Scientists were able to show in a recent study on mice that emulsifiers can promote metabolic syndrome, obesity and chronic inflammation in the intestine. Doctors working under Andrew Gewirtz and Benoit Chassaing of Georgia State University suspect that the increasing use of emulsifiers in the food industry and the increase of inflammatory diseases in recent decades are closely linked, as they write in the journal Nature. This is because both metabolic syndrome and chronic inflammatory bowel disease accompany change in the composition of intestinal flora.
"Despite the human genome's unchanging state these diseases have increased dramatically. The suspicion that an environmental factor is very likely instrumental in it acquires probability", says Chassaing. He adds: "What we eat has a direct impact on our intestinal flora, therefore we examined whether modern food additives alter intestinal bacteria such that they increasingly promote inflammation".
In their experiments, the scientists tested the effects of two common emulsifiers, polysorbate 80 and carboxymethylcellulose (CMC) on the intestinal flora of mice. They added the substances to the drinking water of mice at a concentration at which they also occur in food (1%).
Emulsifiers change intestinal flora
For 12 weeks the mice ingested the emulsifiers before the scientists investigated the colon of the animals. As with humans many different micro-organisms colonise the colon of mice. Normally the micro-organisms are separated by a layer of mucus from the epithelial cells of the intestinal wall.
If the intestinal bacteria have no association with emulsifiers, some distance from the epithelial cells is always maintained. On average the bacteria approach the intestinal wall up to 25 micrometers, the very minimum appears to be ten micrometers, the researchers say. In the instance of contact with emulsifiers this distance was reduced to half, some bacteria even had direct contact with the epithelial cells. The protective mucus layer was thinner.
However, the bacterial colonies moved not only closer to the intestinal wall, the emulsifiers also changed the composition of the intestinal microbiome: the researchers found a lesser component of the bacteria group regarded to be healthy Bacteroidales. Mucolytic germs like Ruminococcus gnavus or pro-inflammatory proteobacteria seemed, however, to significantly increase in the presence of emulsifiers. The new bacterial flora produced flagellin and lipopolysaccharide to an increased extent, which in turn can activate pro-inflammatory genes via the immune system.
Inflammation strength dependent on predisposition
Mice with a genetic predisposition for inflammatory diseases in particular suffered under the emulsifier-enriched feeding and reacted by expressing colitis. Yet even with wild-type mice, the researchers were able to detect stronger inflammatory reactions. Among the emulsifier-fed animals an increased appetite was the outcome and they also put on weight faster than mice which drank plain water.
Sterile mice do not respond to emulsifiers
"It looks as though emulsifiers delivered to genetically predisposed hosts induce pronounced colitis and with wild-type hosts result in a low-grade inflammation", the researchers write. This inflammation may favour metabolic syndrome.
Sterile mice - meaning animals with a non-colonised gut - did not respond to the emulsifier-enriched diet. When researchers however transplanted the gut flora of mice that had been fed with emulsifiers into the previously sterile animals, these mice also developed intestinal inflammation. This set of events is seen by the scientists as an indication that it is the intestinal bacteria which affect the susceptibility to inflammation and metabolism.
The research team is now working to test more emulsifiers and find out whether the test results can be transferred to humans. Since humans and mice are however very similar with respect to the structure and the functioning of the intestine, it is very likely that emulsifiers cause similar reactions in the human body to those in the animals. The molecular mechanisms underlying these reactions are also something the scientists want to find out in the near future.
But is not excessive eating to blame?
The study in no way refutes the common assumption that overeating promotes the development of obesity and metabolic syndrome, says Gewirtz. "Our test results even go so far as to confirm this assumption. This is because previous work has already shown that low-grade inflammation resulting from an altered intestinal flora may be the reason for excessive nutrition intake".
Emulsifiers are found in numerous foods that consist of processed raw materials - such as sausage, ice cream and chocolate. They ensure a longer shelf life of foods and improved consistency by blending aqueous and fatty ingredients.
The use of food additives has greatly increased in recent years. To examine whether these additives merely are directly toxic or carcinogenic is obviously not enough, the authors warn.
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