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Sense of Smell Equals Weight Loss
2019-01-07 15:58:46
Khristian Maclang

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Photo by: Jastrow / Wikimedia Commons

Study shows that food aroma plays a vital role on how the brain perceives calories.In the new study, researchers from the University of California, Berkeley, found that weight gain is not only involved in the intake of calories but also how the body makes out these calories.

Results from the study were inevitable considering that food aroma is key to the enjoyment of food.People tend to get an appetite for something that smells really good.

Researchers experimented on overweight mice and found that mice who lost the ability to get a whiff of food aroma instantly lost weight even after eating a ton of fatty foods similar to those with a boosted sense of smell.They also decreased in size compared to mice that maintained their normal sense of smell.

Destroying Olfactory Neurons

Researchers zapped olfactory neurons present in the noses of adult mice to lose their sense of smell.  However, they spared stem cells to enable the mice to regain their smelling abilities after a few weeks.

During the study, researchers developed two methods to block smell temporarily in adult mice.For the first mice, they used gene therapy to initiate a diphtheria receptor in their olfactory neurons.On spraying diphtheria through their nose, olfactory neurons died making the mice smell-deficient.

For the second group, the researchers genetically engineered a benign virus to carry a diphtheria receptor into the mice’ noses through inhalation.On spraying the diphtheria toxin, the mice also became smell deficient for three weeks.

On losing their sense of smell, the mice increased their response to stimuli in their sympathetic nervous system, thus burnt calories instantly.Consequently, they were able to convert beige fat cells to brown fat cells which burn fatty acids for heat production.More so, some of the mice converted almost all of their beige fat to brown fat, thus becoming very thin.  

The mice in both experiments were given a high-fat diet similar to mice with a normal sense of smell.However, they only had a 10% increase in their weight while mice with normal smell ability gained weight by 100%.

Obese mice that had become glucose intolerant- a causative of diabetes lost weight and recovered their normal glucose tolerance, though the destruction of olfactory neurons also caused a massive increase of noradrenaline hormone-a stress response.In human beings, a significant increase in the noradrenaline like this can cause a heart attack.


The findings show that smelling food is a vital piece in a larger metabolic process that determines how calories are dealt with by the body.Per say, if you lack the ability to smell nice aromas, your body chooses to burn the food to produce heat rather than store it.The results show a connection between the olfactory and hypothalamus- a part of the brain that controls metabolic processes.Scientists have not yet determined the connecting neural circuits.

One of the researchers, Céline Riera of Cedars-Sinai Medical Center Los Angeles says, “This paper is one of the first studies that really show if we manipulate olfactory inputs we can actually alter how the brain perceives energy balance, and how the brain regulates energy balance.”

The new study has opened doors for future research on the causes of appetite loss for people who become smell deficient due to factors like old age, diseases like Parkinson’s or even from injuries.Prior research only shows that these patients lose their appetite and become anorexic.Results from the study also suggest that interventions for people who lost their sense of smell, as well as those who seek to lose weight, are possible.

Senior author of the study, Andrew Dillin says "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.”

The research team proposes that if the concept is validated on humans, a drug that blocks the metabolic circuitry, and not tampers with the sense of smell can be made.The study points out that both mice and humans show high sensitivity to smell when hungry as compared to when they are full.For this reason, lack of smell probably tricks the body to burn calories, instead of storing it.

Helping the Morbidly Obese

Dillin noted that although eliminating the sense of smell in humans who wish to cut off unwanted fats is an extreme step, the process would be a practical alternative to bariatric surgeries and stomach stapling for morbidly obese fellows.He adds that olfactory could be wiped out in this group of people for about six months, then regrown back after they shed off a significant amount of fat.

The findings show that zapping olfactory neurons in people with eating disorders will help regulate the amount of food that they eat.This is because food cravings arise from food aromas, therefore blocking smell will consequently block cravings.

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