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

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Published Thursday, February 25, 2021
PICT Leanne McCrate Dear Dietitian
by Leanne McCrate, RD, LD, CNSC

Dear Dietitian,

I just read an article that said 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 Joseph,

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 various parts of the world.  It must also be tested on men and women of different ages. The studies must reveal the same results to be accepted as valid 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 is we are learning more about nutrition now than any other time in history.  

This particular fiber and disease prevention study was commissioned by the World Health Organization (WHO) and reported in The Lancet in February of 2019. Researchers found a 16-24% decrease in rates of heart disease, strokes, type 2 diabetes, and colorectal cancer when comparing people with the highest dietary fiber consumption with those who ate the least amount. Furthermore, there was a 15-30% reduction in death from any cause in the high fiber group. It is important to note the study was done on fiber in food, not supplements (1). As with most nutrition studies, this was an observational study, which does not show cause and effect. Even so, it strongly suggests fiber is a crucial ingredient of a healthy diet.

Researchers assigned high fiber intake as 25 to 29 grams or more of daily fiber. Americans eat about half that amount. 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, nuts, and whole grains. As always, I recommend eating foods you enjoy. Start with a high fiber cereal, one with 5 g of fiber or more per serving.  Add three fruits each day to increase fiber by another 12 grams. You're already up to 17 grams! Next, have two slices of whole wheat bread on your sandwich for another 2 grams. Add 1/2 cup beans (7g) to your lunch. Finally, enjoy 1/2 cup green peas (4g) at dinner, and you have 30 g total fiber for the day. Bon appetit. 

Until next time, be healthy!

Dear Dietitian


  1. Reynolds A, Mann J, Cummings J, Winter N, Mete E, Te Morenga L. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet 2019 Feb 02; 393(10170): 434-445. doi:

Leanne McCrate, RD, LD, CNSC, is an award-winning dietitian based in St. Louis, Missouri. Her mission is to educate consumers on sound, scientifically-based nutrition. Do you have a nutrition question? Email her today at Dear Dietitian does not endorse any products, health programs, or diet plans. may earn an affiliate commission if you purchase products or services through links in an article. Prices, when displayed, are accurate at the time of publication but may change over time. Commissions do not influence editorial independence.

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