We don't know enough, but lack of sleep and weight gain are strongly linked.

Dr Jimmy Mohamed, columnist at Europe 1, explains Friday the mechanisms that lead to this link.

And give some advice to sleep better… and therefore lose weight better.

>> The holidays have been over for several days, so it is time, if not yet, to reset your sleep.

Not to be tired, of course, but also to avoid being overweight.

Because as Dr Jimmy Mohamed confirms to us on Friday morning on Europe 1, the quality of sleep and weight gain are closely linked.

>> Find Europe Matin in replay and podcast here

"We know that one in two French people are overweight and that 30% of French people are not satisfied with their sleep. However, to lose weight, you must already sleep well, and vice versa. Lack of sleep is an often ignored cause of weight gain.

There is a physiological explanation.

When you don't sleep at night, you stress your brain.

You're going to kind of make him angry and secrete more cortisol.

Cortisol will cause what is called lipogenesis, that is to say the production of fat cells and therefore, inevitably, this fat will accumulate in a particular place in the belly.

And this fat is responsible for metabolic complications like diabetes.

800 grams in four nights

In addition to that, we know that a lack of sleep will make you no longer secrete a hormone called ghrelin.

This hormone is used to increase your feeling of hunger and therefore you will be more hungry.

And conversely, the hormone that's supposed to fill you up, leptin, well you secrete less.

The result: you eat more, and you eat more starchy foods and sweets.

Obviously, that it is not towards the carrots on which one will throw.

And the weight gain can go very, very fast.

Study shows that in four nights, if you lack sleep, you get four hours of sleep per night and you could put on 800 grams.

800 grams in just four nights.

Above all, what is worrying is that 20% of 15-25 year olds sleep less than 5 hours per night.

The 7x7 rule

And the worst part is that at an equivalent diet, if you decide to lose a little weight, those who sleep less than six hours a night lose fewer calories than those who go to sleep normally.

This means that a lack of sleep, at a rate of one hour less per night, is enough to gain weight and gain weight and lose less.

On sleep, there is a very simple rule.

You already know that we eat five fruits and vegetables a day, that we must drink a maximum of two glasses of alcohol and not every day.

Well for sleep, you have to remember that it is 7x7.

You need seven hours of sleep, seven days a week.

It's been 49 hours. "