The take-home message: "Eat more fruit, eat less meat, and don't stop eating your vegetables," Gregory Austin, M.D., M.P.H., tells WebMD.
Austin is a gastroenterology fellow at the University of North Carolina at Chapel Hill. He and his colleagues studied the dietary patterns of 725 adults who got colonoscopies.
In a colonoscopy, doctors guide a thin, flexible tube with a tiny camera through the colon, looking for abnormalities including colon cancer and polyps. Some polyps can become cancerous.
Most people in Austin's study were in their 50s or 60s. Colonoscopy showed that 203 participants had at least one adenoma, a colon polyp. The other 522 participants had no adenomas.
Within three months of colonoscopy, the patients were interviewed about their diet and lifestyle.
Austin's team analyzed the amount of fruit, vegetables, and meat that participants said they usually ate.
Participants' dietary patterns fell into three groups.
The largest group included people who ate a lot of meat and skimped on fruits and vegetables. That's the typical American diet, Austin says, adding that a little more than half of the participants ate that way.
The second-largest group included 181 people who reported eating a lot of fruit, little meat, and a moderate amount of vegetables.
The smallest group included 119 people who reported eating a lot of vegetables and moderate amounts of meat and fruit.
"The group that had the lowest risk of having an adenoma was the group that ate a lot of fruit and avoided meat, basically," Austin says.
He notes that "meat" didn't just refer to red meat, but included beef, pork, veal, chicken, fish, frankfurters, and luncheon meat. The study didn't focus on specific foods.
Adenomas were more common and were found at roughly the same rate among the other two dietary pattern groups. The results held when the researchers took other factors into consideration.
Some studies have found that high vegetable intake can be protective [for the colon], while others haven't. Our study didn't find that," Austin says. However, he doesn't rule out the possibility that eating lots of vegetables protects against adenomas.
Participants who ate the most vegetables also ate a moderate amount of meat. Their meat intake may have offset the vegetables' protective effect, Austin notes.
"What would be ideal is if we had a high-vegetable, low-meat group, but that just wasn't something we had in our study," he says.
People shouldn't hesitate to eat vegetables, Austin notes.
"Certainly we don't want people to interpret the findings of our study as any evidence that they should avoid eating vegetables," he says.
There may be other healthy reasons — such as heart benefits — to eat a lot of vegetables, Austin adds.
Participants weren't followed over time, and they weren't asked to change their diets.
"This is sort of a snapshot," Austin says. "What you'd like to be able to do is have people change their dietary pattern and see whether or not it changes their risk."
For instance, he says researchers could ask people with adenomas to change their diet and get a follow-up colonoscopy five years later to check their risk of recurrent polyps.
"No matter what we eat, people should still get screened for colorectal cancer," Austin says.
He says screening should start at age 50; people who are at high risk should begin screening earlier.
The study is scheduled for publication in April's edition of the Journal of Nutrition.
By Miranda Hitti
Reviewed by Louise Chang, M.D.
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