Although the new study — now published in the journal PLOS Biology — was carried out in mice, the findings shed a clarifying light on a poorly understood phenomenon: the blunting of taste buds frequently noticed in people with obesity.
Eating delicious food activates reward centers in the brain. Dopamine — the "sex, drugs, and rock 'n' roll" neurotransmitter — is released every time our taste buds come into contact with yummy flavors.
Taste buds are nerve endings that comprise 50–100 different cells.
It's a fact that people with obesity tend to lose their sense of taste. However, until now, researchers had few clues as to how this happens, on a molecular level.
So, scientists at Cornell University in Ithaca, NY, led by Andrew Kaufman and Robin Dando, set out to explore the link between taste buds and obesity.
Obesity cuts down on taste buds
For 8 weeks, Kaufman and team fed rodents either a regular diet (consisting of only 14 percent fat) or a high-fat diet (which consisted of 58 percent fat).
After the study period, obese mice had fewer taste buds than the regular mice. In fact, the high-fat diet reduced the number of their taste buds by 25 percent. But why did this happen?
The researchers also found that obese mice had higher levels of a pro-inflammatory cell called TNF-alpha, a class of pro-inflammatory cytokine.
Kaufman and team also genetically engineered a mouse model that was incapable of producing these cytokines, and interestingly, the researchers found that these mice did not lose any taste buds — despite being fed a high-fat diet and becoming obese.
Additionally, the scientists injected TNF-alpha into the tongues of normal-weight mice. This caused the rodents to lose taste buds as well, despite the fact that they were not obese.
Obesity-induced inflammation is key
Research has shown that obesity increases inflammation — which often leads to cardiometabolic disorders — and this new study furthers the theory that the same inflammation is responsible for the reduced number of taste buds.
These findings "demonstrate that chronic low-grade inflammation brought on by obesity [...] is likely the cause of taste dysfunction seen in obese populations — by upsetting this balance of renewal and cell death," write the authors.
In fact, the researchers noted that obese mice had a higher rate of taste bud cell death, while the rate at which new progenitor cells appeared in the tongue decreased.
"These data together suggest that gross adiposity stemming from chronic exposure to a high-fat diet is associated with a low-grade inflammatory response causing a disruption in the balancing mechanisms of taste bud maintenance and renewal."
"These results may point to novel therapeutic strategies for alleviating taste dysfunction in obese populations."