Most Americans don’t think twice about eating french fries or chicken that has been deep-fried but those with digestive issues will often times steer clear because it causes them discomfort. A new study from the University of Massachusetts shows just how frying oil can trigger troubles in the colon.

Scientists fed mice canola oil that had previously been used in a deep-fryer and the results were alarming. The oil caused an increase in inflammation in the colon, enhanced tumor growth and worsened gut leakage which spread bacteria into the bloodstream.

The results of the study were published in the journal Cancer Prevention Research and should be eye-opening to all, especially those with inflammatory bowel disease (IBD) and colon cancer.

Researcher Jianan Zhang said, “People with colonic inflammation or colon cancer should be aware of this research." But Professor Guodong Zhang stressed, "It's not our message that frying oil can cause cancer." He said rather the results show eating fried foods may cause existing problems to get worse.

"In the United States, many people have these diseases, but many of them may still eat fast food and fried food," Guodong Zhang says. "If somebody has IBD or colon cancer and they eat this kind of food, there is a chance it will make the diseases more aggressive."

The oil for the experiment came from a commercial fryer used to make falafel at an eatery near the University of Massachusetts. It was heated to 325 F during the cooking process which is hot enough to trigger an array of chemical reactions in the oil.

A combination of the used oil and fresh oil was mixed with powdered food for one group of mice and the control group was fed the powdered diet with only fresh oil. Researchers found the frying oil worsened gut leakage, colonic inflammation and colon tumor growth. In fact, Guodong Zhang said the tumors doubled in size from the control group to the study group.

Scientists then isolated the polar compounds from the frying oil to test their hypothesis that the oxidation of polyunsaturated fatty acids, which occurs when oil is heated, is the primary cause of the inflammatory effects. They found the results were very similar when those compounds were fed to the mice as to when the mice were fed the frying oil itself.

While he believes more research is needed before dietary guidelines and public health policies are changed, Guodong Zhang said, "For individuals with or prone to inflammatory bowel disease, it's probably a good idea to eat less fried food."

Click here to read more in Cancer Prevention Research.