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The Honolulu Advertiser

Posted on: Monday, April 25, 2005

Poi may help fight colon cancer

By Jan TenBruggencate
Advertiser Science Writer

An intriguing new study suggests that poi may have significant anti-colon cancer and pro-immune system qualities — but before you go on an all-taro diet, you should know that the research is extremely preliminary and could be meaningless as a dietary guide.

The steamed and pounded corm of the taro plant, long a staple in the Hawaiian diet, has been likened by culinary detractors to library paste. But it is to Hawaiian palates what rice is to the Asian dinner plate and potatoes are to the Western diet — the essential starch.

In a laboratory experiment, an extract of poi, placed in a test tube with colon cancer cells from rats, inhibited the cancer cells from dividing. The extract, when combined with rat white blood cells, promoted their growth.

But it's way too early to assume that taro products would have similar effects in live rats and mice, much less in humans, said researcher Amy C. Brown, an assistant professor of nutrition at the University of Hawai'i's College of Tropical Agriculture and Human Resources.

"The next logical step would be to conduct studies in live animals," said biochemist Adrian Franke of the University of Hawai'i's Cancer Research Center of Hawai'i. Franke, who was not involved in the taro project, said lots of products have anti-cancer properties in the laboratory, and that alone doesn't mean much.

International cancer specialists warn against looking for the single dietary "magic bullet."

"It is overall dietary patterns, rather than individual chemical compounds found in food, that should probably be seen as the key factors affecting the risk of major chronic diseases such as cancer," says the comprehensive 1997 report, "Food, Nutrition and the Prevention of Cancer: A global perspective," prepared by the American Institute for Cancer Research and the World Cancer Research Fund.

Brown conducted the poi research with Martin Jadus and Jessie Liu, of the Veterans Affairs Medical Center in Long Beach, Calif., and University of Hawai'i medical school student Jonathan E. Reitzenstein. Their report, "The Anti-Cancer Effects of Poi (Colocasia esculenta) on Colonic Adenocarcinoma Cells In Vitro," has been accepted for publication in the journal "Phytotherapy Research."

Previous studies have found that Native Hawaiians have lower rates of colon cancer than other ethnic groups, and Brown, who studies Hawaiian plants, said she thought poi might be involved. Researcher Jadus did the laboratory work that showed a poi extract seemed to cause cell death in rat colon cancer cells, but not in other cells.

It's not known what factor in the poi might be causing the effect, Brown said.

But a worrisome feature in the statistics is that while Hawaiians seem to get colon cancer less frequently, when they do get it, Hawaiian men tend to die of the cancer at higher rates than other ethnic groups. Brown said that may be linked to a failure by many people to get regular medical checkups.

"This is a cancer which people don't talk about," said cancer researcher Brian Issell, a physician and University of Hawai'i medicine professor. "You've got curative options if it's caught early enough."

He said that regular physical exams are critically important for anyone 50 or older, and also for younger people who have families with a history of colon cancer. Brown agreed.

"Whether poi helps in a test tube is interesting on a scientific basis, but the real story is that people need at age 50 and older to see a physician to be checked for colon cancer," Brown said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.