Both high-fat and high-sugar diets can cause changes in gut bacteria that in turn are responsible for  significant loss of “cognitive flexibility,” or the power to adapt and adjust to changing situations, a study has found.
Researchers at Oregon State University said the effect was most serious on the high-sugar diet, which also showed an impairment of both long-term and short-term memory.
The research builds on growing evidence that gut bacteria, or the microbiome, can have an effect on the function of the brain.
“It’s increasingly clear that our gut bacteria, or microbiota, can communicate with the human brain,” said Kathy Magnusson, a professor in the OSU College of Veterinary Medicine and principal investigator with the Linus Pauling Institute.
“Bacteria can release compounds that act as neurotransmitters, stimulate sensory nerves or the immune system, and affect a wide range of biological functions,” she said. “We’re not sure just what messages are being sent, but we are tracking down the pathways and the effects.”
The findings are consistent with some other studies about the impact of fat and sugar on cognitive function and behaviour.
The human digestive system contains a complex mixture of about 100 trillion microorganisms.
“We’ve known for a while that too much fat and sugar are not good for you,” Magnusson said. “This work suggests that fat and sugar are altering your healthy bacterial systems, and that’s one of the reasons those foods aren’t good for you. It’s not just the food that could be influencing your brain, but an interaction between the food and microbial changes.”
