Lab Study: Purple Sweet Potatoes as Colon Cancer Fighters

Purple sweet potatoes (yes, purple) are packed with flavor, fiber, and flavonoids—and are especially high in anthocyanins, the deeply pigmented flavonoid phytochemicals found in many blue, red, or purple fruits, vegetables, and grains such as berries, red grapes, red cabbages, and black rice.purpPot_canstockphoto11111336

Now, a new lab study suggests that these brilliant-colored tubers are actually cancer-fighting powerhouses that may play a role in protection from colorectal cancer.

The study, published in Molecular Nutrition and Food Research, examined the role of a specially bred anthocyanin-rich purple sweet potato (with the secret agent-like name “P40”) in colorectal cancer prevention.

The authors of the study conducted two experiments. First, they compared the cancer-fighting effects of three different sweet potato varieties—a cream-fleshed potato called “O’Henry,” a purple-skinned, white-fleshed potato called “NC Japanese,” and the brilliant purple-skinned and purple-fleshed P40—when added to the diets of mice. They injected the mice with a known carcinogen and placed the mice into groups to receive a diet enriched with O’ Henry, NC Japanese, P40, or regular mouse chow, which served as a control.

Six weeks later, they examined the colons of the mice and counted the number of aberrant crypt foci (ACF), early signs of changes in the colon that can lead to cancer.  They classified the ACF as small, medium, or large. It turns out that the mice eating the P40 enriched diet had significantly reduced numbers of large- and medium-sized ACF compared to the other groups.

In the second experiment, the scientists compared the effects of anthocyanin extracts from P40 and a control (one commonly found in berries and other red fruits) on human colon cancer cells. They observed that the P40 extract inhibited the growth of colon cancer cells significantly more than the control. The anthocyanins in the purple P40 potato appeared to interrupt the normal cycling of the cells’ growth rather than kill the cells, giving them the opportunity to “reprogram” and repair their own DNA.

The scientists had two theories as to why P40’s anthocyanins were superior to the control anthocyanins in terms of health effects. They suggested that whereas the anthocyanins in berries and other fruits usually stand alone, the anthocyanins in P40 are different—they are acylated, which means they are attached to other phytochemicals. Scientists believe that acylation provides anthocyanins an added measure of stability that helps prevent them from breaking down during cooking and other food processing. This stability also means that acylated anthocyanins aren’t broken down by the body until they reach the colon—where they have their greatest effects.

The scientists also suggested that P40’s unique mixture of anthocyanins might have a synergistic effect that makes them superior.

Whatever the case, purple sweet potatoes such as P40 offer a mother lode of anthocyanins. Compared to the other types of sweet potatoes used in the study, P40 contained twice the variety of anthocyanins and nearly four times the total content—eight anthocyanins in all!

The purple sweet potato is a staple food that is grown and eaten in many parts of Asia, Africa, and the Pacific islands. Purple sweet potatoes have the same buttery, sweet flavor of their better-known orange cousins and can be prepared and eaten in much the same way. They are available in many grocery stores and may offer a tasty, cancer-fighting punch to your diet.

Teresa L. Johnson, MSPH, RDN, is a nutrition and health communications consultant with a long-time interest in the role of plant-based diets and cancer prevention. Her work draws on elements of nutritional biochemistry, phytochemistry, toxicology, and epidemiology.