There are 95,000 new cases of colon cancer reported in the U.S. each year, according to the American Cancer Society — more than 39,000 of those cases are rectal cancer. Obesity, red meat, alcohol, and inactivity are all considered risk factors for colorectal cancers. But, according to a new study published in Nature, there's one risk factor Americans should pay special attention to: diet.

Researchers discovered that a high-fat diet can produce more intestinal stem cells in mice, and even cause a pool of other cells to behave like stem cells. This is problematic, explained lead researcher Omer Yilmaz, because stem cells and "stem-like cells" are more likely to give rise to intestinal tumors. "Not only does the high-fat diet change the biology of stem cells, it also changes the biology of non-stem-cell populations, which collectively leads to an increase in tumor formation," Yilmaz, who is an assistant professor at MIT, said in a statement.

The research conducted at Yilmaz's lab focuses on the relationship between diet and cancer. Eventually, researchers were curious about the underlying cellular mechanisms of this relationship.

"We wanted to understand how a long-term high-fat diet influences the biology of stem cells, and how such diet-induced changes that occur in stem cells impact tumor initiation in the intestine," Yilmaz said.

Intestinal stem cells last a lifetime, and recent studies have shown these cells are most likely to play a role in developing colon cancer. To investigate, Yilmaz and his team fed a group of mice a high-fat diet (60 percent fat) for nine to 12 months. The amount of fat was inspired by the "typical American diet," which researchers cited consists of about 20 to 40 percent fat.

The results found that eating a high-fat diet let to a 30 to 50 percent increase in body mass compared to a normal diet. What's more, mice eating more fat had more intestinal tumors. Not only did these mice have more intestinal stem cells, but these cells could function without any input from neighboring cells. This means cells were capable of growing in a culture dish completely unsupported.

"You have more stem cells and they’re able to operate independent of inputs coming from their microenvironment," Yilmaz said.

In addition, the research team observed the daughter cells of stem cells, also known as progenitor cells, began to behave like stem cells.

"This is really important because it’s known that stem cells are often the cells in the intestine that acquire the mutations that go on to give rise to tumors," Yilmaz said. "Not only do you have more of the traditional stem cells on a high-fat diet), but now you have non-stem-cell populations that have the ability to acquire mutations that give rise to tumors."

A high-fat diet is only one of many risk factors for colorectal cancer, but it often coincides with obesity and inactivity, two of the other common risk factors. Age is an unavoidable factor that increases the risk of colorectal cancer, but avoiding red meat and processed meat may be an additional way to lower risk.

Source: Beyaz S, Yilmaz O, et al. High-fat diet enhances stemness and tumorigenicity of intestinal progenitors. Nature. 2016.