Deprivation, frustration, yoyo effect ... So many consequences related to the regimes that Sandra Aamodt, American neurobiologist, tries to demonstrate as being vain in his book "Why diets make you fat" (Hugo Doc) published on February 16th.

Based on scientifically established data (studies sourced and crossed in notes), her knowledge of neuroscience and human biology, the author, herself overweight and subscribed to various diets for many years, tries to to reconcile with one of the most natural and vital acts of all: to eat.

Passages chosen to finally understand why the long-term failure rate of a diet varies between 80 and 95%.

Diets are ineffective because: the brain has a target weight range

"The brain system of weight regulation has two main priorities: body weight must remain stable and it must not fall too much. Throughout the history of humanity, or almost, these two objectives were perfectly sensible (starvation being a lot worse than obesity). But in modern life, marked by an abundance of high-calorie food, the second priority has become problematic for many people. Efforts to undermine brain resistance to weight loss often end up increasing the influence of external stimuli such as advertising, which encourages bulimia.

Often, if people are obese, it's because their brain considers that weight is right for them.

If a person with an initial weight of 60 kg diets to 40kg, his brain will declare a state of emergency and use all the means at his disposal to bring the weight back to normal. "

"Contrary to popular belief, the process does not seem to be reversible. Maintaining body weight below the target range, even for years, does not encourage the brain to consider this thinness as a new goal. This persistence is the fundamental reason that makes it difficult to maintain weight loss. "

Worse, says the author a few lines later:

"It has been shown that instead of losing weight, diets put people on the road to weight gain. In four years, two out of five plan members end up weighing heavier than before. Since diets are more likely to make people fatter than to lose weight in the long run, the prevalence of diets in recent decades may well be a cause of rising obesity. "

Diets are inefficient because: the energy system watches over grain

"Many people think that diets are a simple conflict between will and temptation when in fact it involves multiple brain systems, each with its own priorities. The energy balance system (the weight thermostat) tries to keep our weight within the weight range targeted by the brain, while the hedonic (reward) system pushes us to eat high calorie foods .

When our weight returns to the weight range targeted by the brain, the energy balance system calms down and our appetite returns to normal. But because of the time we spent suppressing and ignoring hunger, we became less responsive to the signals that tell us to stop eating. This is the opportunity that the reward and usual systems were waiting for to intervene and take things in hand, which leads to even more weight gain "

Diets are ineffective because they stress us!

"The stress generated by dieting or body dissatisfaction often causes weight gain and therefore even more stress. People who are at the base end or below the right weight usually lose weight when stressed, while those at the high end or above the normal weight range are more likely to get fatter. .

Since the brain does not give any importance to the reason that a person is eating less - a scarcity or a diet have the same effect on the energy balance system - it is not surprising then that a diet increases the release of stress hormones. Stress causes weight gain because stress hormones encourage eating by increasing appetite and reducing the effectiveness of satiety signals (...) The release of endogenous opioids amplifies the reward power of the appetizing food. so that the sequence "stress encourages food to comfort" is likely to be retained and repeated. "

This is the infernal cycle: diets stress people, which makes them gain weight, especially after the end of the diet.

Diets are ineffective because: the microbiota influences weight gain

"The microbiota has extensive effects on the energy chains of the body and the relative abundance of different species of bacteria varies according to the weight of the body (...) the species Helicobacter pillori was the most widespread in the stomach since the Antiquity and it accounted for more than half of the bacteria in the stomach. But for a century its presence has greatly decreased among people in developed countries around the world (...) the disappearance of this species also changes the production of hormones involved in the regulation of appetite (...)

The eradication of H. pylori by antibiotic treatment in adults is often associated with weight gain compared to cases where the same antibiotics failed to eliminate their target. "

Diets are ineffective because: genes ...

"Weight is as hereditary as size, although it is easier to detect the genetic influence on the size because it does not change much in adulthood (...) In some people, damage to a particular gene directly affect the weight by preventing the production of a protein that is required for the proper functioning of the energy balance system.

But, more generally, genes affect the development of the body, especially the brain, which influences weight control in adulthood. "

"Why diets make you fat" from Sandra Aamodt, Hugo Doc, 18,50 euros.