The research team have determined that the signally between smell and the sympathetic nervous system flows through the hypothalamus.
According to The Daily Mail, they fed the two groups of mice the exact same high-fat diet, but the mice with no smell lost 16 percent of their body weight while the other mice gained weight. But if a recent research is to go by, sense of smell that helps in enjoying the food may be inadvertently making you fat.
Even when the super-smellers were exposed to "social" smells, such as the scent of other mice of the opposite sex, they were shown to be at a greater risk to gain more weight and suffer an impairment of their metabolism compared to normal or smell-deficient mice.
Experiments conducted at the University of California, Berkeley, suggest that the odor of food has a direct link with how the body processes the calories. The body stores calories when it is unsuccessful in searching for food, and feels free to burn it when food is secured.
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.
To find out how smelling food can affect weight gain, the researchers studied obese mice with an altered sense of smell.
"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", said Céline Riera, a former UC Berkeley postdoctoral fellow now at Cedars-Sinai Medical Center in Los Angeles.
The smell-deficient mice rapidly burned calories by up- regulating their sympathetic nervous system, which is known to increase fat burning. But while the smell-deficient mice gained at most 10 percent more weight, going from 25-30 grams to 33 grams, the normal mice gained about 100 percent of their normal weight, ballooning up to 60 grams.
Because the fat-burning program is off by default, it isn't clear how an enhanced sense of smell is linked to weight gain. The team, headed by molecular biologist Andrew Dillin, gave the mice regular doses of the diphtheria toxin, which puts a temporary halt on odor-sensing neurons.
The obese mice with glucose bigotry (a status that brings on diabetes) not only lost weight in spite of a high fat diet but also achieved normal glucose tolerance. Some turned nearly all of their beige fat into brown fat, becoming lean, mean burning machines. These mice had highly sensitive noses. Also, super-smeller mice (mice with boosted sense of smell) got fatter than mice with a normal sense of smell when provided with a high-fat diet.
The senses of smell and taste become heightened in anticipation of a meal. Also, their bone mass, organs, or muscles were left unaffected.
The results of the new study were published in the journal Cell Metabolism, and the findings point to an unexplored link between olfactory neurons and weight gain.