A high-sugar diet decreases the ability to sense sweetness in rats

For many people, a high-sugar diet has become almost accidental.

According to University of Michigan researcher Monica Dus, three-quarters of the foods in the supermarket have added sugar, leading the scientist to wonder if our sense of taste can be dulled to sweetness. Now, in a study on rats, a collaboration of UM researchers discovered that a diet high in sugar decreases the taste system’s ability to perceive sweetness.

Dus wanted to further investigate whether this phenomenon is a physiological effect taking place in the senses of rats consuming the high-sugar diet. The group, a collaboration that included UM scientists Robert Bradley, Charlotte Mistretta and Carrie Ferrario, found that the responsiveness of the nerve that carries sweetness information from the tongue to the brain increased in rats fed a high-sugar diet , was reduced by almost 50%. Your results will be published in the journal Current Biology.

“A few years ago, a study showed that reducing the amount of sugar in the human diet made people perceive sugar as more intense. But how does it happen?” said Dus, associate professor of molecular, cellular and developmental biology. “Several of our previous work found that sugar dulls the sweet taste of fruit flies by decreasing nerve responsiveness and reprogramming taste cells, but flies are still just flies. I really wanted to understand if and how it happens in mammals.”

Dus reached out to UM School of Dentistry professors Bradley and Mistretta, who have been studying how taste works and how it is altered by diet and disease. The team also connected with Ferrario, an associate professor of pharmacology at UM Medical School who studies the neurobiology of feeding behavior in rats.

The researchers gave a group of rats their typical diet and access to sugar water. A control group of rats received their normal diet and access to plain water. After four weeks, the researchers used electrodes to record the nerve’s responses when the tongue was stimulated with different solutions. This nerve carries taste information from the front of the rat’s tongue, which contains the taste bud cells that sense chemicals, to the brain.

The researchers then gave the rats sweet, bitter, sour, salty and umami-flavored solutions and measured the rats’ responses to touch and cold. As they did so, they tested the response of the front of the tongue to these flavors and sensations.

The researchers found no difference in the rats’ response to salty, bitter, sour and umami tastes, or to touch or cold, but they did see a 50% reduction in the nerve’s responsiveness to the sweet sucrose solution (table sugar).

“It’s not a subtle effect,” Dus said. “It’s really strong and it only lasted four weeks.”

At the end of the four weeks, the researchers also found that the rats had not gained weight from sugar. The scientists then put the rats back on their normal diet of plain water. After another four weeks, they retested the rats’ sensitivity to sweets and found that it was restored.

“This is potentially good news for us,” Dus said. “If you eat a lot of sugar but decide to cut it out, it shows that you can regain your taste (assuming the system works the same).”

That result was somewhat expected, Dus said. Previously, Mistretta and Bradley found that the taste system is very plastic and can recover from drug treatments that disrupt it, such as: B. Chemotherapy.

The group then addressed the question of why this might be happening. When they looked at the rats’ tongues, they found no change in the rats’ taste buds, the structures that house the taste buds in the tongue. That makes sense, Dus said: If they had done it, they probably would have noticed changes in the rats’ sensitivity to other tastes as well.

The researchers also found no changes in the number of taste buds on the tongue or in the way the nerve connects to the taste buds. But when they looked into the taste buds, they found fewer cells detecting sweetness in the rats fed a high-sugar diet.

In future studies, Dus and Ferrario will examine how these taste changes affect eating and the activity of cells that receive information about sweetness deep in the brain. For example, Dus previously found that in flies, reduced sweetness dampens dopamine release, reduces satiety, and triggers overeating. Does this happen to rats too?

There is much evidence that sugar and fat diets affect dopamine and the food-learning systems in the human and mammalian brains, but the causes of these changes remain largely unknown. Do they arise from the changes in our senses, specifically the changes in taste observed here?

“Since we are mammals and our taste systems are similar to rats, this is the best available evidence that a high-sugar diet alters the sensory system,” Dus said. “So this could impact your food choices. This could 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 and learn to eat and like the food so much, our taste buds will. how we enjoyed the extra sugary stuff today.”

The group wrote a joint internal grant proposing to study how sugar alters sweetness in rats, which funded their work. The work started in 2018, first with student Hannan Driks and then with MCDB postdoc Hayeon Sung and postdoc Iva Vesela at the dental school. The COVID shutdown and subsequent research restrictions halted the project for almost 1.5 years.