News Release 31-Mar-2021
New research shows how high consumption affects learning, memory
University of Georgia
Sugar practically screams from the shelves of your grocery store, especially those products marketed to kids.
Children are the highest consumers of added sugar, even as high-sugar diets have been linked to health effects like obesity and heart disease and even impaired memory function.
However, less is known about how high sugar consumption during childhood affects the development of the brain, specifically a region known to be critically important for learning and memory called the hippocampus.
New research led by a University of Georgia faculty member in collaboration with a University of Southern California research group has shown in a rodent model that daily consumption of sugar-sweetened beverages during adolescence impairs performance on a learning and memory task during adulthood. The group further showed that changes in the bacteria in the gut may be the key to the sugar-induced memory impairment.
Supporting this possibility, they found that similar memory deficits were observed 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 Emily Noble, assistant professor in the UGA College of Family and Consumer Sciences who served as first author on the paper. “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.”
Guidelines recommend limiting sugar
The Dietary Guidelines for Americans, a joint publication of the U.S. Departments of Agriculture and of Health and Human Services, recommends limiting added sugars to less than 10 percent of calories per day.
Data from the Centers for Disease Control and Prevention show Americans between the ages 9-18 exceed that recommendation, the bulk of the calories coming from sugar-sweetened beverages.
Considering the role the hippocampus plays in a variety of cognitive functions and the fact the area is still developing into late adolescence, researchers sought to understand more about its vulnerability to a high-sugar diet via gut microbiota.
Juvenile rats were given their normal chow and an 11% sugar solution, which is 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,” Noble said.
A second memory task measured basic recognition memory, a hippocampal-independent memory function that involves the animals’ ability to recognize something they had seen previously.
In this task, sugar had no effect on the animals’ recognition memory.
“Early life sugar consumption seems to selectively impair their hippocampal learning and memory,” Noble said.
Additional analyses determined 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 better identify the mechanism by which the 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,” Noble said.
Noble said future research is needed to better identify specific pathways by which this gut-brain signaling operates.
“The question now is how do these populations of bacteria in the gut alter the development of the brain?” 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.”
The article, “Gut microbial taxa elevated by dietary sugar disrupt memory function,” appears in Translational Psychiatry. Scott Kanoski, associate professor in USC Dornsife College of Letters, Arts and Science, is corresponding author on the paper.
Additional authors on the paper are Scott Kanoski, Elizabeth Davis, Linda Tsan, Clarissa Liu, Andrea Suarez and Roshonda B. Jones from the University of Southern California; Christine Olson, Yen-Wei Chen, Xia Yang and Elaine Y. Hsiao from the University of California-Los Angeles; and Claire de La Serre and Ruth Schade from UGA.
News Release 31-Mar-2021
Research shows how a sugary diet early in life could mean memory trouble later
The study by a team of researchers at USC, UCLA and the University of Georgia, Athens, finds a direct connection between particular bacteria in the gut and impaired brain function.
University of Southern California
New research shows how drinking sugary beverages early in life may lead to impaired memory in adulthood.
The study, published today in Translational Psychiatry, also is the first to show how a specific change to the gut microbiome — the bacteria and other microorganisms growing in the stomach and intestines — can alter the function of a particular region of the brain.
According to the Centers for Disease Control and Prevention, sugar-sweetened beverages are a leading source of added sugars in Americans’ diets. Nearly two-thirds of young people in the United States consume at least one sugary drink each day.
Neuroscientist Scott Kanoski, associate professor of biological sciences at the USC Dornsife College of Letters, Arts and Sciences, has studied the link between diet and brain function for years. His research has shown that consumption of sugary beverages impairs memory function in rats and that those same drinks change the gut microbiome.
In the current study, Kanoski and researchers at UCLA and the University of Georgia, Athens, sought to find out if a direct link exists between changes to the microbiome and memory function.
The scientists gave adolescent rats free access to a sugar-sweetened beverage similar to those that humans drink.
When the rats grew to be adults after about a month, the researchers tested their memories using two different methods. One method tested memory associated with a region of the brain called the hippocampus. The other method tested memory function controlled by a region called the perirhinal cortex.
The researchers found that, compared to rats that drank just water, the rats that consumed high levels of sugary drink had more difficulty with memory that uses the hippocampus. Sugar consumption did not affect memories made by the perirhinal cortex.
“Early life sugar consumption seems to selectively impair their hippocampal learning and memory,” said study lead author Emily Noble, assistant professor in the UGA College of Family and Consumer Sciences and a former postdoctoral fellow at USC Dornsife.
The scientists then checked the rats’ gut microbiomes and found differences between those that drank the sweet beverage and those that drank water. The sugar drinkers had larger populations of two particular species of gut bacteria: Parabacteroides distasonis and Parabacteroides johnsonii.
The researchers then asked if the Parabacteroides bacteria could, without the help of sugar, affect the rats’ memory function. They transplanted Parabacteroides bacteria that were grown in the lab into the guts of adolescent rats that drank just water. The rats receiving the bacteria showed memory impairment in the hippocampus when they grew to adulthood much the same as the sugar-drinking rats.
The scientists also found that, unlike the sugar-drinking rats, the transplanted rats also showed memory impairment in the perirhinal cortex. This difference provides further evidence that altered brain function associated with diet may actually be rooted in changes to the gut microbiome.
Previous studies have transplanted the entire gut microbiome from one group of animals to another, producing similar changes to brain function. However, this study is among the first to do so with just two specific species.
“It was surprising to us that we were able to essentially replicate the memory impairments associated with sugar consumption not by transferring the whole microbiome, but simply by enriching a single bacterial population in the gut,” said Kanoski, who is a corresponding author on the study.
Finally, the scientists examined the activity of genes in the hippocampus, comparing rats that drank the sugary beverage to those that drank just water and comparing water drinkers to those transplanted with Parabacteroides.
Gene activity did, in fact, change in both the rats that consumed the sugar-sweetened beverages and the rats transplanted with Parabacteroides. The genes that were affected control how nerve cells transmit electrical signals to other nerve cells and how they send molecular signals internally.
The results of this study confirm a direct link, on a molecular level, between the gut microbiome and brain function.
In future studies, Kanoski and the researchers hope to determine if changing habits, such as eating a healthier diet or increasing exercise, can reverse the harm to memory caused by elevated sugar consumption earlier in life.
In addition to Kanoski and Noble, study authors include Elizabeth Davis, Linda Tsan, Clarissa Liu, Andrea Suarez and Roshonda Jones from USC Dornsife; Christine Olson, Yen-Wei Chen, Xia Yang and Elaine Y. Hsiao UCLA; and Claire de La Serre and Ruth Schade from UGA.
The research was supported by National Institute of Diabetes and Digestive and Kidney Diseases grants DK116942, DK104897, DK118000, DK111158, DK116558, DK 118944 and DK104363; National Institute on Aging award F31 AG064844; and Department of Defense ARO MURI award W911NF-17-1-0402.