Consumption of emulsifiers, additives widely used in the production of processed foods, promotes inflammatory bowel disease and a cluster of obesity-related diseases known as metabolic syndrome, and may have contributed to the sharp rise in these conditions over the last three decades, says a new study conducted on rats.
The emulsifiers carboxymethylcellulose, often referred to as cellulose gum, and polysorbate 80, also known as Tween 80, add bulk to foods and keep sauces smooth and frozen confections from separating. They plump up fast-food shakes, keep bottled salad dressings creamy, and prevent ice cream from dissolving into an unsightly soup when left out.
They're also used extensively in pharmaceuticals, to improve the consistency of gel capsules, to make pills come apart in the stomach, and to keep medication suspended in fluids.
But when fed to rats in volumes that mimic their widespread consumption in humans, both emulsifiers induced low-grade inflammation, increased weight gain and fat deposition, caused worrisome changes in metabolic function, and changed the mix of bacteria that colonized their digestive tracts, the authors reported.
The new research, published Wednesday as a "Research Letter" in the journal Nature, suggests that the ubiquitous use of emulsifiers in processed foods consumed by Americans "might be contributing to an increased societal incidence of obesity/metabolic syndrome and other chronic inflammatory diseases."
In rats, the consumption of the two emulsifiers appeared to administer a one-two punch to the gut. The detergent-like molecules were found to erode the mucous membrane that lines the gut and provides a buffer between the delicate epithelial cells of the intestinal surface and the garden of microorganisms that flourish there.
The food additives also appeared to alter the composition of gut microbes, not only boosting strains that promote inflammation but driving down strains that check the process.
The study is among the first to explore whether food additives that have been deemed safe by the Food and Drug Administration may have an unrecognized dark side.
The FDA has labeled carboxymethylcellulose "generally recognized as safe" (or GRAS), a category of food additives that has been in long use without evidence of toxicity. Cellulose gum is widely used in foods at concentrations of 2%. The agency has approved the use of polysorbate 80 in certain foods at concentrations of up to 1%.
Led by microbiologists at Georgia State University's Institute for Biomedical Sciences, a team of researchers fed several types of rats concentrations of the two additives dissolved in their water and, separately, in their chow. The three groups of rats -- one group of normal healthy lab rats, a second engineered to have a predisposition to inflammatory bowel disease, and a third engineered to have sterile digestive tracts -- allowed the researcher to discern the conditions under which the emulsifiers caused trouble.
The rats at higher risk of developing colitis responded to the emulsifier-enhanced diet by developing "robust colitis," suggesting that the additives had a pronounced inflammatory effect on them. The response of wild-type rats was more muted, but certainly problematic: Those rats developed evidence of chronic intestinal inflammation, with damage to the delicate epithelial cells linings their intestines. Researchers noted modest but statistically significant weight gain in these rats, and a "marked increase" in fat deposition. They ate more chow, and their glycemic control and glucose tolerance both showed signs of impairment.
In both sets of mice, a clear difference emerged: After the introduction of emulsifiers into their diets, the protective mucus barrier separating the microbiome and the walls of the intestines was thinner.
Only the rats with bowels free of microbiota appeared to be immune to the additives' effects -- evidence, said the researchers, that the inflammation linked to additives is the result of a disturbance in the relationship among the gut microbiome, the layer of protective mucus and the epithelial wall.
In addition to calling into question the wisdom of ingesting either emulsifier (a near-impossibility for anyone who eats food prepared by others), the researchers said their findings should prompt the FDA to reconsider the criteria they use in declaring food additives safe.
FDA safety testing of food additives has generally sought to rule out the possibility that their ingestion would cause immediate poisoning, or that its ongoing consumption would cause cancer, the authors said. The FDA's process, they added, is not designed to detect the effects of daily consumption of an additive on such subtle measures as inflammation and microbiotic diversity -- which research suggest are probably linked.
That, they suggested, should change.
It's not clear whether the emulsifier-induced inflammation seen in rats reflects what goes on in the human gut in response to carboxymethylcellulose and polysorbate 80. Studies in animals suggested that polysorbate 80 could cause anaphylactic shock, and that its injection could disturb development of reproductive organs. But human testing did not bear out such concerns.
The study was funded by the National Institutes of Health and Crohn's & Colitis Foundation of America.