Dr. Walter C. Willett is the Fredrick John Stare Professor of Epidemiology and Nutrition at Harvard School of Public Health and a founding investigator of the Nurses’ Health Study II. He spoke about diet and cancer at NCI on February 22-23 as a Division of Cancer Epidemiology and Genetics Visiting Scholar.
What have we learned from the completed long-term studies of diet and cancer risk?
There are still many specific components of diet that do seem to be important for cancer prevention, such as keeping red meat consumption, particularly processed meat, relatively low. The total percentage of calories in the diet from fat doesn't seem to be important. There may still be some modest benefit of higher fruit and vegetable intake for cancer prevention, but it's not the 'big bang' it was thought to be 15 or 20 years ago.
But it's also important that we don't adopt a lifestyle just for preventing one disease, and we particularly have to pay attention to cardiovascular disease, as that is still the number one cause of death. But in general, many of the same things we do for cardiovascular disease are going to have an impact on cancer.
During your visit, you mentioned that prospective observational studies might be
Also, we're often looking at factors that are much more complicated to change than just taking a pill or placebo - to actually change human behavior is difficult. It's not impossible, but to keep the two trial groups separated is the real challenge. That can be a serious problem in a randomized trial, particularly when you're dealing with items that are on the shelves of your grocery store, in pill form or in food form.
What areas of research in the field of diet and cancer are investigators really excited about right now?
Another critical area is milk consumption and calcium intake, because there are now quite a few studies showing that higher intakes of calcium or dairy products are related to increased risk of fatal prostate cancer. And that's important, because the national recommendation to drink three glasses of milk a day would double dairy consumption and production in the United States. As we have no good evidence suggesting it would reduce fractures and quite a few studies showing a relationship with fatal prostate cancer, that's an important area to resolve.Another broad area to explore is the effect of diet during earlier periods in life. There is much indirect evidence that diet is likely to have an important effect during that period of life.