A study at Oregon State University, published in the journal Neuroscience, showed that diets high in fat and/or sugar cause changes in gut bacteria that appear related to a loss of ‘cognitive flexibility’. This is the power to adjust and adapt to changing situations. A high sugar diet had the strongest effect, also showing an impairment of long and short term memory.
These problems may be linked to alteration in the microbiome, the complex mixture of about 100 trillion microorganisms living in your digestive system. It is comprised of many different species of bacteria, yeast, fungi and even viruses.
These microbes help us obtain nutrients from foods we normally can’t digest, and also help to protect us from infections by disease causing bacteria. The microbiome in each person changes over time, depending on the food that is eaten. Different microorganisms prefer different food, so species may grow or decline in numbers depending on what you choose to eat. Some people take foods that contain live bacteria, such as yogurt or probiotic supplements. Probiotics must be consumed regularly to maintain the bacteria they contain, or the microbiome may revert to what it was before their introduction.
The study at Oregon State was done by Kathy Magnusson, who tested laboratory mice who consumed different diets. The animals then faced a variety of tests, assessing changes in their mental and physical function. She found that after just four weeks on a high-fat or high-sugar diet, the performance of mice on various tests of mental and physical functioning began to drop compared to animals on a normal diet.
Mice have proven to be a particularly good model for studies relevant to humans on such topics as aging, spatial memory and obesity, according to Dr. Magnusson. Comparable studies in humans would be extremely costly, due to difficulties in recruiting subjects, securing agreement on the assigned diet, and keeping subjects adhering to the plan for weeks.
The mechanisms by which diet can affect behavior is still under study. Bacteria in the microbiome can release compounds that act as neurotransmitters, stimulate sensory nerves and modulate the immune system. It is also possible that the types of fatty acids and carbohydrates in a particular diet my be transformed by the microbiome into compounds that enter the blood stream and affect cognition. In the Oregon study discussed here, cognitive impairment in the mice was specifically related to an increased number of one group of intestinal bacteria (Clostridiales) and a loss of two others (Bacteriodales and Lactobacillales). The researchers guessed that the bacteria themselves somehow brought about the brain changes.
Here’s a take-home lesson from this study: think about the importance of your microbiome and protect the good bacteria therein. They thrive on vegetables and fruits, lots of fiber, healthy protein and healthy fats. Don’t send donuts, soda pop or junk food their way. Sugary foods may make your thinking less flexible. Who needs that? We all need to be able to adapt to our world of continuous, rapid change.
Sadja Greenwood, MD, MPH back issues on this blog Leave me a message if you wish
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