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Dear Dietitian - Do high fiber diets help fight cancer?

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PICT Leanne McCrate Dear Dietitian
Leanne McCrate, RDN, LD

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. 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.

Nutrition studies seem even more confusing because nutrition is in its infancy. We have barely scratched the surface of 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 at any other time in history. 

A study of the role of fiber in disease prevention was published in The Lancet in February 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 conducted 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 daily. 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, seeds, and whole grains. As always, choose foods you enjoy. Start with high-fiber cereal, one with 5 grams 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 at lunch (2 grams of fiber). Include one-half cup of beans (7 grams). Finally, enjoy one-half cup of green peas (4 grams) at dinner, and you have 30 grams of fiber for the day. Bon appétit.

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, RDN, LD, 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.