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Dear Dietitian – Does a high-fiber diet help prevent cancer?

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PICT Leanne McCrate Dear Dietitian
Leanne McCrate, RD, LD, CNSC

Dear Dietitian,

I just read an article that said eating a high fiber diet helps prevent colon cancer, but other articles on this topic have said the opposite.  This is frustrating and confusing!  Can you help clear things up?


Dear Joe,

Scientific studies are often confusing because the results are different. Before something becomes clear in science, it has to be tested several times in different cultures in different parts of the world.  It must also be tested on men and women and people of different ages. The studies must reveal the same results in order to be accepted as true by the scientific community. Sometimes this takes several years.

The reason nutrition studies seem even more confusing is because nutrition is in its infancy.  We have barely scratched the surface on most nutrition topics. When a new topic is studied, results often vary until the matter is “hammered out.” The good news we are learning more about nutrition than other time in history.  

This particular study of fiber and disease prevention was commissioned by the World Health Organization (WHO) and reported in The Lancetin January of 2018. Reynolds, Mann, et. al found a 15-30% decrease in total death, rates of heart disease, stroke and deaths related to strokes, type 2 diabetes, colorectal cancer, and deaths related to heart disease when comparing the highest dietary fiber consumers with the lowest consumers. It is important to note the study was done on fiber in food, not supplements.  Also, the study included people who did not already have the before-mentioned diseases.

The target range of fiber intake is 25 - 29 grams per day.  This is about twice the amount Americans eat each day.  When increasing fiber, do so gradually and drink plenty of water. Otherwise, you may feel uncomfortable, and the gas your body produces may make you unpopular. 

Good sources of fiber include fruits, vegetables, and whole grains, and as always, I recommend eating foods you really enjoy. Start with a high fiber cereal, one with 5 g of fiber or more per serving.  Add 3 fruits each day to increase fiber by another 12 grams. You’re already up to 17 grams! Next, have 2 slices whole wheat bread on your sandwich for another 2 grams. Add ½ cup beans (7g) to your lunch. Finally, enjoy ½ cup green peas (4g) at dinner and you have 30 g total fiber for the day. Bon appétit. 


Dear Dietitian

Leanne McCrate, RD, LD, CNSC, is an award-winning Registered Dietitian with over seventeen years of experience. Have a nutrition question?  Email her at