickly replenishes the calories consumed.

Doesn't that also depend on how much exercise someone does?

If you want to lose weight, you have to burn more calories than are supplied to the body. To lose weight with sports, you would have to do an insane amount of sports. But we also know today that more physical activity does not mean higher calorie consumption. This has to do with an adjustment of the metabolism. Losing weight through diet offers much more room for maneuver: if you're not a competitive athlete, you use an average of about 30 percent of your energy through sports, while it's 100 percent through diet.

How is it that metabolic adaptation makes it difficult for us to lose weight with sport alone?

We have the problem that the body resists giving up reserves. That's why I feel hungrier when I exercise. If I also restrict my diet and don't give in to hunger, the body reacts by shutting down metabolic processes that are not essential. In other words, it adapts to the new situation and readjusts itself. This is shown by data from our experiments. In evolutionary terms, this is very clever and was necessary in the days of hunter-gatherers to ensure human survival. Today, it stands in the way of us losing weight. The greater the deficit, the more I put the body in distress so that it shuts down these metabolic processes.

How can someone tell that such a metabolic adjustment has occurred?

Theoretically, you can tell by eating less than you ideally could. If I maintain my weight, that means I am in balance. However, this does not automatically mean that I have secured the optimal energy supply. Indicators that this is not the case are that someone is always tired, tends to have infections, is constantly cold, or even if women do not have their period. However, without measuring resting metabolic rate, as we do in our examinations, metabolic adaptation is very difficult to diagnose.

Prof. Köhler, what are your most important tips for losing weight?

• Be patient and don't expect miracles. If you lose a lot of weight quickly, you often put on a lot of weight again quickly. Half a kilo a week or even less is therefore a good target. If it is more, the risk increases that the metabolism gets used to the emergency and it does not work with losing weight.
• Exercise, especially to prevent gaining weight back in the end. Everyone can lose weight relatively well in the beginning. Keeping the weight off is the greater art.
• Watch what you eat. It is helpful to think about what you want to eat afterwards before you start exercising. The decision is then less impulsive and you are more likely to reach for foods with a high nutrient density and low energy density after the workout, such as vegetables, fish or lean meat, and forgo the quick kebab on the way home from the gym. 

Is there a type of diet that you prefer for losing weight?

To lose weight, you need a calorie deficit, and whether this is achieved through low-carb or intermittent fasting, for example, is irrelevant at first. However, I myself am a friend of the Mediterranean diet, as recommended by the German Nutrition Society (DGE), because this balanced diet is evidence-based, i.e. proven to be healthy.

Prof. Köhler, thank you very much for the interview.

To the homepage of the Assistant Professorship of Exercise, Nutrition and Health

Contact:

Prof. Dr. Karsten Köhler
Assistant Professorship of Exercise, Nutrition and Health
Connollystr. 32
80809 München

Tel.: 089 289 24488
E-Mail: karsten.koehler(at)tum.de

Text: Gianna Banke
Photos: georgerudy/AdobeStock, Andreas Heddergott/TUM