Five years ago I changed my diet and started taking probiotic pills to help with digestion. Within days I felt like a new man. But I never thought that a beneficial bacteria supplement might someday be able to help me avoid disease.

For most of his twenty-five-year career, Robert Sandler has been researching the causes of colorectal cancer, the second leading cause of death by cancer in the United States. “I was studying the same things everyone else was—diet, lifestyle, physical activity, family history, medication,” he says. “But the more I studied, the more obvious it was that there was something missing, because the data on diet are pretty inconsistent. Everyone thinks fiber protects against colon cancer. But if you look at the studies, some say it does and some say it doesn’t. About eight years ago I began wondering if gut bacteria play a role.”

Sandler says fiber might protect some people but not others against colon cancer because we all have different bacteria in us that react differently to fiber. He began working with Tope Keku, a UNC researcher who took the lead on clinical studies that try to determine whether bacteria have any say in whether someone gets colon cancer.

In 2010, Keku and Sandler used the Microbiome Core Facility to find that patients with precancerous growths or polyps in their colons have more Proteobacteria than people without the growths. Proteobacteria is a phylum that includes hundreds of species, including E. coli and other pathogenic bugs. Other researchers found that E. coli were more prevalent in biopsies taken from people with precancerous polyps and malignant tumors. And because bacteria fight each other for space in our bellies, the patients with more Proteobacteria and E.coli have fewer beneficial bacteria.

Still, Sandler and Keku can’t yet say that bacteria caused the tumors. It could be that the tumors formed and then the bacterial balance was altered. “I think that’s kind of far-fetched,” Sandler says. “It’s much more likely that bacteria play a role in the creation of the precancerous polyps.”

Keku says, “Something upsets the balance of bacteria. It could be diet that leads to some bacteria growing faster than others. And then maybe those bacteria promote colon cancer.”

To find out, she’s expanding her study to include hundreds of participants, and she’ll use DNA sequencing to get a more precise view of which bacterial species are prevalent in patients with the kinds of polyps that often turn into cancer. She’s also creating animal models to see if certain bacterial genera and species promote cancer growth. And if some do, then there ought to be a way to limit those so-called bad bacteria and promote the good kind to take up residence in our intestines.

It’s not so crazy to think that someday those capsules full of bacteria and those creamy fermented snacks could include the sorts of good bacteria that are proven to prevent the fourth most common form of cancer in the United States.

It would be great to find out what bacteria are missing and introduce them back into our diets,” Keku says. “What a great way to address colon cancer—you could know your risk and lower it by eating yogurt every day.”

Robert Sandler is a distinguished professor of medicine and epidemiology, and chief of the Division of Gastroenterology and Hepatology in the School of Medicine. Matthew Wolfgang is an associate professor of microbiology and immunology in the School of Medicine and a member of the Cystic Fibrosis/Pulmonary Research and Treatment Center.