Simply Smelling Food Can Cause Weight Gain

Smell is a large part of the appeal of food. If one's sense of smell were removed, he would likely lose weight. This statement was recently proven true by researchers at the University of California, Berkeley who performed experiments on mice lacking the ability to smell. Such mice lost weight. However, the odd part of this study is that mice who could not smell properly consumed the same amount of fatty food as those who had a normal sense of smell.   

About the Results

Mice with a regular sense of smell increased to two times their typical weight after consuming the same amount of fatty food as mice lacking in smell. Furthermore, mice with a heightened sense of smell fattened up much more than mice with an average ability to smell. The findings show that the odor of foods one consumes plays a powerful role in how the body handles the calories. This means if one can't smell his food, there is a good chance his body will burn it instead of store it.

There is clearly a strong connection between the smell system and portions of the brain that control metabolism. Specifically, the hypothalamus is essential. Yet the exact neural circuits responsible for this phenomenon are still unknown. The manipulation of olfactory inputs really does change the way in which the brain perceives energy balance as well as how the brain controls energy balance.

People who lose their sense of smell due to a disease like Parkinson’s, injury or age sometimes become anorexic. Yet the cause is not clearly defined as the loss of pleasure from consuming food commonly leads to depression that can spur the loss of appetite in itself. The study implies interventions might be helpful for those who lose their sense of smell and overweight individuals. It is clear that weight gain is not completely dictated by the number of calories consumed. Sensory systems are also important to the role the metabolism plays. The manner in which the calories are received is also important. 

Hunger, Calories, and Smell 

Mice and humans are more sensitive to odors when hungry than following consuming food. It is possible the lack of smell fools the body into believing it has already consumed food. The body stores calories when searching out food just in case no food can be procured. Once food is acquired, the body burns those stored calories.

Blocking the Sense of Smell

The researchers used a couple different techniques to block adult mice's sense of smell. They genetically engineered mice in order to express the diphtheria receptor within the olfactory neurons that reach all the way from the odor receptors in the nose to the brain's olfactory center. A diphtheria toxin was applied to the nose. Neurons died and the mice were subsequently deprived of their ability to smell until stem cells were applied for regeneration. The scientists also created a benign virus to send the receptor to olfactory cells through inhalation. The diphtheria toxin eliminated the sense of smell for nearly a full month.

What's Next? 

If the study performed on mice is validated in humans, it might be possible to create a drug that does not conflict with smell yet still blocks metabolic pathways. Eliminating the ability to smell in those who desire to lose weight is possible yet few would take this route. Those who are morbidly obese and considering an extreme measure like bariatric surgery might consider such a step. Perhaps eliminating one's sense of smell for half a year and allowing the olfactory neurons to grow back would rewire the patient's metabolic circuitry.