IT’S OFTEN CALLED THE “WESTERN DIET” — a meal loaded with fat, sugars and simple carbohydrates. But eating too many of those bacon cheeseburgers, piles of fries and strawberry milkshakes Americans crave has been linked to chronic illnesses like obesity and Alzheimer’s disease.
Now science is connecting the dots between diet and brain function through an unlikely route: your intestine. Researchers at Oregon State University have found new evidence that fats and sugars alter brain function via changes in the microbiome – a complex mixture in the digestive system of about 100 trillion microorganisms.
“It’s increasingly clear that our gut bacteria, or microbiota, can communicate with the human brain,” says Kathy Magnusson, a professor in the College of Veterinary Medicine and a principal investigator with OSU’s 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.”
Flummoxed by Change
For this study, lab mice were fed a range of diets and then tested with mazes and other challenging tasks. Along with changes in mental and physical function, the researchers monitored associated impacts on certain bacteria. After just four weeks on a high-fat or high-sugar diet, the mice showed significant loss of “cognitive flexibility (that is, the power to adapt and adjust to change) compared to animals on a normal diet. The high-sugar diet had the biggest effect, impairing early learning for both long-term and short-term memory, according to Magnusson.
Indeed, cognitive flexibility was one of the most pronounced changes she found.
“The impairment of cognitive flexibility in this study was pretty strong,” Magnusson says. “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 immediately 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 way home.
Of Mice and Men
Mice have proven to be a particularly good model for studies relevant to humans on aging, spatial memory, obesity and other issues, Magnusson notes. This study was done with young animals, 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 says.
“We’ve known for a while that too much fat and sugar are not good for you,” she says. “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.”
The research, published in the journal Neuroscience, was funded by the Microbiology Foundation and the National Science Foundation.
EDITOR’S NOTE: Read more about the links between gut microbes and human health in the fall 2015 issue of Terra magazine, www.blogs.oregonstate.edu/terra, coming in mid-October.