New research has shown that, in rats, daily consumption of sugar-sweetened drinks during adolescence impairs performance on a learning and memory task during adulthood.
The researchers also demonstrated that changes in the bacteria in the gut may be the key to the sugar-induced memory impairment. Evidence in support of this comes from the observation of similar memory deficits even when the bacteria, called Parabacteroides, were experimentally enriched in the guts of animals that had never consumed sugar.
“Early life sugar increased Parabacteroides levels, and the higher the levels of Parabacteroides, the worse the animals did in the task,” said first author Emily Noble, assistant professor, College of Family and Consumer Sciences, University of Georgia. “We found that the bacteria alone was sufficient to impair memory in the same way as sugar, but it also impaired other types of memory functions as well.”
Data from the Centers for Disease Control and Prevention show American children between the ages 9-18 exceed the recommendation of limiting added sugars to less than 10 percent of calories per day, with the bulk of the calories coming from sugar-sweetened beverages.
Since the hippocampus is still developing into late adolescence and plays a role in a variety of cognitive functions, researchers sought to understand more about its susceptibility to a high-sugar diet via gut microbiota.
Juvenile rats were given their normal chow and an 11% sugar solution, comparable to commercially available sugar-sweetened beverages. Researchers then had the rats perform a hippocampus-dependent memory task designed to measure episodic contextual memory, or remembering the context where they had seen a familiar object before.
“We found that rats that consumed sugar in early life had an impaired capacity to discriminate that an object was novel to a specific context, a task the rats that were not given sugar were able to do,” Prof Noble said.
A second memory task measured basic recognition memory, a hippocampal-independent memory function that involves the animals’ ability to recognise something they had seen previously. Sugar had no effect on the animals’ recognition memory.
“Early life sugar consumption seems to selectively impair their hippocampal learning and memory,” Prof Noble said.
Further analysis revealed that high sugar consumption led to elevated levels of Parabacteroides in the gut microbiome, the more than 100 trillion microorganisms in the gastrointestinal tract that play a role in human health and disease.
To determine the mechanism by which bacteria impacted memory and learning, researchers experimentally increased levels of Parabacteroides in the microbiome of rats that had never consumed sugar. Those animals showed impairments in both hippocampal dependent and hippocampal-independent memory tasks.
“(The bacteria) induced some cognitive deficits on its own,” Prof Noble said.
Future research is needed to better identify these gut-brain signaling specific pathways.
“The question now is how do these populations of bacteria in the gut alter the development of the brain?” Prof Noble said. “Identifying how the bacteria in the gut are impacting brain development will tell us about what sort of internal environment the brain needs in order to grow in a healthy way.”
Source: News-Medical.Net
Journal information: Noble, E. E., et al. (2021) Gut microbial taxa elevated by dietary sugar disrupt memory function. Translational Psychiatry. doi.org/10.1038/s41398-021-01309-7.
