NEW TREATMENTS
July 14, 2017

Obesity and Our Sense of Smell

A study in mice finds those with an enhanced sense of smell gained more weight; those with no sense of smell lost it. A new diet strategy?

The smell of food is intricately intertwined with how it tastes. So it’s not surprising that new research suggests that a loss of the sense of smell results in weight loss. But the reason why may be more complicated than you think.

Researchers at the University of California, Berkeley temporarily blocked the sense of smell in one set of laboratory mice, left it alone in another, and enhanced the sense of smell in a third group. Obese mice that were smell-deprived ate the same amount of fatty food as mice that could smell, yet lost weight, specifically fat mass. Those who retained their sense of smell doubled their weight, and those mice whose sense of smell was enhanced gained even more weight than those whose sense of smell was not blocked.

What’s going on here?

“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.”

People often become anorexic when they can no longer smell. Diseases such as Parkinson’s, cigarette smoking, certain types of injuries or age can rob a person of their ability to smell. It’s been assumed that poor appetite and weight loss were due to the loss of smell which takes away much of the pleasure of eating. That in itself can lead to depression, which can itself cause a loss of appetite.

The findings from this research bring up new possibilities. Does the sense of smell play a role in how the body handles calories? If you can’t smell what you’re eating, your body might prefer to burn the calories rather than store them. Perhaps there is a connection between the olfactory (smell) system and parts of the brain that regulate metabolism via circuits in the brain that have not been discovered.

Hunger makes both mice and human beings more sensitive to smells, so maybe not being able to smell tricks the body into believing it’s already been fed and causes calories to be stored while it’s waiting to be fed. Perhaps once a person has eaten, the body feels free to burn the calories, according to researcher Céline Riera.

Would eliminating smell in humans be a viable method of weight loss? It would be pretty drastic, said Andrew Dillin, PhD, professor of genetics, genomics and development at the UC Berkeley and senior author of the study, but it might be an alternative to stomach stapling or bariatric surgery for morbidly obese individuals.

“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 Dillin, in a statement. “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.”

Keep in mind, this was an animal study and results from animal studies don’t always turn out the same way in human studies. However, this new knowledge could lead to future treatments for obesity.

The study is published in Cell Metabolism.

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