Our sense of smell has been linked to taste for quite some time.
But new research, published on July 5 in Cell Metabolism, has found that if you can’t smell what you eat, you may not put on as much weight.
Not because you’re eating less, mind you.
The experiment was performed on two groups of mice – one that could smell, and one whose sense of smell was temporarily lost.
Both groups were fed high-fat food and both ate the same amount.
While the normal mice gained 100 per cent of their normal weight, the smell-deficient mice only gained, at most, 10 percent more weight.
“I was shocked — the effect was so robust,” said senior author, UC Berkeley stem cell biologist and geneticist Professor Andrew Dillin.
“I was convinced they were just eating less. When it became clear they weren’t, I thought, ‘Wow, this is incredibly interesting’.”
He explains that weight gain isn’t just a measure of calories taken in, it also relates to how those calories are perceived.
These results point to a connection between the system that controls smell (olfactory system) and parts of the brain that control metabolism.
Study author Céline Riera says this is one of the first studies that really show that if we manipulate olfactory (sense of smell) inputs, we can alter how the brain perceives and regulates energy balance.
When it comes to food, she says our sense of smell depends on our hunger levels.
When we’re hungry, food smells more appealing. So if we come across food at that point, our body stores that intake as calories.
But if we encounter food but don’t smell it, the lack of smell “tricks” the body into thinking it’s already eaten.
If the body thinks it has already stored adequate calories, it feels it can then burn the rest.
That’s what happened to the mice in this experiment.
The smell-deficient mice burned calories by up-regulating their sympathetic nervous system to burn more fat.
They turned their beige fat cells (stored as fat) into brown fat cells, which burn fatty acids to make heat.
Their white fat cells (those that cling to internal organs) also shrank, yet there was no effect on their muscles, bones or other organs.
“The mice with no sense of smell had turned on a program to burn fat,” says Professor Dillin.
While the study seems promising, obesity expert Dr Georgia Rigas from the RACGP has her reservations.
She notes the study duration was short, lasting for three weeks.
Once the sense of smell was returned to the smell-deficient mice, she believes they would have simply gained weight.
She also worries about translating rodent research to humans, noting particularly that we have different types of fat cells than mice.
However, she believes this research has provided a working hypothesis upon which to design future studies.
But sacrificing your sense of smell seems like a drastic step to take in order to keep your waistline in check.
Mind you, Professor Dillin says it could be a viable alternative for people contemplating surgery for obesity.
“For that small group of people, 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.”
(For now, Dr Rigas says bariatric surgery is the only proven and safe therapy known to assist patients with Class III obesity.)
In case you’re wondering, temporary measures to block your nose won’t cut it, says Professor Dillin, as our mouths also admit olfactory information.
A simple way to use this knowledge to our advantage is to fill up on good, healthy food before encountering tempting situations, says Dr Rigas.
In other words, have lunch before going to the bakery, so those flaky croissants don’t entice you when you’re at your most sensitive.
Professor Dillin hopes this research may help create a drug that blocks the same metabolic circuitry of the olfactory system, without affecting one’s sense of smell.
If it could be achieved, he says, “That would be amazing.”