BAKED purple potatoes contain compounds that might destroy colon cancer stem cells and limit the spread of cancer, according to a new study supported by the United States Department of Agriculture.

Since potatoes -- no matter what kind or colour -- are frequently consumed baked, the scientists from Pennsylvania State University baked their purple potatoes for the experiment.

Their earlier work had revealed that potatoes -- including the purple ones -- contain resistant starch that is favorite food of friendly gut bacteria.

Bacteria that eat the starch can convert it to beneficial short-chain fatty acids such as butyric acid, says Jairam KP Vanamala of Penn State.

"The butyric acid regulates immune function in the gut, suppresses chronic inflammation and may also help to cause cancer cells to self-destruct," he says.

In the study, the researchers observed that the baked potato extract hindered the spread of colon cancer stem cells and, in some cases, zapped them out entirely.

They fed whole baked purple potatoes to mice with colon cancer and found similar results.

For humans, the research team recommends eating a medium size purple potato for lunch and dinner or one large size one per day.

The researchers believe the compounds that give fruits and vegetables their various, vibrant colors could all be effective in suppressing cancer growth.

"When you eat from the rainbow, instead of one compound, you have thousands of compounds, working on different pathways to suppress the growth of cancer stem cells," says Vanamala. "Because cancer is such a complex disease, a silver bullet approach is just not possible for most cancers."

The next step in Vanamala's research is to test purple potatoes on humans and to see if they help fight other forms of cancer.

Vanamala points out that foods could offer a healthier protection against cancer because side effects are limited in comparison to those of pharmaceuticals.

Purple potatoes could have potential for use in primary and secondary cancer prevention strategies -- primary being general prevention, and secondary refers to preventing relapse for patients in remission.

A paper on the purple potatoes was published in The Journal of Nutritional Biochemistry.