Who has never feasted in advance by inhaling the aroma of a good little dish simmering on the fire? Food smells are a big part of the pleasure of eating, but they also have an adverse effect on our weight: they help us store the fat we eat rather than burn it.
In a study published in Cell Metabolism, researchers gave food to mice that had lost or retained their sense of smell. They found that the former lost weight – and only fat, not the muscle or tissue needed – while the latter took it, for the same food intake. Other mice with an overdeveloped sense of smell grew even fatter on a fatty diet than the normal smelling mice. Results that lead scientists to ask the question of food odors in humans.
The key would be in the brain
Humans who have lost their sense of smell as a result of age, illness or accident are known to eat less or even become anorexic. But the causes are not very clear because loss of smell often causes depression which leads to loss of appetite. This new research seems to point to a direct effect of the loss of smell. The smell of what we eat would thus play a role in the way in which the body uses the calories ingested.
Celine Riera, a former post-doctoral fellow at the University of Berkeley in California, explains that “mice like humans are less sensitive to smells when they are full than when they are hungry. The lack of smell in a dish could suggest to the body that it has already eaten and that it can therefore stop storing new calories and, on the contrary, burn them ”. “The sensory system plays a role in metabolism. Weight gain is not just a question of calories ingested, it is related to the way in which these calories are perceived ”, adds Andrew Dillin, senior author of the study. In the brain, the area of smell and that managing the metabolism would thus be connected.
Melt fat
When the researchers temporarily destroyed the olfactory neurons in the mice, the mice quickly burned calories by regulating their sympathetic nervous system, known to increase fat loss. Rodents converted beige fat (subcutaneous fat located on the stomach and thighs) into brown fat, known to burn fatty acids and turn them into heat. Some mice have thus transformed almost all of their beige fat into brown fat, becoming somewhat of a burning machine, with a healthy weight. The same goes for the white fat that surrounds the organs, which has decreased in size. Last beneficial effect of the loss of smell: the mice which presented an intolerance to glucose in addition to their obesity (risk factor for diabetes), also found a normal tolerance.
An alternative to bariatric surgery?
Despite all these encouraging aspects, several obstacles remain. First of all, these results were obtained in mice. It would be necessary to be able to attest them on the Man. Then, the loss of smell also has deleterious effects on the body: it increases the production of norepinephrine, a stress response hormone linked to the sympathetic nervous system. In doing so, it increases the risk of a heart attack.
According to the researchers, depriving all patients who want to lose a little weight of their sense of smell is not an option. On the other hand, this technique could constitute an alternative to bariatric surgery in the treatment of obesity. It would then be a question of suppressing the sense of smell for six months to reprogram the person’s metabolism, before letting the olfactory neurons rebuild themselves and then restore this sense in the patient.
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