Drinking coffee can help ward off type 2 diabetes and may even help prevent certain cancers, a new study shows.

"We're coming from a situation where coffee had a very negative health image," Dr. Rob van Dam of the Harvard School of Public Health, who has conducted studies on coffee consumption and diabetes, told Reuters Health.

Nevertheless, he added, "it's not like we're promoting coffee as the new health food and asking people who don't like coffee to drink coffee for their health."

Van Dam participated in a "controversy session" on coffee at the Experimental Biology 2007 meeting underway in Washington, D.C.

Dr. Lenore Arab of the David Geffen School of Medicine at UCLA also took part, presenting results of a review of nearly 400 studies investigating coffee consumption and cancer risk.

There's evidence that the beverage may protect against certain types of colon cancer, as well as rectal and liver cancer, possibly by reducing the amount of cholesterol, bile acid and natural sterol secretion in the colon, speeding up the passage of stool through the colon (and thus cutting exposure of the lining of the intestine to potential carcinogens in food), and via other mechanisms as well.

However, Arab did find evidence that coffee may increase the risk of leukemia and stomach cancer, with the case for leukemia being strongest.

The findings suggest that people who may be vulnerable to these risks -- for example pregnant women and children -- should limit coffee consumption, van Dam noted in an interview.

Van Dam and his team are looking for which of the "hundreds to thousands" of components of coffee might be responsible for these effects. It's probably not caffeine, he noted, given that decaf and caffeinated coffee have similar effects on reducing diabetes risk.