Experiments at the University of California, Berkeley, published in the journal Cell Metabolism, finds that obese mice that lost their sense of smell also lost weight, and mice that had a bad sense of smell and ate the same amount of fatty food as mice that retained their sense of smell doubled to twice their normal weight.
Super-smellers – mice with a boosted sense of smell – got even fatter on a high-fat diet than did mice with a normal sense of smell.
The research finds that the smell-deficient mice rapidly burned calories by up-regulating their sympathetic nervous system, which is known to increase fat burning. The mice turned their beige fat cells – the fat storage cells that accumulate around our thighs and midriffs – into brown fat cells, which burn fatty acids to produce heat. Some turned almost all of their beige fat into brown fat, becoming lean, mean burning machines.
So what does all this mean for us? Topline is that the aroma of what we eat may play an important role in how the body deals with calories. If you can’t smell your food, you may burn it rather than store it.
“This paper is one of the first studies that really shows if we manipulate olfactory inputs, we can actually alter how the brain perceives energy balance, and how the brain regulates energy balance,” says Céline Riera, a former UC Berkeley postdoctoral fellow now at Cedars-Sinai Medical Center, in Los Angeles.
She goes on to say that humans who lose their sense of smell because of age, injury or diseases such as Parkinson’s often become anorexic, but the cause – till now – has been unclear because loss of pleasure in eating also leads to depression, which itself can cause loss of appetite.
“Weight gain isn’t purely a measure of the calories taken in; it’s also related to how those calories are perceived,” says senior author Andrew Dillin, the Thomas and Stacey Siebel Distinguished Chair in Stem Cell Research, a professor of molecular and cell biology, and a Howard Hughes Medical Institute investigator.
Riera also notes that mice and humans are more sensitive to smells when they are hungry than after they’ve eaten; their research is looking to see whether the lack of smell tricks the body into thinking it has already eaten. If so, this could be a huge advance in treating obesity, as there are drugs that can temporarily eliminate or decrease the sense of smell.
Before you think this is the greatest advance possible, the researchers found that the loss of smell was accompanied by a large increase in levels of the hormone noradrenaline, which is a stress response tied to the sympathetic nervous system. In humans, such a sustained rise in this hormone could lead to a heart attack.
Another reason to just eat less and exercise more.