Does Refined Fiber Cause Cancer?

Most Americans could stand to eat more fiber, but a new study suggests that where you get your fiber can have a huge impact on your health. If you’re relying on refined fiber to meet your needs, you could be putting yourself at a higher risk for liver cancer.

WHAT IS REFINED INULIN?

The refined fiber researchers were feeding to mice in this study is refined inulin, a relatively new food additive that the FDA approved over the summer, along with a handful of other added fibers. There isn’t much research yet on how refined inulin impacts human health, but the new FDA guidance means that companies are adding it to processed foods to boost the fiber content.

“The inulin used in this study is coming from chicory root, not a food we would normally eat,” Vishal Singh, a postdoctoral fellow from The University of Toledo and one of the lead researchers in the study, said in a press release. “In addition, during the extraction and processing of the fiber, it goes through a chemical process. We don’t know how the body responds to these processed fibers.” 

Companies add refined fiber—like refined inulin—to naturally low-fiber processed foods, because consumers are catching on that fiber-rich foods improve our health. Previous research shows that a diet that includes plenty of fiber supports healthy bones and digestion while reducing your risk of chronic disease and cancer. That’s why this study’s results were such a surprise.

REFINED FIBER AND LIVER CANCER: AN ACCIDENTAL DISCOVERY

No one was more surprised about the link between refined fiber and cancer than the Georgia State University and University of Toledo researchers conducting this study, though, because that’s not what they set out to study. They were trying to see if a diet rich in refined inulin (a type of refined fiber) helped prevent obesity, which it did for about 40 percent of the mice.

You can imagine their shock when the mice in their study started developing liver cancer. ”The findings shook us,” Dr. Matam Vijay-Kumar, director of the UT Microbiome Consortium and associate professor in the UT Department of Physiology and Pharmacology, said in a press release.

If you needed proof that weight isn’t always an indicator of good health, there you have it.

At this point, the researchers pivoted. Instead of continuing to look at obesity, they tried to figure out what it was about refined fiber that was causing liver cancer in their subjects. They suspect that the issue is the way our gut breaks down refined fiber.

The researchers looked at two sets of mice: one with elevated levels of gut bacteria (a condition called dysbiosis) and one with no gut bacteria at all. The mice with no gut flora didn’t develop liver cancer, suggesting that the way refined inulin ferments when our gut breaks it down is the culprit.

“We importantly demonstrated that soluble fiber, while it generally beneficially impacts health, can also become detrimental, leading to diseases as severe as liver cancer,” Dr. Benoit Chassaing, assistant professor in the Neuroscience Institute at Georgia State said in a press release. “However, we do not want to promote that fiber is bad. Rather, our research highlights that fortifying processed foods with fiber may not be safe to certain individuals with gut bacterial dysbiosis, in whom consumption of purified fiber may lead to liver cancer.”

This is only preliminary research, and animal studies don’t always translate to human health outcomes. What is clear is that there needs to be more research on the link between refined fiber and cancer.