Mice that had gut bacteria transferred from other mice fed with a high fat diet changed their behavior in a negative way, exhibiting anxiety or impaired memory. The findings suggest that apart from heart disease and stroke, obesity might put people’s mental health at risk as well.

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Microbiologists have known for some time that different diets create different gut flora – the trillions of bacterial cells live inside you and help your body function in good conditions. The researchers at Louisiana State University believed that a high-fat diet alters the gut fauna in a way that might render negative effects. To test this hypothesis, they served a high-fat diet to mice, then after a while they transferred gut bacteria to mice that were under a normal diet. They found that the obesity-related microbiome alters behavior and cognition even in the absence of obesity.

The mice experienced multiple disruption in behavior, including increased anxiety, impaired memory, and repetitive behavior. Physiological issues were also uncovered, like intestinal permeability and markers of inflammation. In the brain signs of inflammation were also discovered, suggesting these were actually the triggers for the erratic behavior. All of these highlight quite serious mental health problems associated with obesity, independent of the psychological warfare obesity often wages against its hosts who are social and self-inflicting stigma.

“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 tracks,” Dr. John Krystal, Editor of Biological Psychiatry

Just earlier this month, ZME Science reported a study which found two very common emulsifiers – chemicals that stabilize foods and stop products like mayo from separating – could increase the risk of obesity and irritable bowel syndrome. The study on mice found that even in low concentrations, carboxymethycellulose and polysorbate-80 drastically affect the gut bacteria which seems to lead to obesity as well as a number of gut-related problems.

These changes can happen incredibly fast in the human gut—within three or four days of a big shift in what you eat, as reported previously by a study published in Nature. This means that eating high-fat foods for only a couple of days could significantly change your mood and behavior if you previously were on a balanced diet.