High-sugar diet desensitizes the tongue to sweet tastes, says rat study
Do people eating lots of sugar become desensitized to sweetness? Scientists at the University of Michigan (U-M) have found evidence that this might be the case, with a new study in rats finding that those on a high-sugar diet had as much as a 50% reduction in responsiveness to sweet flavors.
It seems like a logical and anecdotal assumption to make that long-term exposure to a sensation would dull the response to it, but whether it has any scientific basis remained to be seen. Previous studies had found evidence in fruit flies, while another tested the inverse in humans, surveying volunteers about whether they perceived foods as tasting sweeter after going without sugar for two weeks.
For the new study, the U-M researchers investigated the effect in rats, as well as what physiological process might be behind it. They studied two groups of rats – both were fed the same standard diet, but one group received sweetened drinking water. After four weeks, the scientists used electrodes to monitor the responses of the chorda tympany – the nerve that carries signals from the front of the tongue to the brain – when the rats encountered various flavors and sensations.
The nerves in both groups of rats responded just the same to salty, sour, bitter and umami flavors, as well as to cold and touch sensations. But when they were given a sweet solution, the nerves in the mice that had been on sugar water diet had as much as 50% reduction in responsiveness, compared to the control group on plain water.
“This is not a subtle effect,” said Monica Dus, lead author of the study. “It is really strong, and it only took four weeks.”
Next, the team put the experimental rats back onto regular water, then tested them again after a further four weeks. And sure enough, their sensitivity to sweetness was restored, indicating the effect is reversible and backing up the findings from the previous human test.
The team then investigated what physiological changes might be behind the effect. They found no changes to the number of taste buds nor any changes to the way the nerve connects to them. However, inside individual taste buds they found fewer sweetness-detecting cells in the sugar-water rats than the control group.
Future work will investigate how taste changes like this might affect an animal’s eating habits, as well as physiological effects like the release of dopamine. And of course, more study will need to be done to find out if this mechanism is at play in humans too, and what that might mean.
“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,” said Dus. “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.”
The research was published in the journal Current Biology. The team describes the work in the video below.
Source: University of Michigan
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