Additives commonly used in processed foods to improve texture and extend shelf life may promote anxiety-related behaviours and make one less social, a study in mice has found. The study, published in the journal Scientific Reports, also showed sex differences in the mice's behavioral patterns, suggesting that emulsifiers affect the brain via distinct mechanisms in males and females.
Though the researchers from Georgia State University in the US could not pinpoint the exact mechanism by which emulsifiers contribute to behavioral changes, they said inflammation triggers local immune cells to produce signalling molecules that can affect tissues in other places, including the brain.
"The gut also contains branches of the vagus nerve, which forms a direct information pathway to the brain," said Geert de Vries, a professor at Georgia State, who led the study.
Previous research by the same team has shown that emulsifiers can cause low-grade intestinal inflammation by altering the composition of gut microbiota, a diverse population of trillions of microorganisms that are vital to health.
Their research has linked emulsifier consumption to obesity, metabolic syndrome and inflammatory bowel diseases such as colitis, conditions whose incidence has significantly increased since the mid-20th century.
In the same period there has also been an increased incidence of behavioral disorders such as autism, leading scientists to theorise that brain function may be affected by environmental exposure to modern chemical substances as well.
The researchers added one of two commonly used emulsifiers, polysorbate 80 and carboxymethylcellulose, to the drinking water of male and female mice.
After 12 weeks, they observed that treatment with emulsifiers altered the gut microbiota of males and females in different ways. They then conducted tests to assess the effects of the emulsifiers on behaviour. The researchers found that emulsifiers altered anxiety-like behaviour in male mice and reduced social behaviour in female mice.
"We are currently investigating the mechanisms by which dietary emulsifiers are impacting the intestinal microbiota as well as the human relevance of those findings," said Benoit Chassaing, an assistant professor at Georgia State.
As to what's driving the differences between male and female behaviour, de Vries said there may be several factors.
For example, there are known sex differences in the immune system, which help govern the composition of bacteria in the gut, and in the way the digestive system processes food. As a result, "adding emulsifiers to the diet will have different consequences for the microbiota of males and females," de Vries said.
"Our data suggest that these sex-specific changes to the microbiota could contribute to the sex differences in behaviour," he said.
The study adds to evidence that food additives should be evaluated for their effect on the microbiome, which is tied up in many aspects of human health. De Vries said the results also confirm that gut health and brain health are intertwined, and that there may be common mechanisms driving the parallel epidemics of obesity, inflammatory gut conditions and behavioral disorders.