Smelling Your Food First Can Make You Fat: UC Berkeley Study
You may not realize it but your sense of smell may influence just how much weight you gain when you eat food.
A new study by the University of California Berkeley suggests that the odor of the food that people eat may play a key role in how the body is able to deal with calories. Findings show that if individuals won't be able to smell their food, it is likely that their bodies would burn it instead of storing it.
To find out how smelling food can affect weight gain, the researchers studied obese mice with an altered sense of smell.
Some of the animals were temporarily stripped of their ability to smell by having their olfactory neurons in their noses destroyed through gene therapy. However, the researchers left some stem cells intact to let the neurons grow back after a few weeks.
The team also had the sense of smell of other mice be heightened than normal. These "super-smellers" were used to show how having a more acute smell system would affect the amount of food that individuals eat.
Both groups of mice were given the same amount of food throughout the duration of the experiment. Their development was then compared to those of mice with a regular sense of smell.
Impact Of Sense Of Smell On Weight Gain
The researchers discovered that the smell-deficient obese mice lost weight even when they consumed the same amount of food as those with the normal sense of smell. They saw that these animals burned fat faster by up-regulating their sympathetic nervous system.
The team also found that these obese mice, which had developed glucose intolerance, managed to bring their tolerance levels to normal even though they consumed a high-fat diet.
Despite these seemingly positive gains, the smell-deficient animals also suffered negative effects, particularly an increased level of noradrenaline hormones in their bodies. This is believed to be a stress response associated with the sympathetic nervous system. If a person were to have such high levels of the hormone, he or she is likely to suffer a heart attack.
Meanwhile, the obese mice that had heightened sense of smell became fatter, ballooning to twice their regular weight. This is even though they consumed the same amount of food as normal mice and their smell-deficient counterparts.
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.
The results show an important relationship between the olfactory system and the parts of the brain known to control metabolism such as the hypothalamus. However, scientists have yet to identify the exact neural circuits that connect the two systems.
The researchers believe that their study is the first of its kind to demonstrate the possibility of manipulating the smell system to affect how our brains perceive and regulate energy balance.
The team hopes that the findings would eventually lead to new ways to help people who lost their sense of smell and those who are having troubles losing weight.
"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," Andrew Dillin, a senior author of the study, explained.
"If we can validate this in humans, perhaps we can actually make a drug that doesn't interfere with smell but still blocks that metabolic circuitry. That would be amazing."
The findings of the UC Berkeley study are featured in the journal Cell Metabolism.