Subtitles section Play video Print subtitles I'm Shelby Cullinan with toddy's health news. If you want to keep your brain functioning well, you may want to skip the doughnuts. A new study from Oregon State University found that high-fat and high-sugar diets may cause a loss of cognitive flexibility because the two diets affect bacteria in the gut, called the microbiome. In the study, mice were fed either a high-sugar or a high-fat diet for four weeks. After the four weeks the mental performance of the mice dropped. The high-sugar diet had the most serious effects. The mice on this diet had changes in both cognitive flexibility, long-term and short-term memory. The lead study author said that "It’s increasingly clear that our gut bacteria can communicate with the human brain." Bacteria can release compounds that act as neurotransmitters, stimulate sensory nerves or the immune system, and affect a wide range of biological functions." Speak to your doctor about starting a healthy diet plan today.