Could eating a high-fat diet lead to reduced sense of smell? Researchers found mice that became obese through such a diet only had 50% of the brain cells responsible for encoding odor signals.
According to study leader Nicolas Thiebaud, a postdoctoral researcher at Florida State, this association "opens up a lot of possibilities for obesity research."
More than a third of US adults are obese, according to the Centers for Disease Control and Prevention (CDC). A lack of energy balance is the most common cause of obesity, determined by what we eat and drink.
But although many health implications of obesity are well established, the team notes that little is known on how the condition affects the body's sensory systems.
"Because olfaction (sense of smell) is linked with ingestive behavior to guide food choice, its potential dysfunction during obesity could evoke a positive feedback loop to perpetuate poor ingestive behaviors," they explain.
With this in mind, the team conducted a 6-month mouse study where they induced obesity in a group of mice by feeding them a high-fat diet every day. Acting as controls, another group of mice was fed standard chow. In addition, the researchers included mice in the study that were genetically obese. That is, they did not become obese through eating a diet high in fat.
During the study period, all mice were taught to associate a certain odor with a reward - water.
Mice fed high-fat diet had only 50% of brain cells that encode odor signals
The study findings, recently published in The Journal of Neuroscience, revealed that the mice fed the high-fat diet only had 50% of the neurons that work to encode odor signals in the brain.
Mice fed the high-fat diet were slower to make an association between the odor and reward, compared with those fed standard chow.
When the researchers attempted to teach mice a reward association with a new odor, those fed the high-fat diet were unable to adapt as quickly as the control mice - suggesting they had reduced sense of smell.
But the researchers say the most surprising finding was that when the mice fed the high-fat diet were moved to standard chow, leading to weight loss and normal blood chemistry, their reduced sense of smell remained.
"It was surprising to us that mice that were genetically obese were not perturbed in terms of anatomical loss but that those that consumed fat in the diet had anatomical and sensory behavioral losses," Nicolas Thiebaud and co-author Debra Fadool, of the Department of Biological Science and Program in Neuroscience and the Institute of Molecular Biophysics at Florida State, told Medical News Today.
Explaining why they believe a high-fat diet had this impact on sense of smell in the mice, Thiebaud and Fadool told us:
"Our findings show an increase in the cell death and microglial cell infiltration, suggesting that high-fat content diet leads to an increase in the inflammatory status of the olfactory mucosa that explains the diminution in olfactory sensory neurons.
However, we do not exclude that a high-fat diet also disturbs the function of other brain areas involved in processing the olfactory signals. Obesity also causes high levels of glucose and insulin, and we know that ion channels in the olfactory system act as sensors to these internal chemical cues. Obesity may disrupt the normal homeostatic sensors."
Fadool and Thiebaud said they do not know whether a similar association exists in humans. "There are numerous epidemiological factors that affect human health that complicate scientifically controlled experiments and that is why we utilize rodent models," they note.
"However, we would not be surprised if similar principles exist in humans. There are many similarities between the structure and molecular functioning of the olfactory system between the two species."
The researchers say that since they are part of a basic science laboratory, they do not plan to follow up these findings. But they note that there are many good clinical researchers within their professional society who are eager to do so.
It is not only sense of smell that could be affected by a high-fat diet. Last year, Medical News Today reported on a study by researchers from Michigan State University, claiming high-fat diets during puberty may increase the risk of breast cancer. Other research, published in the journal Psychoneuroendocrinology, linked high-fat diets to ADHD and learning problems.