Is it the endorphin that increases appetite after physical exercise? The debate was not settled, including on the reality of this “post-sports” hunger. Some will tell you that they are hungry after a ten-minute walk, others have their appetite cut off by an effort of more than an hour.
The discovery of the role of endorphins in sport dates back to the 1980s. These are hormones secreted by the brain. The ending “orphine”, which recalls the word “morphine”, is not there by chance. Our body is indeed a large-scale “dealer”. Endorphins have a dual role: it is, above all, a painkiller. The prolonged physical effort required by man to adapt to his environment takes place in a context of pain, particularly for muscles and joints. The endorphins are there to reduce the intensity. Life having unquestionably become more comfortable, at least in industrialized countries, it is the second role of these hormones which is today the most important. Endorphins participate in what is called the “reward circuit”. Like real morphine, which arouses, by calming, an exceptional feeling of well-being, endorphins are responsible for the feeling of happiness caused by prolonged physical effort. It takes at least a good hour to start feeling the effects. But, like morphine, they would induce a phenomenon of dependence! A top athlete can easily bear pain during exercise, but intensive training can turn into real addiction: overtrained athletes often have an irrepressible urge to exercise, with a frequent escalation of the “dose daily, to obtain the best secretion of this hormone.
Is it the endorphin that increases appetite after physical exercise? The debate was not settled, including on the reality of this “post-sports” hunger.
Research has given a scientific answer, thanks to MRI techniques. We know perfectly well the areas of the brain that control the pleasure of eating and manage the quantity necessary for the disappearance of the feeling of hunger. MRI makes it possible to “see” what is called the reward circuit in the brain. The results are in favor of physical activity, appetite limiter.
It seems that physical exercise modifies the food reward circuit by reducing the quantity necessary but, above all, by favoring less fatty, less rich foods.
The experiment consisted of taking two groups of volunteers. The first remained in front of the television; the other got one hour of physical activity. Then everyone was put in front of an “all you can eat” buffet. The inactive ones spontaneously went to foods high in sugar and fat. The “athletes”, confirmed by the MRI study of their brains, saw their reactivity to food signals significantly reduced. The areas managing the quantity and the reward circuit remained calm, even in front of the desserts, while they were awakening in the idlers! The only criticism that can be leveled at these results is that they only concern people with a so-called normal weight. Studies in obese people are not as obvious, probably because the mechanism of overconsumption in them is more complex and the sight of food increases the feeling of hunger tenfold, making physical exercise a very useful pretext. However, if a few years ago scientists thought that everything was under the control of hormones, we know today, and this is important news, that the brain is sensitive to exercise and can react change the hunger message by decreasing it. The enemies of sport will come up with arguments like: “45 minutes of walking for a 70-kilo man represents an expenditure of around 300 kilocalories, the equivalent of a butter croissant with a little jam”, summarizing the Exercise with a simple reduction in caloric intake is reductive and only presents a very partial version of the interest of daily practice.
In conclusion, the impact of physical exercise on hunger depends on each person’s personality, the amount and the repetitiveness of the effort.
Doctor Jean-Francois Lemoine
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