Swimming, running, pedaling or jumping does not melt superfluous bulges. This received idea has a hard life because biology and arithmetic are confused .

If our caloric intake is higher than our energy expenditure, the needle of the scale is inclined to the wrong side. But the opposite is not so obvious.

With sport, the body loses most of the water

When you weigh yourself after an hour of zumba, the miracle seems to have worked. Several hundred grams flew away. But be careful, it's just a lure. Indeed, "the weight lost after such physical effort is essentially by sweating," said Florence Pujol, nutritionist author of "I eat and I am good" (Ed Puf).

In other words: the beads have not emptied. The body has lost almost only water (and mineral salts), which will be immediately recovered during rehydration.

To support a sports activity, the body starts by drawing its fuel in glycogen reserves housed inside the muscles and liver. It attacks the fat mass only afterwards. Unless you're a professional athlete or run the Paris Marathon, the fat tissue is not reduced .

Exercise: the mirage of calories burned

The calorimetric meters of gym equipment, which indicate the number of calories burned on the machine, are larks' mirrors. When their screen displays "- 120 calories", we shout victory because the loss seems huge. But, in reality, it's insignificant, the equivalent of a fruit yoghurt .

Contrary to what one thinks, the sport does not cause big expenses of energy. One kilometer (km) of walking only "grills" 65 Kcal on average. To lose a kilo a month, it would be necessary to walk 138 km in 30 days, or more than 4.5 km per day! A challenge that few of us are ready to meet.

A jog at moderate speed (8 Km / h) is meanwhile spend 80 Kcal per kilometer. To get rid of a kilogram of fat, you'd have to run ... twelve hours straight .

Similarly, two hours of swimming equals energy in terms of an apple tart and two hours of cycling to a chocolate loaf. It is obvious, given these few figures, that sport rarely makes you lose weight.

Moving changes the relationship to food

As demonstrated by Dr. Timothy Chruch of the University of Louisiana, there was little difference in weight after six months between women who practice 1h, 2h or 3h of sports per week and those who do not do it at all. Not only is the number of calories dissipated is small, but "women also tend to offset the effort provided by a slightly higher food intake," says the researcher.

Physical exercise induces an increase in the secretion of ghrelin, the hormone that governs the appetite. But sport also increases the production of serotonin, the hormone of serenity . As a result, it dispels psychic tensions and alleviates the conflicting relationships that many have with food. Cravings faint , so we stop gaining weight. It's already that !

Sport and weight loss: a long-term indirect effect

Regular physical activity improves lung capacity and cardiac pump performance over time. It also develops gradually muscle mass.

In the long run, even if the scale does not move one iota, the fat eventually melts because the more muscles we have, the higher our energy costs at rest. A loss of weight then begins in the long term ... provided you fill up with good protein and put the soft pedal on the sugar.