Bread-Heavy Diet Linked to Kidney Cancer

But expert urges caution in interpreting the study results

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By Kathleen Doheny
HealthDay Reporter

FRIDAY, Oct. 20, 2006 (HealthDay News) -- A diet high in bread may boost the risk of kidney cancer, according to an Italian study that compared the food intake of kidney cancer patients and those without the disease.

Researchers say those consuming the highest amounts of bread doubled the risk for kidney malignancy, compared to those eating the smallest amounts.

But one expert urged caution in interpreting the study results.

"These findings need to be replicated and found consistent before any recommendation can be made," Marji McCullough, a registered dietitian and spokeswoman for the American Cancer Society, said in a prepared statement.

The study's lead author, Francesca Bravi, a researcher at the Mario Negri Institute for Pharmacological Research in Milan, agreed. "Further studies are needed to confirm the link between bread and renal cell [kidney] carcinoma," she said.

Her team published the findings in the Oct. 20 online edition of the International Journal of Cancer.

In the study, Bravi's team compared 767 men and women, aged 24 to 79, with kidney cancer to 1,534 men and women in the same age range who did not have the disease.

They asked about diet, lifestyle, personal and family medical history and obtained the participants' height and weight so they could compute their body-mass index (BMI). The participants also answered questions on average weekly intakes of 78 food items over the past two years.

Those who ate the highest amounts of bread -- 28 portions a week -- had nearly two times the risk of kidney cancer as those who ate the lowest number of portions per week, 9, she found. A "portion" was defined as 50 grams or 1.7 ounces, the equivalent of a slice or a slice and a half of bread.

A modest but not statistically significant increased risk was found for the highest intakes of pasta and rice. Those with the highest intakes of milk and yogurt had a 1.3 times greater risk for kidney cancer, she found. But high intakes of poultry, processed meet and vegetables decreased the risk.

Bravi speculated that the elevation in risk linked to high bread, pasta and rice consumption could be due to the blood-sugar raising effects of these foods. Eating large quantities of those foods, she said, may affect the process of getting cancer by influencing the level of substances called insulin-like growth factors, which have been implicated in cancer.

Even though more study is needed, Bravi said, "Our study suggests that a diet poor in refined cereals and rich in vegetables may have a favorable role on the risk of renal cell carcinoma."

She doesn't think the findings would apply to the U.S. diet. "The U.S. diet is richer in proteins and poorer in cereals," she said.

McCullough took issue with the study.

"This study has several limitations that could bias its findings," she said. Among them: the fact that patients were asked to remember their diet going back two years. People with kidney cancer may remember what they ate differently than those without the disease, she said.

And while Bravi attributed the link of high bread intake and cancer with the bread's blood sugar-raising effect, other foods they asked about -- potatoes and dessert for instance -- are also known to raise blood sugar levels. But those foods didn't boost the risk of cancer, McCullough pointed out.

McCullough said that the findings about bread and pasta "need to be replicated and found consistent before any recommendation can be made."

She noted that the amount of bread consumed by the highest 20 percent in Bravi's study isn't excessive. It was also mainly bread made with refined flour, not whole grain.

Possibly, McCullough said, it wasn't the bread consumption, per se, that raised the risk of cancer, but something related to it, such as eating a lot of butter with the bread.

Right now, the best way to reduce kidney cancer risk, McCullough said, is to focus on the known risk factors, such as obesity and smoking, and correct those. "We know that avoiding tobacco and maintaining an ideal body weight are two ways individuals can modify their risk of developing kidney and many other cancers," she said.

About 39,000 people in the United States will learn they have kidney cancer this year, according to the American Cancer Society, and about 12,840 people will die from it.

More information

To learn more about kidney cancer, visit the American Cancer Society.

SOURCES: Marji McCullough, Sc.D., R.D., senior epidemiologist, American Cancer Society, Atlanta; Francesca Bravi, Sc.D., researcher, Mario Negri Institute for Pharmacological Research, Milan, Italy; Oct. 20 2006, International Journal of Cancer

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