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updated: 10/10/2012 6:28 AM

Ask the Nutritionist: Upping your fiber intake can decrease risk of colon cancer

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Q. Does current research still support eating more fiber as a way to reduce colon cancer risk? If so, does it matter what type of fiber?

A. Yes, each additional 10 grams of dietary fiber per day is linked with a 10 percent decrease in risk of colorectal cancer, according to the latest Continuous Update Project report from the American Institute for Cancer Research, which is an ongoing analysis and updating of research.

We used to think that the colon cancer protection came only because of how fiber can affect carcinogens by speeding their passage and adding bulk to dilute their concentration in the gut. Now we see that fiber can also act as a "prebiotic", supporting growth of health-promoting bacteria in the gut. Studies suggest that changes in diet can produce changes in gut bacteria within weeks.

In addition, when fiber slows down how fast carbohydrate is absorbed from the digestive tract, it can lead to slower and lower rises in insulin. This can reduce cancer cell growth that occurs with high insulin levels.

Foods supply different types of fiber and each seems to act in slightly different ways to promote health and reduce cancer risk. By getting dietary fiber from plant foods -- vegetables, fruits, whole grains, beans, nuts and seeds -- you are also getting a variety of nutrients and protective natural compounds. So even the same amount of fiber from fiber supplements won't give you the same benefits as food.

Observational studies also show that people who eat diets higher in fiber are more likely to be a healthier weight compared to those who don't eat as much fiber. It's difficult to know for sure how much of the lower cancer risk among people eating more fiber stems from fiber itself, and how much comes from other compounds in those foods or from a lower prevalence of overweight.

So unless your physician has recommended boosting a specific type of fiber for other medical reasons, aim to include plenty of a wide variety of fiber-containing plant foods without zeroing in on any single source.

Q. I love to go out for Greek food, and I know the Mediterranean diet is very healthy. How reasonable are the calories in the restaurant options?

A. Traditional Greek and other Mediterranean eating patterns are extremely healthy, because they focus on plant foods like vegetables, beans and grains (which traditionally were nutrient-rich whole grains). The primary source of fat is olive oil, a healthy choice.

Unfortunately, the amount of fat restaurants use in some dishes is extremely high. Steer clear of options like moussaka, with rich ground meat and oil-drenched eggplant baked in a creamy sauce. Focus on lean, vegetable-laden choices like chicken souvlaki or fish served with grilled vegetables, or the many lentil- and bean-based soups.

For a delicious Greek salad without excessive calories, order it light on the feta cheese (especially if you are ordering another dish that will supply your protein). Just because you're offered a large portion of rice and unending pita bread does not make it a good idea to eat it all. Although tzatziki sounds healthy (Greek yogurt, cucumber and garlic), it's often made with full-fat yogurt that's concentrated in calories, so watch your portion.

Greek restaurants offer delicious meals that may inspire you with new ideas for preparing beans and vegetables at home. Just don't let the "halo" effect of how healthy it seems lead you to forget the impact of portion size if you are trying to keep calories moderate.

• Provided by the American Institute for Cancer Research.

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