|Whole Grains, Fiber, and Colon Cancer: Some Whole Grains are More “Whole” Than Others
The vast majority of the grain products eaten in the U.S. are refined. When whole grains are refined, for example into white flour or white rice, they are stripped of fiber and micronutrients, leaving behind a calorie-rich, nutrient-poor food. A meta-analysis pooling the data from 6 previous studies has concluded that eating three servings (about 90 grams) of whole grains daily is associated with a 17% decrease in the risk of colorectal cancers. Also, in review of 16 other studies, they concluded that every 10 grams of fiber consumed daily provided a 12% reduction in colon cancer risk.1 So it is the refined grains that could increase one’s risk of colon cancer.2,3 Studies have also linked refined grains with higher rates of breast cancer as well.4,5
The most favorable way to consume grains is with the grain remaining intact. Examples of intact grains are brown and wild rice, wheat berries, barley, quinoa, and steel cut oats. Cooking these grains in water is the most healthful way to prepare them, which also prevents the formation of acrylamide, a potentially toxic compound formed with dry cooking. Intact whole grains can be eaten for breakfast with fruit and seeds or with tomato sauce and onions with lunch or dinner. Whole wheat pasta also has a fairly favorable glycemic load, but bean and lentil pastas are even better, considering the resistant starch content and glycemic benefits of beans.
Also, too much grain, even whole grains can make your diet sub-optimal. The reason for this can be:
- If you eat too many grains, you may not be eating enough beans and green and yellow vegetables, which are more micronutrient dense.
- Most brown rice is contaminated with arsenic-containing agricultural chemicals, which can find their way on to your plate.
- Many whole grain breads, cereals, and crackers are dry cooked and can be browned forming a toxin called acrylamide, which is potentially harmful. High acrylamide intake is associated with several cancers.6-8
- Whole grain pastry flour can still have an unfavorable glycemic load (GL) because it is ground so fine. Many studies have linked high GL foods to increased risk of colorectal cancers.9
Among carbohydrate sources, beans are superior to whole grains with respect to their micronutrient density, glycemic effects, and fiber and resistant starch content.
For example, barley has a GL of 12, and a fiber plus resistant starch content of 35.2%; black beans have a GL of 5 and fiber plus resistant starch content of 69.5%.10,11
Glycemic load (GL)
Fiber + Resistant Starch
|Whole wheat bread
Fiber helps to prevent colon cancer by reducing the contact between dietary carcinogens and intestinal cells via increasing stool bulk and accelerating transit time.12,13 Resistant starch, similar to fiber, is a carbohydrate that is not broken down by human digestive enzymes. Fiber and resistant starch act as prebiotics, fueling the growth of healthy bacteria (probiotics); healthy bacteria in gut the ferment fiber and resistant starch, forming short-chain fatty acids that have a number of anti-cancer effects.14-17 Eating beans, peas or lentils, at least twice a week, has been found to decrease colon cancer risk by 50%.18,19
In summary, intact whole grains are healthful natural foods that contain beneficial phytochemicals. For optimal disease protection, I recommend eating beans every day, avoiding refined grains, and primarily eating whole grains intact and cooked in water (rather than as breads or pastas).
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8. Center for Science in the Public Interest: Acrylamide Product Charts [http://www.cspinet.org/new/pdf/acrylamide_product_charts.pdf]
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13. Gear JS, Brodribb AJ, Ware A, et al: Fibre and bowel transit times. Br J Nutr 1981;45:77-82.
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