Cancer Prevention: Rethink Your Diet as Well as Your Smoking

Many cancers could be prevented if Americans quit smoking and ate differently.

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If everyone were to quit smoking today, nearly 450,000 fewer Americans would die annually from smoking-related diseases. Yet even with all the smoking bans across the country, one in five Americans still lights up regularly—a rate that's plateaued since 2005 after four decades of decline, according to a report issued Tuesday by the Centers for Disease Control and Prevention. While the smoking-lung cancer connection is an old story, every week, it seems, another headline tells you what you should or shouldn't eat to avert the "big C". Eat a colorful array of fruits and vegetables to ward off lung cancer, says one recent study; avoid soft drinks if you don't want to die of pancreatic cancer, warns another. Wine is good for your heart, but may increase your risk of breast cancer, others suggest.

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And who wouldn't be willing to give up the Diet Coke or chardonnay to sidestep the disease we fear most? It you took action based on research published this week in the Annals of Internal Medicine, you might find yourself forgoing hamburgers and chicken wings and embracing soy burgers, tofu, and peanut butter instead. That study found that an Atkins-style diet that emphasized vegetable protein over animal protein lowered the risk of cancer. But all things considered, how much do dietary changes really matter in terms of cancer prevention? "Right after smoking, diet ranks right up there as the No. 2 modifiable risk factor," says Demetrius Albanes, a senior investigator and medical epidemiologist at the National Cancer Institute. "Twenty-five percent of cancers can be related back to eating practices." Does that mean we really need to avoid soft drinks if we don't want to get pancreatic cancer, as was suggested by a recent study in the journal Cancer Epidemiology, Biomarkers & Prevention? "I don't think we can say that," Albanes says. "That particular study from Singapore didn't control very well for smoking, which is an important risk factor for pancreatic cancer." In other words, it could be that those who down daily six-packs of Fanta are also more likely to light up.

Therein lies the rub. Unlike smoking, which is clearly carcinogenic, no single food or nutrient really impacts your overall risk of getting a lung or breast tumor, says Albanes, who helped conduct the 1994 clinical trial showing that smokers randomly assigned to take either beta carotene or vitamin E supplements didn't get any less lung cancer than those who were given placebos. It's really about the composition of your overall diet. What's clear, he says, is that the variety of nutrients packed into foods like green leafy produce, orange sweet potatoes, and bright pink nectarines all work in synergy to help the body fend off cancer cells.

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Most likely, following a Mediterranean-style diet based on fruits, vegetables, fish, nuts, and whole grains helps lower your cancer risk. And the latest research suggests that tweaking this plan to include less bread and pasta and more plant protein like soy could have added benefits. "Research shows that a plant-based diet is ideal, the less processed the better," says Alice Bender, a nutritionist at the American Institute for Cancer Research, a nonprofit research organization in Washington, D.C. "Avoid deep-fried foods and added salt and sugar, the sorts of foods that are dense in calories." A good rule of thumb: Two thirds of your plate should be filled with vegetables and legumes, while just one third should provide animal protein. The type of animal protein matters. Try to minimize your intake of deli meats, hot dogs, and other processed meats—which are pretty strongly associated with colorectal cancer—and limit your consumption of red meat to no more than 18 ounces per week since more also increases cancer risk.

[ Wean Yourself Off Processed Foods in 7 Steps] What also matters is how much you weigh and how many calories you burn. Being overweight and inactive appears to foster cell division and proliferation, which may give rise to tumors. Obesity also goes hand in hand with high insulin levels and inflammation, two metabolic states that help cancers grow and spread. "It is just now becoming apparent that obesity is a major risk factor for several cancers," says cancer researcher June Stevens, chair of the department of nutrition at the University of North Carolina. "Physical activity tends to be protective. So people should think about losing weight and being physically active to prevent cancer. Of course, if they lose weight by being more physically active and eating more fruits and vegetables and less red meat and alcohol—so much the better!"