Sorry if we've whetted your appetite. This enticing photo was chosen to illustrate the potential adverse effects of sugar and fat through their impact on intestinal bacteria. Everything is connected in the human body, and it's a well-known fact that these foods aren't recommended as part of a healthy diet. Less well known, is their effect on the brain. Why and through what mechanisms are they harmful? Kathy Magnusson, a professor of veterinary medicine tells us.

Obviously, it's no fun having to constantly monitor one's eating habits. So many foods are declared as being harmful to health that many of us no longer even pay attention. But this study is worth noting because it highlights the direct effect of sugar and fat consumption on our intellectual abilities, and particularly on memory and cognitive flexibility.

These effects were observed on mice who had been subjected to different dietary regimens: a high-fat diet, a high-sugar diet, and a "normal" diet, which served as a control. Throughout the experimental period, the mice were subjected to tests designed to measure cognitive performance. The setup of the study was one conventionally used in behavioral experimentation and consisted of a platform partially submerged in a tank. The mouse, who cannot see the platform, is placed in the water and will eventually swim to the platform in order to rest. Under normal conditions, when healthy animals are used and the platform's position remains unchanged, the mice are able to decrease the time it takes them to reach the platform. Memory is thus tested across trials. The same principle is used to assess cognitive flexibility, except that platform is moved across trials, and the mice must adapt to the new conditions in order to find it.

Kathy Magnusson was thus able to observe longer navigation times for mice in the high-fat and high-sugar diet groups, with an even stronger effect seen in the cognitive flexibility test than in the memory test.

To understand the cognitive flexibility principle, the authors explain: “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.” People with greater cognitive flexibility will immediately adapt and find the best alternative, and will reproduce the behavior on the following days. In contrast, those who suffer from cognitive disorders that interfere with cognitive flexibility have a much harder time adapting and thus experience more stress getting home.

For Kathy Magnusson, these results clearly show that intestinal bacteria are capable of communicating with their host's brain. The bacteria release compounds that act as neurotransmitters by stimulating sensory nerves and the immune system, and thus may play a role in numerous biological functions. Excessive amounts of fats and sugars may alter intestinal flora and consequently influence how our bodies function.