Researchers at Oregon State University have conducted a study that indicates that both a high-fat and a high-sugar diet may cause changes in gut bacteria that appear related to a significant loss of the power to adapt and adjust to changing situations. This power, called cognitive flexibility, is mostly affected by high-sugar diet. It also showed an impairment of early learning for both long-term and short-term memory.
Results of this research show that high-sugar and high fat diet can lead to serious damage to cognitive function, when compared to a normal diet. Such results are consistent with previous studies. Scientists now think that such problems may be linked to alteration of the microbiome – a complex mixture in the digestive system of about 100 trillion microorganisms.
The team of researchers used mice models to do experiments. Mice have proven to be excellent models to research such subjects as aging, spatial memory, obesity and others. Mice were fed different diets and then faced a variety of tests, such as water maze testing, to monitor changes in their mental and physical function, and associated impacts on various types of bacteria.
Professor Kathy Magnusson, one of co-authors of the study, said that it is getting more and more clear that bacteria in human gut, called microbiota, can communicate with the brain. She explained that “Bacteria can release compounds that act as neurotransmitters, stimulate sensory nerves or the immune system, and affect a wide range of biological functions”. However, scientists still are not sure what messages are being sent, what pathways are being used and what effects does this process has.
During this study, mice, which received a high-fat or a high-sugar diet for four weeks, started performing worse in various tests of mental and physical function, compared to control group of mice fed with normal diet. Decreasing cognitive flexibility was one of the most pronounce effects of high-fat or a high-sugar diet. Cognitive flexibility may not be easy to understand for everyone. But scientists compare it an obstacle on your usual route home.
Scientists suggest imagining driving home on a very familiar route, which you use virtually every day. One day you find out that this road is closed – there may be some road works, events taking place or other obstacles, preventing you from using your usual route. A person with high levels of cognitive flexibility would not find this change to be a big problem and would immediately adapt to the change, determine the next best route home, and remember to use the same route the following morning. On the other hand, a person with impaired cognitive flexibility would find task to find a new route a very hard task.
During this research scientists used relatively young animals to test high-sugar and high fat diet on strong and healthier biological system, which is better able to resist pathological influences from their microbiota. But the effect on cognitive flexibility was still observed, despite young organisms of the mice. Scientists say the effect might be even more pronounced with older animals or humans with compromised intestinal systems.
High-sugar and high fat diet is often called “Western diet”. Foods with lots of sugar, fat or simple carbohydrates were linked to a range of chronic illnesses, including the obesity epidemic and an increased incidence of Alzheimer’s disease. But we all knew that such diet is not good for human body for a long time. However, this new study shows that it also affects cognitive function and behaviour, which is one more reason to watch what you eat.