A diet rich in fat or sugar can influence changes in the gut bacteria that can trigger a decline in brain functions, a new study finds.

The recent findings by Oregon State University researchers provide more evidence to support previous studies suggesting that there is a connection between fatty and sugary diet and cognitive function and behavior.

For the published study found in the journal Neuroscience, researchers studied mice that were randomly given different diets and subjected to various tests to track changes in their brain and body functions and how they affect different types of gut bacteria.

The researchers also analyzed fecal samples from mice before and after the tests to establish gut bacteria composition.

The mice were given the diet for four weeks and experiment results revealed that their body and brain function tests began to decline, as opposed to animals fed with normal diet.

It was also noted that high-sugar diet was linked to a decline in memory function. Furthermore, scientists observed that the most significant changes recorded was found in "cognitive flexibility."

According to Kathy Magnusson, principal investigator of the research and a professor at the university, the impact on cognitive flexibility was "pretty strong."

Magnusson explains cognitive flexibility by citing an example of a person driving home, which is considered a familiar, routine task.

"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," she said in her statement.

A person who has good cognitive flexibility is receptive to changes. In Magnusson's example, the person would immediately be able to plan a new route to get home.

In contrast, those who have poor cognitive flexibility would find the unexpected change in routine to be stressful, and it would take more time for them to reach home.

Magnusson said that it is already known that too much fatty and sugary foods are not good for the body. According to her, the recent work suggests that fat and sugar and disrupt gut bacteria balance and "that's one of the reasons those foods aren't good for you."