A high fat diet, which changes the mix of bacteria in the gut, alters behaviour and produces signs of brain inflammation – even in the absence of obesity, according to a study.

Researchers from Louisiana State University published a study in Biological Psychiatry, which tested whether an obesity-related mix of bacteria in the gut, also known as the gut microbiome, alters behaviour and cognition even when participants were not obese.

Non-obese adult mice on a normal diet received a transplant of gut microbiota from donor mice that had been fed either a high fat diet or control diet. The recipient mice were evaluated for changes in behaviour and cognition.

The animals that received the microbiota shaped by a high fat diet showed multiple disruptions in behaviour, according to the study. These changes included increased anxiety, impaired memory and repetitive behaviour. Other detrimental effects were increased intestinal permeability and markers of inflammation in the brain.

“This paper suggests that high fat diets impair brain health, in part, by disrupting the symbiotic relationship between humans and the microorganisms that occupy our gastrointestinal tracts,” said Dr John Krystal, editor of Biological Psychiatry.

While the mechanisms by which gut microbiota affect behaviour are not well understood, these findings suggest that the gut microbiome has the eventual potential to serve as a target for neuropsychiatric disorder therapies.

High fat diets have long been known to increase the risk of medical problems, such as heart disease and stroke, but this research shows the implications of high fat foods on the risk of depression and other psychiatric disorders.