The digestive tract is home to 100 trillion bacteria. Collectively known as the gut microbiota, these bacteria help with metabolism and maintaining a healthy immune system. Changes in this microbial community can cause chronic diseases.
A thick layer of mucus separates gut bacteria from the lining of the intestine. A research team led by Dr. Andrew T. Gewirtz at Georgia State University wondered whether chemicals that disrupt this mucus barrier might alter the gut microbiota and play a role in disorders associated with inflammation, including inflammatory bowel disease and metabolic syndrome.
Dietary emulsifiers are added to many processed foods to improve texture and extend shelf life. Chemically similar to detergents, they have been shown to alter the mucus barrier and the microbes associated with it. To determine whether these might play a role in chronic diseases, the team fed mice low levels of 2 commonly used emulsifiers, carboxymethylcellulose or polysorbate-80, in drinking water or in food.
Mice fed the emulsifiers for 12 weeks developed low-grade intestinal inflammation and metabolic syndrome—a group of conditions that increase the risk for type 2 diabetes, heart disease, and stroke. Mice that were genetically engineered to be more prone to inflammation and gut microbe changes developed colitis when fed the emulsifiers.
Mice that consumed the emulsifiers had an altered bacterial composition and thinner intestinal mucus, so that bacteria were closer to the cells lining the colon. The mice also had weight gain, increased food consumption, increased fat mass, and impaired glucose handling, a sign of metabolic syndrome.
When the team fed emulsifiers to germ-free mice, which don’t have gut microbiota, the mice showed no signs of gut inflammation, mucus thinning, or metabolic syndrome. This suggests that the effects of the emulsifiers were most likely caused by altering gut bacteria.
When gut microbes from normal, emulsifier-fed mice were transplanted into germ-free mice that hadn’t been fed emulsifiers, the mice developed low grade inflammation, increased fat mass, and glucose intolerance. These results showed that changes in the gut microbiota caused by dietary emulsifiers can drive inflammation and metabolic changes.
“We do not disagree with the commonly held assumption that overeating is a central cause of obesity and metabolic syndrome,” Gewirtz says. But these results suggest that modern additions to the food supply can interact with gut microbiota to influence inflammation, metabolism, and weight.
The group is now testing additional emulsifiers. They are also designing experiments to examine the effects of food additives in humans.