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A new study by Cell Metabolism revealed that weight gain can also be caused by a person’s sense of smell.
Obesity is one of the increasing problems of the society today. By 2010, about two in three Americans are obese or overweight, and these include children. There are some people who blame this problem on having a desk job, others blame it on a person’s eating habits, some on a person’s lifestyle, and on many other things. A new study by Cell Metabolism revealed that weight gain can also be caused by a person’s sense of smell.
The team of researchers who made these surprising findings said that the mice which sense of smell they temporarily disabled retained its normal weight despite feeding on a high-fat diet. On the other hand, the other mice which sense of smell they boosted gained significant weight despite it feeding on the same high-fat diet.
“Sensory systems play a role in metabolism. Weight gain isn’t purely a measure of the calories taken in; it’s also related to how those calories are perceived,” said senior author Andrew Dillin, the Thomas and Stacey Siebel Distinguished Chair in Stem Cell Research and professor of molecular and cell biology and Howard Hughes Medical Institute Investigator.
A new method to lose weight?
The results of the study suggest a connection between the olfactory system and the part of the brain that control metabolism, the hypothalamus. It suggests people who are obese or overweight can lose weight once they lose their sense of smell no matter how fatty or how much they eat.
Céline Riera is a former UC Berkeley postdoctoral fellow who is now at the Cedars-Sinai Medical Center in Los Angeles. According to Riera, humans, like mice, are very sensitive to smells when they are hungry. She says the results of this study may also suggest that the lack of smell could be a way to trick the body into believing it has already eaten. The body is structured to store calories until the search for food is successful, the point wherein the body will start burning calories again.
“This paper is one of the first studies that really shows if we manipulate olfactory inputs we can actually alter how the brain perceives energy balance, and how the brain regulates energy balance,” she said.
Some people lose their sense of smell due to injury, a disease, or their age. With these conclusions and analyses, researchers believe that the lack of smell could actually benefit obese and overweight people. They also presume that this study could shed light to the discovery of a new remedy toward resolving the increasing number of overweight and obese people.
“If we can validate this in humans, perhaps we can actually make a drug that doesn’t interfere with smell but still blocks that metabolic circuitry. That would be amazing.” Dillin said.
For this study, the researchers deactivated the sense of smell of one group of mice by the use of gene therapy which destroyed its olfactory neurons in its noses. This method did not hurt the spare stem cells, which allowed the olfactory neurons to regrow after some three weeks.
They observed that the mice that lack the sense of smell managed to burn more calories by up-regulating their sympathetic nervous system, which is known to up fat burning. According to the researchers, some of the mice had their beige fat cells turned into brown fat cells, which burn fatty acids to produce heat, while others had almost all of their beige fat into brown fat, making their body burn fat rapidly. This group of mice had their white fat cells, which are often linked to poor health outcomes, significantly reduced, while those obese mice that are glucose-intolerant regained glucose tolerance.
However, there are side effects to the loss of smell. These include a significant increase in noradrenaline, a hormone related to stress response. For humans, this could lead to a heart attack.
Also, they noted that the obese mice that lost weight after their sense of smell were disabled lost only fat weight. This method of weight loss did not have an effect on their muscle, bone mass, or organs.
Dillin believes this method would benefit many extremely obese people despite the risk of increased levels of noradrenaline, especially if they are considering surgery to fix their weight problem.
“You could wipe out their smell for maybe six months and then let the olfactory neurons grow back after they’ve got their metabolic program rewired,” he said.
The researchers teamed up with German researchers who made the findings that a group of mice, which had their sense of smell boosted, gained weight drastically. With such revelation, they came up with a similar conclusion and believe these studies will not only provide information to help better understand how weight loss occurs, but also understand better how eating disorders can be developed.
“We think olfactory neurons are very important for controlling pleasure of food and if we have a way to modulate this pathway, we might be able to block cravings in these people and help them with managing their food intake.” Riera said.