Science —

Common food emulsifiers may be linked to metabolic syndrome

Increase inflammation in the intestines and alter the microbial community there.

Some of the bacterial residents of the gut, outlined in yellow.
Some of the bacterial residents of the gut, outlined in yellow.

Emulsifiers are used in processed foods, drugs, vitamins, vaccines, soaps, and cosmetics. They hold ingredients that generally don't like to be together, like oil and water, in a stable union. They are found in everyday products ranging from mouthwash to ice cream to salad dressing and barbecue sauce.

When emulsifiers first came into vogue, they were classified by the government as GRAS—"generally regarded as safe"—because in animal studies designed to detect acute toxicity and/or carcinogenic properties, they exhibited neither. But their consumption in the Western world has risen dramatically over the late twentieth century, largely in tandem with inflammatory disorders like colitis and metabolic syndrome, a collective suite of obesity-associated diseases. That connection has prompted more refined safety studies on emulsifiers and other food additives.

The results of some of this new work were published in Nature, implicating two specific emulsifiers in the development of colitis and metabolic syndrome in mice. The emulsifiers exert these effects by disturbing a mouse's microbial community.

Normally, the bacterial residents of the intestine are separated from the intestinal wall by a layer of mucus. But when mice were given two emulsifiers, polysorbate-80 and carboxymethylcellulose, the distance between the bacteria and the epithelium was reduced by half because the mucus wall was thinner. Some bacteria were pressed right up against the epithelium, and a few even adhered to it. The emulsifiers also changed the composition of the microbiome, reducing levels of Bacteroidales (species generally considered to be good guys in terms of the host's health) and increased levels of species that degrade mucus.

The composition of the gut microbiome is known to impact immune signaling. Polysorbate-80 and carboxymethylcellulose increased the secretion of pro inflammatory cytokines, which increased the permeability of the gut. These symptoms, along with the disturbed microbiome composition, are both markers of chronic inflammatory diseases like colitis.

In mice genetically engineered to be susceptible to colitis, the emulsifiers induced it; in normal mice they did not. But the constant, low-grade inflammation and disturbed microbiome did make the normal mice eat more, which made them fatter. And the emulsifiers also impaired glycemic control in normal mice. So although normal mice didn't get full blown colitis, they did exhibit signs of metabolic syndrome. None of these effects were seen in germ-free mice, indicating that the emulsifiers achieved them through their influence on the microbiome.

Although further work is obviously needed to assess the effects of emulsifiers on human health, the authors suggest that emulsifiers may have contributed to the enormous increase in inflammatory bowel disease and metabolic syndrome that has occurred over the last half century. However, the researchers note that "this hypothesis does not dispute the commonly held assumption that excess caloric consumption is a predominant factor driving the metabolic syndrome epidemic."

Maybe it's not entirely our fault that we've been eating everything in sight; by messing with our microbiome, the emulsifiers made us do it.

Nature, 2014. DOI: 10.1038/nature14232  (About DOIs).

Channel Ars Technica