The Current Biology journal published the findings.
Three-quarters of supermarket foods, according to University of Michigan researcher Monica Dus, have added sugar, which makes her worry if our sense of taste can become numb to sweetness.
Now, a team of U-M researchers found that, indeed, a diet high in sugar did reduce the taste system’s capacity to detect sweetness in rats. Dus was interested in learning more about whether this phenomena was a physiological reaction the high-sugar diet was having on the senses of the rats.
Researchers from the University of Michigan, including Robert Bradley, Charlotte Mistretta, and Carrie Ferrario, discovered that rats on a high-sugar diet had a nearly 50% reduction in the responsiveness of the nerve that carries information about sweetness from the tongue to the brain.
A research conducted a lot of years ago revealed that people’s perceptions of sugar increased when their diets contained less of it. But how is that taking place? In a number of earlier studies, discovered that sugar reduces the receptivity of the nerve and reprograms the taste cells in fruit flies, but flies are still just flies.
“I really wanted to understand if and how it was happening in mammals.” said Monica Dus, Associate Professor of Molecular, Cellular, and Developmental.
Professors Bradley and Mistretta of the University of Michigan School of Dentistry, who have researched how taste works and how it is affected by food and illness, were contacted by Dus. Ferrario, an associate professor of pharmacology at the University of Michigan Medical School who specialises in the neuroscience of rat ingestive behaviour, was also contacted by the team. One set of rats received their usual meal from the researchers along with access to sugar water. Rats in the control group had access to ordinary water and their regular diet. The responses of the nerve as the tongue was stimulated with various solutions were recorded by the researchers using electrodes after four weeks. The front of the rat’s tongue, which is home to taste buds cells that detect chemicals, sends taste information to the brain via this nerve.
The rats were then given liquids with sweet, bitter, sour, salty, and umami flavours, and the researchers observed how the rodents reacted to touch and cold. They did this while testing how the front of the tongue responded to the flavours and sensations. The response of the nerve to the sweet sucrose (table sugar) solution was reduced by 50%, but the rats’ responses to salty, bitter, sour, and umami flavours, as well as to touch and cold, were unaffected.
“This is not a subtle effect,” Dus said. “It is really strong, and it only took four weeks.”
The researchers discovered that the rats did not acquire weight from sugar at the end of the four-week period. The rats were subsequently returned to their regular diet of plain water by the researchers. They retested the rats’ sensitivity to sweetness after another four weeks and discovered that it had returned.
“That’s potentially good news for us,” Dus said. “If you eat a lot of sugar, but decide to cut out sugar, this shows you can recover your taste (assuming the system works the same).”
Dus noted that this outcome was fairly anticipated. In the past, Mistretta and Bradley discovered that the taste system is highly malleable and may bounce back after pharmacological therapies like chemotherapy. The discussion then focused on the potential causes of this. The structures that contain the taste buds on the tongue, known as taste papillae, were not altered when scientists examined the rats’ tongues. Dus noted that this made sense since if they had, they would have probably discovered modifications to the rats’ sensitivity to other flavours as well. Additionally, neither the quantity of taste buds on the tongue nor the way the nerve connected to the taste buds changed, according to the researchers.
However, when scientists examined the taste buds of the rats given a high-sugar diet, they discovered fewer cells that recognised sweetness.
Future research by Dus and Ferrario will focus on how these taste modifications impact eating and the activity of brain cells that process sweetness information. For instance, Dus discovered previously that reduced sweet taste in flies dampens the release of dopamine, reducing fullness and inciting overeating. Does the rat also experience this?
The effects of sugar and fat diets on dopamine and the food learning systems in the brains of humans and other mammals are well documented, but it is still unclear what causes these changes. Do they result from changes in our senses, specifically the alterations in taste that we have just observed?
“Because we are mammals and our taste systems are similar to rats, this is the best available evidence that a high-sugar diet is changing the sensory system,” Dus said. “So this might affect your food choices. This might affect your metabolism. But also, the other important implication is that if your taste system is truly plastic, it’s likely that if we reformulate foods to contain less sugar, our taste buds are going to learn to eat and like the food as much as we enjoyed that extra sugary stuff today.”