Diet makes a difference
Jan. 14, 2005
CANADIAN PRESS The impact of diet on one’s risk of developing cancer may have come into slightly sharper focus this week with the publication of two new studies.
The first adds more weight to arguments that long-term red meat and processed meat consumption increases the risk of some forms of colorectal cancer. The second poured more cold water over the idea that women can lower their risk of breast cancer by eating lots of vegetables and fruit.
The Canadian Cancer Society praised both studies, saying they were large and well-designed pieces of research that will help to answer the questions about the interaction between diet and cancer.
But despite the negative finding on the fruit and vegetable study, a spokesperson said the organization remains committed to promoting a diet high in these important foods.
“We know that eating fruits and vegetables, a healthy diet with high fibre and those types of things will reduce your risk of not only certain types of cancer but also will reduce your risk of other chronic diseases,” said Heather Logan, director of cancer control policy. “Our messaging is not changing.”
The studies, published in the Journal of the American Medical Association, were unusually large nearly 150,000 adults in the meat study and more than 285,000 in the fruit and vegetable study.
Large studies make it easier to ensure that results are statistically significant. Both studies analyzed the food consumption of participants over a number of years more than 22 years in the meat study and an average of 5.4 years in the fruit and vegetable one.
But because cancers take a long time to develop, even those periods might not have been long enough to capture effects of exposure to the foods.
“Although it’s well designed and it’s a credible organization, it really has only followed women for an average of just over five years,” Logan said of the fruits and vegetables study.
“And we know that it takes longer than five years to really see a profound impact at the population level. So they may not have followed women long enough yet to have seen a protective effect.”
The authors acknowledged the possibility.
“We cannot exclude that associations will be found after more years of follow-up,” they said of their work, called the “European Prospective Investigation into Cancer and Nutrition.” The study was led by Dr. Petra Peeters of the University Medical Center of Utrecht, in the Netherlands.
Those authors also suggested it is plausible that high fruit and vegetable consumption might actually be protective for certain sub-groups of women women with a family history of breast cancer, for instance.
And they noted certain specific vegetables or fruits or nutrients within them might still turn out to be beneficial.
The meat study, led by researchers from the American Cancer Society, found that people who consumed large amounts of red and processed meats had a 30 to 40 per cent higher likelihood of developing certain types of colorectal cancers. High consumption of poultry and fish appeared to be protective against those cancers.
An editorial in the journal by a Harvard University nutritional expert said that while the findings were “strongly suggestive” they could not be considered proof positive.
Still, Dr. Walter Willett, author of Eat, Drink, and Be Healthy: The Harvard Medical School Guide to Healthy Eating, said people should keep the findings in mind when structuring their diets.
“The relation between red meat consumption and colorectal cancer may not be conclusive, but prudence would suggest that red meat and processed meats in particular, should be eaten sparingly to minimize risk.
“Replacing red meat with a combination of fish, nuts, poultry and legumes will also reduce risk of coronary heart disease,” Willett wrote.
Logan said an expert panel report due out next year should help interpret the amassed evidence about links between cancer and diet.