Eating ultra-processed foods could lead to an increased risk of being diagnosed with precancerous colorectal growths for women under 50, according to new research.

A study, published Thursday in JAMA Oncology, looked at health outcomes for 29,105 nurses under 50 who underwent at least one colonoscopy. Participants were followed from June 1991 until June 2015 and filled out questionnaires about their eating habits every four years. The researchers looked at two forms of precancerous polyps: adenomas and serrated lesions.

Women who had an average of three ultra-processed food servings per day had a 3% risk of a precancerous polyp, while women who had an average of 10 or more ultra-processed food servings per day had a 5% risk, according to the study.

Only about 5% of adenomas are cancerous, according to the Cleveland Clinic, but about 75% of colorectal cancers start as these growths. The study did not find any links between ultra-processed foods and serrated lesions.

"You do see an increase in risk with more servings of ultra-processed food products," said CBS News medical contributor Dr. Céline Gounder, the editor-at-large for public health at KFF Health News.

Ultra-processed foods account for more than half of the average American's diet, according to a report from the Centers for Disease Control and Prevention, even though most dietary guidelines recommend restricting them. Ultra-processed foods have also been linked to dozens of other health issues, including diabetes, sleep issues, heart trouble and early death.

Study participants who ate more ultra-processed foods also had a higher body mass index, and were more likely to have a history of smoking, according to the research. They also tended to have lower levels of physical activity and consume fewer nutrients like fiber and Vitamin D.

"I don't know if there are any good ultra-processed foods," Gounder said. "Clearly the more you're eating, the worse for your health, the higher the risk for various complications."

Ultra-processed foods don't have a set definition, but they often include packaged foods and beverages, items made without many whole ingredients, and less obvious products like condiments and sauces. Study participants who had diets higher in sugars and artificial sweeteners, as well as packaged savory snacks, had higher rates of adenoma development.

The federal government has said it is planning to define ultra-processed foods, Gounder said. In the meantime, a "good rule of thumb is: if you can't pronounce an ingredient on the package, it is probably an ultra-processed food," she said.

Researchers are still working to determine exactly how ultra-processed foods affect the body.

"We think that the ultra-processed foods are changing your microbiome, so those are the bacteria in your gut. So that causes increased inflammation, it can cause increased permeability of the gut wall," Gounder said. "And then secondly, we know ultra-processed foods are associated with an increased risk of obesity and diabetes which we also know increase the risk of various cancers, including perhaps colon cancer."

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