Mouse Study: Diets High in Sugar, Fat May Impair Cognition by Changing Gut Bacteria

Consuming a high-fat and/or high-sugar diet causes changes in gut bacteria that appear to be linked to a significant loss of cognitive flexibility, according to a new mouse study at Oregon State University (OSU). The effects were most severe on a high-sugar diet, which was also linked to a deficit in early learning for both long-term and short-term memory.

“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.”

For the study, laboratory mice consumed different diets and then faced a variety of tests, such as water maze testing. Researchers monitored any changes in their mental and physical function as well as the associated impacts on various types of bacteria.

After just four weeks on a high-fat or a high-sugar diet, the performance of mice on various tests of mental and physical function began to drop, compared to animals on a typical diet. One of the most pronounced changes was in what researchers call cognitive flexibility.

“The impairment of cognitive flexibility in this study was pretty strong,” Magnusson said. “Think about driving home on a route that’s very familiar to you, something you’re used to doing. Then one day that road is closed and you suddenly have to find a new way home.”

A person with high levels of cognitive flexibility would adapt to the change, determine the next best route home, and remember to use the same route the following morning, all with little problem. With impaired flexibility, however, it might be a long, slow, and stressful drive home.

What’s often referred to as the “Western diet,” or foods that are high in fat, sugars, and simple carbohydrates, has been linked to a range of chronic illnesses in the United States, including the obesity epidemic and an increased incidence of Alzheimer’s disease.

“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.”

Furthermore, this study was conducted with young animals, said Magnusson, which ordinarily would have a healthier biological system that’s better able to resist pathological influences from their microbiota. The findings might be even more pronounced with older animals or humans with compromised intestinal systems, she said.

The findings are published in the journal Neuroscience.

Source: Oregon State University