Today’s post is about interesting research out of the University of Southern California, UCLA and the University of Georgia, looking at the relationship of sugary drinks early in life to cognitive issues later on.[i] Here’s a fact that I didn’t know: according to the CDC, sugary beverages are the leading source of added sugar in Americans’ diets and nearly 2/3rds of young people in the country consume at least 1 of these drinks every day.[ii] Astounding, right?
The scientists gave adolescent rats unlimited access to sugar-sweetened beverages, proportionally comparable to what humans drink in both sugar content and calories. When the rats grew to adulthood, their memories were tested using different methods: one test looked at memory associated with the hippocampus and the other looked at memory associated with a brain region called the perirhinal cortex. The hippocampus is known for its “…role in spatial and episodic memory, as well as for learned and social aspects of food intake control…” and is thought to be “…particularly vulnerable to the deleterious effects of Western dietary factors.”
They found that compared to controls, the rats that consumed the sugary drink scored much worse on memory tests involving the hippocampal region: “During the juvenile and adolescent stages of development, a time when the brain is rapidly developing, consumption of diets high in saturated fat and sugar or sugar alone impairs hippocampal function”
But wait, there’s more. The researchers then took a look at the bacterial microbiome composition of the rodents and found some major differences. The sugar-drinking rats had bigger populations of two particular species, Parabacteroides distasonis and Parabacteroides johnsonii.
They took this information to the logical next step: without drinking sugar, could these bacterial species on their own affect the hippocampal memory? The scientists grew the species in their labs and then transplanted them into adolescent rats that drank plain water. Sure enough, the rats that got these transplants showed memory impairment in the hippocampus as adults. What’s really interesting is that these “transplant rats,” as opposed to the ones who drank sugary beverages, had memory impairments in the perirhinal cortex as well, clearly demonstrating that gut bacterial alterations can affect brain function: “These findings are consistent with previous literature in showing that early life consumption of Western dietary factors impairs neurocognitive outcomes, and further suggest that altered gut bacteria due to excessive early life sugar consumption may functionally link dietary patterns with cognitive impairment.”
In both the “transplant” rats, and the ones who actually drank sugary beverages, the scientists found that gene activity changed in those that control how nerve cells transmit electrical signals to other nerve cells.
The researchers plan to test, in future work, whether or not switching to a healthier diet can reverse this harm to memory caused by early consumption of high levels of sugar. In the meantime, this is – pun intended – some serious food for thought.