BOSTON (CBS) - Who hasn't heard that eating a lot of fruits and vegetables can help you fend off cancer?
Dr. Walter Willett, a leading expert on nutrition and health at the Harvard School of Public Health, says your diet may play less of a role in cancer prevention as originally thought. "As better data have come along," he says, "the benefits for cancer don't look nearly as impressive."
And fat doesn't appear to be as bad as once thought for promoting cancer either. "There had been a strong belief that fat in our diet was the major cause of breast cancer, colon cancer, prostate cancer and other cancers as well," Dr. Willett explains, "but what's emerged as the data have come in is that total fat is not importantly related to any cancer."
Does that mean that eating healthy doesn't matter anymore? Dr. Willett says, "No." "The evidence for benefits of fruits and vegetables for cardiovascular disease and diabetes prevention come from many different sources."
In fact, Dr. Willett says long-term studies show that people who eat five or more servings of fruits and veggies a day have about a 30 percent lower risk of stroke and heart disease.
Which foods pack the most punch? "Blueberries, apples, peaches. There are some that seem to be especially valuable for preventing diabetes and helping us control our weight," Dr. Willett says. And don't leave out the leafy green vegetables like spinach and kale.
Dr. Willett says that the key to a healthy diet, whether you're trying to lose weight or prevent disease, is diversity. "Nutrition is about balance and variety. I think it's analogous to an orchestra. You can't just have one or two good pieces. You've got to have all the pieces together there playing in balance and harmony."
Dr. Willett says that diet in childhood may play a larger role in cancer prevention and that needs to be studied.
In the meantime, diet aside, being overweight increases the risk of several different types of cancer like breast, colon and prostate. And regular exercise is also very important for cancer prevention.
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