Nav: Home

Mice lacking a sense of smell stay thin

July 05, 2017

Mice engineered to lack a sense of smell lose weight on a high-fat diet, researchers report July 5th in the journal Cell Metabolism. The mice ate just as much as counterparts with unaltered senses, yet lost an average of about 16 percent of their body weight. The weight loss was almost entirely from fat. In addition, mice with an enhanced sense of smell gain more weight than mice with typical olfactory abilities despite similar diets.

"It's one of the most interesting discoveries to come out of my lab," says principle investigator Andrew Dillin, professor of molecular and cell biology at the University of California, Berkeley. "What's happening to those calories?"

Dillin and his team initially suspected that mice without the ability to smell ate less. But when they measured food intake, the mice ate just as much as the control group. They also ruled out differences in nutrient absorption and excretion. "Weight gain isn't purely a measure of the calories taken in. It's also related to how those calories are perceived," says Dillin.

He had expected the loss of smell to have some effect on feeding. The senses of smell and taste become heightened in anticipation of a meal. After feeding, the senses are dramatically reduced. "There is a known link between food intake and sense of smell," says Dillin.

But the change in weight after the loss of smell was visibly noticeable. For instance, two mice fed the same high-fat diet both became obese. After Dillin's team eliminated the sense of smell in one of those mice, its weight dropped by about a third, to 33 grams. The other mouse maintained a weight of 49 grams. "I never expected turning off smell would have such dramatic weight-loss effects," says Dillin.

Because the weight change was so substantial, Dillin and colleagues created a second mouse model lacking a sense of smell. The first mouse model was engineered to lose its olfactory sensory neurons, the cells that detect odors and relay the information into the brain, when given a certain drug. Dillin worried that the process killed more than just olfactory sensory neurons. In the second mouse model, his team ablated olfactory sensory neurons using an inhaled virus, producing a similar loss of olfactory sensory neurons with a lower chance of affecting cells outside the olfactory system.

The results remained the essentially the same, with slightly less weight loss in the second mouse model.

Since most of the weight lost was fat, Dillin's team zoomed in on changes in fat deposits in the animals. They found that brown fat deposits were actively burning. In addition, the body's other form of fat, white fat, was transforming into brown fat and burning. "The mice with no sense of smell had turned on a program to burn fat," says Dillin.

The team also found high levels of adrenaline in the blood of these animals. The team traced this signal back to the sympathetic nervous system, which under normal circumstances governs the fight-or-flight response as well as responses to extremes, such as cold. Under these stressful conditions, the body energizes itself by triggering a release of catecholamines, or adrenaline, "which is known to turn on this brown-fat-burning program," says Dillin.

The team has not yet determined the link between the olfactory sensory neurons and the sympathetic nervous system, but they believe the signaling flows through the hypothalamus. First author Celine Riera, a post-doctoral fellow in Dillin's lab, plans to tease out this neural signaling pathway in her future research.

Whether or not humans respond similarly to loss of smell is unknown.

In casual conversation, Dillin shared his results with colleague Jens Brüning, Director of the Max Planck Institute for Metabolism Research. It turned out that Brüning had created a super-smelling mouse. "It has the opposite phenotype," says Brüning.

Brüning's super-smeller mice eat just as much as their control counterparts, but gain even more weight, predominantly body fat. Because the fat-burning program is off by default, it isn't clear how an enhanced sense of smell is linked to weight gain.
This work was supported by the Howard Hughes Medical Institute, the Glenn Center for Research on Aging, and the American Diabetes Association.

Cell Metabolism, Riera et al.: "The sense of smell impacts metabolic health and obesity."

Cell Metabolism (@Cell_Metabolism), published by Cell Press, is a monthly journal that publishes reports of novel results in metabolic biology, from molecular and cellular biology to translational studies. The journal aims to highlight work addressing the molecular mechanisms underlying physiology and homeostasis in health and disease. Visit: To receive Cell Press media alerts, contact

Cell Press

Related Weight Loss Articles:

Changing weight-loss strategies, attempts
The proportion of adults who tried to lose weight in the previous year increased from 1999 to 2016 but the findings of this observational study suggest the results may have been unsatisfactory.
Quality of life changes after weight loss
Obesity increases a number of adverse health consequences including reduced health-related quality of life.
Weight loss medicines underutilized by veterans
Despite the availability of new weight management medications and several clinical guidelines recommending their use as part of a comprehensive treatment plan for obesity, a new study has found that their use is extremely low (about one percent) among eligible Veterans.
Is the most effective weight-loss strategy really that hard?
Dietary self-monitoring is the best predictor of weight-loss success. But the practice is viewed as so unpleasant and time-consuming, many would-be weight-losers won't adopt it.
Study: Faster weight loss no better than slow weight loss for health benefits
Losing weight slowly or quickly won't tip the scale in your favor when it comes to overall health, according to new research.
Mindfulness training may help support weight loss
Mindfulness training may improve the effectiveness of intensive weight management programs, according to a small study published in the Endocrine Society's Journal of Clinical Endocrinology & Metabolism.
Does weight loss before surgery provide benefits?
For obese and overweight patients, it is common for various surgical procedures to be deferred until they have lost weight through diet and exercise.
Can community exercise prevent bone loss from weight loss in older adults?
In a Journal of Bone and Mineral Research study of older adults with obesity who were cutting calories, an intervention that incorporated resistance training, aerobic training, or neither did not prevent bone loss associated with active weight loss.
Daily fasting works for weight loss
A new study shows that daily fasting is an effective tool to reduce weight and lower blood pressure.
Weight loss is an important predictor of cancer
Unintended weight loss is the second highest risk factor for some forms of cancer, concludes the first robust research analysis to examine the association.
More Weight Loss News and Weight Loss Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Climate Mindset
In the past few months, human beings have come together to fight a global threat. This hour, TED speakers explore how our response can be the catalyst to fight another global crisis: climate change. Guests include political strategist Tom Rivett-Carnac, diplomat Christiana Figueres, climate justice activist Xiye Bastida, and writer, illustrator, and artist Oliver Jeffers.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Speedy Beet
There are few musical moments more well-worn than the first four notes of Beethoven's Fifth Symphony. But in this short, we find out that Beethoven might have made a last-ditch effort to keep his music from ever feeling familiar, to keep pushing his listeners to a kind of psychological limit. Big thanks to our Brooklyn Philharmonic musicians: Deborah Buck and Suzy Perelman on violin, Arash Amini on cello, and Ah Ling Neu on viola. And check out The First Four Notes, Matthew Guerrieri's book on Beethoven's Fifth. Support Radiolab today at