Inflammatory bowel disease (IBD) and metabolic syndrome seem unrelated at first glance. IBD involves chronic inflammation of all or part of the digestive tract, while metabolic syndrome is marked by extra fat around your middle and resistance to insulin, factors that increase your risk of heart disease and diabetes.
But a study led by scientists Benoit Chassaing and Andrew T. Gewirtz of Georgia State University’s Institute for Biomedical Sciences has found a startling link between these two conditions. It could indicate a common cause.
The research, published in the journal Nature, suggests food additives called emulsifiers used in processed foods to improve texture and extend shelf life may be at least partially responsible for both IBD and metabolic syndrome. What’s more, both health problems have reached epidemic proportions around the world. The widespread popularity of emulsifier-containing processed foods might explain why.
The key to this connection appears to lie in changes the food additives cause to the gut microbiota, the diverse population of 100 trillion bacteria found inside your intestinal tract. In a review of research on the gut microbiota published in the journal Physiology Reviews, University of British Columbia microbiologists pointed out that this complex system of microorganisms helps the immune and other body systems run smoothly — when the system is in balance.
But when this internal ecological system is disturbed, illness can follow. And the gut microbiota are thrown out of balance in both IBD and metabolic syndrome, according to Chassaing and Gewirtz.
“A key feature of these modern plagues is alteration of the gut microbiota in a manner that promotes inflammation,” said Gewirtz.
How did emulsifiers become a suspect causing gut microbiota upset in IBD and metabolic syndrome? "The dramatic increase in these diseases has occurred despite consistent human genetics, suggesting a pivotal role for an environmental factor," Chassaing explained. "Food interacts intimately with the microbiota so we considered what modern additions to the food supply might possibly make gut bacteria more pro-inflammatory."
Recognizing that the rates of both IBD and metabolic syndrome have soared since the mid-20th century, the researchers looked for something added to food during that time period. They soon found emulsifiers.
To find out if these food additives caused changes in the gut microbiota in a way that promoted inflammation, Chassaing and Gewirtz set up animal experiments. They added two common emulsifiers, polysorbate 80 and carboxymethylcellulsose, to the diets of mice in proportions representing the amount of the additives used in almost all processed foods.
Eating the emulsifier-containing food changed the animals’ gut microbiota, causing bacteria to enter the thick mucus layer that lines the intestine — a part of the body that normally contains little bacteria. Those microorganisms released substances which in turn activated genes causing inflammation. Mice genetically bred to be prone to IBD soon developed that disease.
There were also mice used in the research that had normal immune systems. When they ate the emulsifier-containing diets, they didn’t develop IBD. Instead, they had milder intestinal inflammation and signs of metabolic syndrome, including overeating, obesity, high blood sugar, and insulin resistance.
To find out if the same thing happens in people who eat diets containing emulsifier-laden processed foods, the researchers are testing additional emulsifiers and planning experiments to investigate specifically what emulsifiers do inside the human body.
In their research paper, they noted this class of food additive could be an important cause of a wide range of diseases linked to chronic gut inflammation. In addition, it could also be making millions of people fat.
"We do not disagree with the commonly held assumption that over-eating is a central cause of obesity and metabolic syndrome," Gewirtz explained. "Rather, our findings reinforce the concept suggested by earlier work that low-grade inflammation resulting from an altered microbiota can be an underlying cause of excess eating."
According to U.S. Food and Drug Administration (FDA), emulsifiers are widely used to give foods the texture and consistency consumers want; without these substances, the oils in foods like salad dressing, mayonnaise, and peanut butter would separate. The additives, generally listed on processed food labels, help products dissolve more easily and make the foods last longer.
The emulsifiers listed by the FDA are approved as safe. However, Chassaing and Gewirtz have questioned whether the current means of testing and approving food additives are adequate enough to spot chemicals that might trigger low-grade inflammation or cause diseases such as IBD in those who are genetically susceptible.
If you are concerned and want to avoid emulsifiers, remember to read labels. The FDA provides information on food additives and a list of emulsifiers here.
March 31, 2015
Christopher Nystuen, MD, MBA