A new study suggests that two common emulsifiers - the "detergent-like" compounds that stop foods such as mayonnaise from separating - could increase the risk of obesity and irritable bowel syndrome in mice.
The emulsifiers in question, carboxymethycellulose and polysorbate-80, are frequently added to processed western foods, and the research found that they could drastically disrupt the gut bacteria of mice - even in extremely low concentrations.
Over the past year, numerous studies have shown that diverse gut bacteria colonies are crucial to our weight, immune system and digestive health. Now the new study, which has been published in Nature, could help explain why gorging on processed foods makes us so fat, and also why inflammatory conditions such as irritable bowel syndrome have increased since the mid-twentieth century.
To work out how emulsifiers were affecting gut bacteria, a team led by Andrew Gewirtz at Georgia State University added the two emulsifiers in varying levels to the drinking water of lab mice. All the different groups ate the same diet - the only change was the concentration of emulsifiers they were consuming.
The researchers found that healthy mice that had been fed the emulsifiers became obese and developed metabolic problems, such as glucose intolerance, regardless of their diet.
And they found that mice genetically engineered to be predisposed to inflammatory gut diseases suffered an increase in the severity and frequency of inflammatory bowel disease after being fed emulsifiers.
These effects were seen even in mice that consumed just one-tenth of the concentration of the emulsifiers that the FDA permits in food products. But the most severe effects were seen in mice that consumed the amount of emulsifiers as people who live on a diet of ice cream.
The researchers then tested the gut bacteria of these animals, and found that those that had eaten the emulsifiers had less microbial diversity in their colons than healthy mice, and they also found evidence that the microbes had moved closer to the cells that line the gut.
As Sara Reardon reports for Nature: "Gewirtz and his colleagues suspect that the emulsifiers can break down the heavy mucus that lines the mammalian gut and prevents bacteria from coming into contact with gut cells. If this happens, the bacteria cause inflammation in the gut, which can also lead to changes in metabolism."
The next step will be to perform human trials, as well as further animal studies, to determine whether these emulsifiers really to pose a risk to our health. Over the past 50 years, no study has conclusively found that food additives are toxic in mammals, but the team believes this could be because large-scale population studies don't look at changes on the gut bacterial level.
But overall, this paper adds to a growing body of work that suggests that processed foods can have negative effects on our gut ecosystem, such as this study at the end of last year which linked artificial sweeteners to glucose intolerance and gut bacteria changes.
"When it comes to people making their own decisions, between our studies and others out there, it's better to eat less processed food," Gewirtz told Reardon.