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Pathway Scientist Discovers Links between Sense of Smell and Body Weight

American Diabetes Association  | Published on 7/1/2019

The brain is responsible for sensing, coordinating, and responding to all sorts of cues in our bodies and our environments. We have long appreciated the role that the sense of smell plays in our selection and enjoyment of food. However, a new study shows that, at least in mice, the sense of smell is actually linked to how the body controls energy balance, influencing both obesity and insulin resistance—key risk factors for type 2 diabetes.

The American Diabetes Association awarded one of its highly-competitive Pathway to Stop Diabetes® grants to Celine Riera, PhD, in 2015 to investigate these links. Dr. Riera recently transitioned from her position as a postdoctoral fellow at the University of California, Berkeley, to her first independent faculty position at Cedars-Sinai Medical Center in Los Angeles.

In a paper published in the prestigious journal Cell Metabolism, Dr. Riera and colleagues described exciting data indicating that when the sense of smell is destroyed, mice lose weight and improve their sensitivity to insulin. Surprisingly, this weight loss was not connected to how much the mice ate—or even how much they exercised. Instead, animals in both groups ate the same amount and moved the same amount. Yet, those who were unable to smell burned more calories and weighed less than those whose sense of smell remained intact.

To further investigate this link, the researchers tried the opposite experiment. They generated “super-smeller” mice with a sharper sense of smell than normal. Again, the super-smellers consumed the same amount of food as the normal mice, but they became obese. These results reinforced the idea that the sense of smell affects how the body determines whether to burn energy or to store it as fat.

Interestingly, the investigators found that when the sense of smell is altered, a host of hormone levels change. For example, when the sense of smell is blunted, adrenaline levels rise, stimulating the metabolism of fat. The changes in hormone levels in the smell-deficient mice coordinate to protect the animals from the effects of a high-fat diet.

It remains to be determined whether the same links between smell and metabolism exist in humans. There are cases when people have lost the sense of smell and have experienced reduced appetite. However, the mouse studies are indicating a totally different connection between these systems—one not linked to a change in food consumption. Humans naturally experience an enhancement in their sense of small after fasting. It may be that smell sensation is activated when energy stores are running low—and helps coordinate the body’s food intake and metabolism.

By better understanding these links in humans, we may be able to develop new therapies that can prevent obesity and insulin resistance. 

This fascinating work is receiving a great deal of attention and has been featured by several news outlets, including the Los Angeles Times, Science, The Scientist, Esquire, SF Gate, and CBS News.

 

Riera CE, Tsaousidou E, Halloran J, Follett P, Hahn O, Pereira MMA, Ruud LE, Alber J, Tharp K, Anderson CM, Bronneke H, Hampel B, Filho CD, Stahl SA, Bruning JC, Dillin A. The Sense of Smell Impacts Metabolic Health and Obesity. Cell Metabolism. 26: 198-211.