Eating red meat may increase a person’s risk of developing the most common type of kidney cancer, while eating vegetables may provide a protective effect, new research in the Journal of the American Dietetic Association shows.

Principal investigator Dr. Nabih R. Asal of the University of Florida, Gainesville and associates also found that people who ate lots of white bread and white potatoes were at greater risk of the disease than their peers who ate these foods less frequently. The relationship was particularly strong among women.

In an interview with Reuters Health, co-author Suzanne Dolwick Grieb said it’s possible these foods could boost cancer risk because of their high glycemic index. Glycemic index indicates how quickly blood glucose rises after eating a particular food. “Foods that have a high glycemic index are known to affect insulin resistance and also insulin-like growth factors,” Grieb noted. “Those two things have been implicated in other cancers.”

Kidney cancer is on the rise in the United States, Grieb and her team point out in their report. The best-documented risk factors for the disease are obesity and cigarette smoking, they add. Studies, to date, on diet and renal cell carcinoma - which accounts for 85 percent of kidney cancers - have had “inconclusive” results.

Grieb and her colleagues investigated whether certain types of foods or food groups might influence the risk of renal cell carcinoma by comparing 335 people with renal cell carcinoma with 337 healthy controls. All of the study participants reported how frequently they ate a variety of different foods.

While eating spinach and other greens, as well as tomatoes, reduced cancer risk in all study participants, especially men, white potatoes - including both fried and non-fried - increased it, the researchers found, with the strongest effects seen in women.

White bread also increased the cancer risk in study participants, with the strongest association seen in women; those who ate white bread five or more times a week were three times more likely to develop renal cell carcinoma than women who ate white bread less than once a week.

The researchers found no relationship between fruit and dairy food consumption and renal cell carcinoma. However, both men and women who ate red meat five or more times a week were more than four times as likely to develop the disease compared to people who consumed red meat less than once a week.

There were not enough African Americans in the current study to look at whites and blacks separately, the researchers note, but future studies of renal cell carcinoma risk factors should look at a variety of ethnic groups, they say, because there are “clear racial disparities” in trends in the incidence of the disease.

SOURCE: Journal of the American Dietetic Association, April 2009.