Does obesity reshape our sense of taste?

Obesity may alter the way we taste at the most fundamental level: by changing how our tongues react to different foods.

In a Nov. 13 study in the journal PLOS ONE, University at Buffalo biologists report that being severely overweight impaired the ability of mice to detect sweets.

Compared with slimmer counterparts, the plump mice had fewer taste cells that responded to sweet stimuli. What’s more, the cells that did respond to sweetness reacted relatively weakly.

The findings peel back a new layer of the mystery of how obesity alters our relationship to food.

“Studies have shown that obesity can lead to alterations in the brain, as well as the nerves that control the peripheral taste system, but no one had ever looked at the cells on the tongue that make contact with food,” said lead scientist Kathryn Medler, PhD, UB associate professor of biological sciences.

“What we see is that even at this level — at the first step in the taste pathway — the taste receptor cells themselves are affected by obesity,” Medler said. “The obese mice have fewer taste cells that respond to sweet stimuli, and they don’t respond as well.”

The research matters because taste plays an important role in regulating appetite: what we eat, and how much we consume.

How an inability to detect sweetness might encourage weight gain is unclear, but past research has shown that obese people yearn for sweet and savory foods though they may not taste these flavors as well as thinner people.

Medler said it’s possible that trouble detecting sweetness may lead obese mice to eat more than their leaner counterparts to get the same payoff.

Learning more about the connection between taste, appetite and obesity is important, she said, because it could lead to new methods for encouraging healthy eating.

“If we understand how these taste cells are affected and how we can get these cells back to normal, it could lead to new treatments,” Medler said. “These cells are out on your tongue and are more accessible than cells in other parts of your body, like your brain.”

The new PLOS ONE study compared 25 normal mice to 25 of their littermates who were fed a high-fat diet and became obese.

To measure the animals’ response to different tastes, the research team looked at a process called calcium signaling. When cells “recognize” a certain taste, there is a temporary increase in the calcium levels inside the cells, and the scientists measured this change.

The results: Taste cells from the obese mice responded more weakly not only to sweetness but, surprisingly, to bitterness as well. Taste cells from both groups of animals reacted similarly to umami, a flavor associated with savory and meaty foods.

Scientists Discover How Animals Taste, and Avoid, High Salt Concentrations

For consumers of the typical Western diet—laden with levels of salt detrimental to long-term health—it may be hard to believe that there is such a thing as an innate aversion to very high concentrations of salt.

But Charles Zuker, PhD, and colleagues at Columbia University Medical Center have discovered how the tongue detects high concentrations of salt (think seawater levels, not potato chips), the first step in a salt-avoiding behavior common to most mammals.

The findings, which were published online in the journal Nature, could serve as a springboard for the development of taste modulators to help control the appetite for a high-salt diet and reduce the ill effects of too much sodium.

The sensation of saltiness is unique among the five basic tastes. Whereas mammals are always attracted to the tastes of sweet and umami, and repelled by sour and bitter, their behavioral response to salt dramatically changes with concentration.

“Salt taste in mammals can trigger two opposing behaviors,” said Dr. Zuker, professor in the Departments of Biochemistry & Molecular Biophysics and of Neuroscience at Columbia University College of Physicians & Surgeons. “Mammals are attracted to low concentrations of salt; they will choose a salty solution over a salt-free one. But they will reject highly concentrated salt solutions, even when salt-deprived.”

Over the past 15 years, the receptors and other cells on the tongue responsible for detecting sweet, sour, bitter, and umami tastes—as well as low concentrations of salt—have been uncovered largely through the efforts of Dr. Zuker and his collaborator Nicholas Ryba from the National Institute of Dental and Craniofacial Research.

“But we didn’t understand what was behind the aversion to high concentrations of salt,” said Yuki Oka, a postdoctoral fellow in Dr. Zuker’s laboratory and the lead author of the study.

The researchers expected high-salt receptors to reside in cells committed only to detecting high salt. “Over the years our studies have shown that each taste quality—sweet, bitter, sour, umami, and low-salt—is mediated by different cells,” Dr. Ryba said. “So we thought there must be different taste receptor cells for high-salt. But unexpectedly, Dr. Oka found high salt is mediated by cells we already knew.”