“The Effects of Alternating Healthy and Unhealthy Diets on Short-Term Memory and the Microbiome: Insights from Rat Studies”

We all know that a healthy diet with lots of fiber, vitamins and not too many calories is a lot better for life and limb than the average delivery meal packed with fat and sugar. But what actually happens to your brain if you alternate a healthy and an unhealthy diet every week?

Junk food, you can hardly escape it in Western society, the temptations are everywhere. Yet most people eat a varied and reasonably healthy diet. We tend to start the week well with lots of fruit and vegetables and little chocolate and chips. But then it’s Friday evening and the wine comes on the table with a block of cheese or a bitterbal. Why not: it’s the weekend, it was busy at the office and we ate healthy all week?

The junk food cycle
Australian researchers have investigated what those unhealthy weekend days do to your short-term memory. To do this, they put a group of lab rats on a dubious cyclic diet. Previous research has already shown that a diet full of sugar and fat is bad for the cognitive skills of rats and humans. The effects of ‘diet cycling’ however, have hardly been investigated. “We wanted to know whether the same amount of unhealthy food, but in different portions and administered over a longer period of time, would also have the same impact on health,” explains Professor Margaret Morris of the University of New South Wales out.

“Our lab has recently been investigating the relationship between a diet high in fat and sugar and the functioning of short-term memory. For this we put rats on different diets and looked at how this affected them,” says Professor Mike Kendig. One group of rats was given only healthy rat food. The other group was fed only unhealthy ‘cafeteria food’ full of fat and sugar for 16 days. Other rats received the same amount of this unhealthy food, but with a few days in between when the diet consisted of healthy rat food. In this way, the effect of longer and shorter diet cycles could be measured.

Gut bacteria
The results were not good. The rats that were forced to eat junk food all showed a poor score on the working memory test, compared to the healthy diet group. In addition, the longer the junk food periods lasted, the worse the animals were at remembering the location of objects in a maze. It is also interesting that clear changes in the gastrointestinal tract were seen in the junk food rats. The microbiome contained fewer different bacterial species and there were more ‘bad’ and fewer ‘good’ bacteria. This effect became greater the longer the period of unhealthy eating lasted. All rats that were served the cafeteria food also gained more weight than their healthy counterparts. It made little or no difference how long the ‘unhealthy cycles’ lasted. In other words, the effect on short-term memory and the microbiome appeared to be independent of weight gain.

How is this possible? It seems that several factors play a role, of which the quality of the intestinal flora is an important one. “Our analysis shows that the presence of two bacterial species is linked to the reduced functioning of short-term memory. Cyclical diets and their effects on the microbiome therefore directly affect the state of memory,” says Kendig.

Inflammatory responses in the brain
“It is clear that the gastrointestinal tract is related to our brain. Changes in the microbiome can therefore affect our brains and behavior,” explains Morris. Another reason may be that an unhealthy diet causes inflammation in the body and in the brain. “We know that inflammatory reactions in the brain can be detrimental to the function of brain parts. In the past, we have also been able to show that the deterioration of brain functions goes hand in hand with inflammation in the brain.”

It strongly seems that junk food affects the structure of the brain. Previous research has already shown that the hippocampus, a brain region that is essential for learning and memory, can shrink under the influence of a diet full of fats and sugars.

Healthy food for healthy brain
One of the main conclusions of the research is that subtle changes in our diet can already have an impact on our thinking and memory. Regular long periods of healthy eating are very important to keep our short-term memory in good working order. “We think this is essential for healthy aging with a well-functioning brain. If we maintain a healthy diet, such as the Mediterranean diet with a lot of variety, fruit, vegetables, low saturated fats and good proteins, we have a better chance of having a good memory,” concludes Morris.