Foods to eat more of
It has long been suspected that eating more whole grains reduces colon cancer risk. "But now we have enough research to say the link has strong evidence," Giovannucci says.
In fact, eating about three servings of whole grains a day can lower colorectal cancer risk by 17 percent. (One serving is one cup of ready-to-eat cereal, a slice of bread or half a cup of cooked rice or pasta.)
Why do whole grains help? "Fiber is one of the keys to prevention of colon cancer," says Michael A. Valente, a colorectal surgeon at the Cleveland Clinic. "But we suspect that it's really the thousands of nutrients, minerals and other natural chemical compounds present in foods that are high in fiber — such as whole grains and fruits and vegetables — that are helping to prevent cancer, not just the fiber itself."
Many of these compounds have what the report called "plausible anti-carcinogenic properties." Which is why it's smart to consume more fiber-rich fruits and vegetables as well.
Foods to cut back on
The researchers found that eating a lot of red meat (such as beef and pork) and processed meat (such as bacon, cold cuts and sausage) was potentially harmful.
Every 1.8 ounces a day of processed meat increased risk by as much as 16 percent, while eating more than about 17.5 ounces of red meat a week was labeled a "probable cause" of colorectal cancer.
One theory as to why these meats increase colon-cancer risk is that they have high levels of heme iron, which has been shown to promote the growth of colorectal tumors.
The connection between alcohol and colorectal cancer was also "convincing," according to the report, and was especially strong for those who drink more than 30 grams of alcohol (the equivalent of about two glasses of wine, two cocktails or two beers) per day.
"If you do consume alcohol, keep your intake moderate," Giovannucci recommends.
Other steps you can take
Getting more whole grains and veggies, and less meat, may have another risk-reducing benefit: helping you maintain a healthy weight. According to the report, there is strong evidence that people who are overweight are more likely to develop colon cancer.
All types of physical activity — not just formal exercise — were protective, with the most-active people having about 20 percent lower risk of colon (but not rectal) cancer than the least-active.
The report did not cover colon cancer screening, but it deserves mention. Colorectal cancer usually develops over 10 to 15 years without causing symptoms. Most cases start as noncancerous polyps in the lining of the large intestine or the rectum. Detecting and removing polyps prevents them from developing into cancer. You should have a colonoscopy every 10 years starting at age 50.
And if you have a close relative who had colorectal cancer, be even more vigilant about your lifestyle and regular screenings.
"Having a first-degree relative [mother, father, sibling] with the disease increases your risk by nearly 100 percent compared to the average person," says N. Jewel Samadder, a gastroenterologist at the Mayo Clinic and an expert with the American Gastroenterological Association.
If that's you, experts recommend that, in addition to improving your diet, weight and activity level, you start getting colonoscopies at age 40.
Copyright 2017-2018, Consumer Reports Inc.
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