The ingredients that lend a smooth, stable consistency to ice cream, chocolate bars, and other packaged snacks may promote certain chronic inflammatory diseases. That’s the claim of a new study, which finds increases in metabolic disease and intestinal inflammation in mice fed two common emulsifiers used in processed food. The authors are a long way from confirming similar effects in humans, but they suggest that these ingredients cause damage by disrupting the barrier between the immune system and the microbiome—the collection of microbes that inhabit our bodies.
The finding, published online today in Nature, is “believable and remarkable,” says Karen Madsen, a microbiologist at the University of Alberta in Edmonton, Canada, who wasn’t involved in the study. “It sends a really clear message that changes to our food supply are altering our microbiota and our health.”
Gut microbes help us fight off infections and resist allergies, but there’s one thing we don’t want them to do: touch our intestinal lining. “Those trillion bugs have kind of got to be kept away from us,” Madsen says. Normally, a layer of mucus separates intestinal cells from gut bacteria. But if bacteria reach these cells, they can stimulate the immune system and cause inflammation. This out-of-control inflammation of the digestive tract is the hallmark of inflammatory bowel disease (IBD), which causes diarrhea, fatigue, and abdominal pain. Chronic inflammation has also been associated with metabolic syndrome—a cluster of co-occurring conditions, including obesity and high blood pressure, that increase a person’s risk of heart disease and diabetes.
Benoit Chassaing, a microbiologist at Georgia State University in Atlanta, wondered if such a bacterial invasion could explain what he describes as a “perfect correlation” between the increasing use of food additives in industrialized countries and the incidence of IBD. (The disease affects more than a million people in the United States and appears to be on the rise.) Work by other groups led Chassaing and colleagues to focus on emulsifiers—detergentlike compounds that coax into a smooth, creamy mixture ingredients that might otherwise prefer to separate, like the milk fat and water in ice cream. A 2009 study found that feeding the emulsifier carboxymethylcellulose (CMC) to genetically engineered mice that were already predisposed to intestinal inflammation led to excess growth of bacteria in their small intestines and increased inflammation.
In the new work, the researchers fed two common emulsifiers, CMC and polysorbate 80, to both a genetically susceptible mouse strain and wild-type mice—those without genetic mutations that would put them at increased risk of IBD or metabolic syndrome. Among the susceptible mice, eating or drinking emulsifiers for 12 weeks increased the risk of developing symptoms of colitis—a mouse model of the intestinal inflammation seen in humans with IBD—from 40% to 80%. The wild-type mice didn’t develop colitis, but showed low-grade inflammation in their intestines and several features of metabolic syndrome: slight weight gain, increased body fat and food intake, and higher blood sugar levels, which indicate poor glucose regulation associated with diabetes.
How emulsifiers induce these changes is still unclear, but the study offers a few hints. Microscopic imaging of the intestines revealed that the average distance between gut bacteria and the intestinal cells was reduced by more than half; bacteria seemed to be advancing toward the gut lining. And the feces of emulsifier-fed mice showed higher numbers of bacterial species known to digest and penetrate mucus. The feces also seemed to contain a more “pro-inflammatory” microbiome, meaning bacteria more strongly activated receptors that trigger inflammation—though it’s not yet clear which bacteria have this effect. Chassaing’s conclusion: Either the emulsifiers damage the mucus layer directly, leaving it vulnerable to bacteria, or they change the composition of the microbiota, favoring the mucus-penetrating microbes.
It’s not at all surprising that these substances have an effect on the gut microbes, says Mia Phillipson, a physiologist at Uppsala University in Sweden who studies intestinal inflammation and bacteria-mucus interactions. Everything from being vegetarian to being born by cesarean section can change the composition of our microbiome in meaningful ways, she notes. But relatively few studies to date have observed the effects of food additives on the microbiome in this level of detail. “I think we’re just on the verge of realizing how important this is,” she says. As for the implications in humans, Phillipson says it’s too early to make broad recommendations, but she suggests that people with IBD or a family history of the disease consider avoiding these ingredients.
Chassaing, too, is careful not to cast these emulsifiers as the ultimate villain. “Of course, society changed so drastically during the last century … and so many other factors were used in food that we can’t really know yet which one is playing the most important role.” His group is now preparing a more ambitious study that compares the microbiomes of people who completely avoid emulsifiers for several weeks with those on a standard Western diet.