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Fiber is important in everybody's diet, right? We all need more, more, more the diet gurus tell us. Or do we?

Americans have been getting lectured about fiber at least since the time of John Harvey Kellogg (1852-1943), founder of the American Missionary Medical College, and inventor of corn flakes, popularized by the cereal company that bears his name.

corn-flakes.jpg

A devout Christian, Kellogg believed that sex was bad, and that masturbation was especially evil. Kellogg encouraged the "treatment" of masturbation in teen-aged boys by circumcision, performed without anesthetic. To discourage masturbation in teen-aged girls and young men, he advocated the removal of the clitoris with carbolic acid.

And Kellogg persuaded millions of like-minded religious people that sexual addiction, especially nymphomania (which for Kellogg, could have been any interest in sex at all), was caused by constipation, the stool in the rectum constantly stimulating the prostate in men and the vagina in women, and the cure for constipation was fiber. As a result, the Kellogg company of his era, although not the Kellogg company of the twenty-first century, created fiber-rich cereals for the abolition of lust in American society.

It didn't work.

However, a number of myths about fiber persist. Here are five of the factually least accurate.

1. Fiber-rich foods improve digestion by slowing down the digestive process.

The reality is, sometimes it is a good thing to slow down the digestive process. If you are a diabetic, and you want to limit the amount of "fast" insulin you have to take with meals, eating small amounts of fiber-rich foods can help you keep your blood sugar levels under better control. Large amounts of fiber, unfortunately, can aggravate a common form of diabetic nerve damage known as gastroparesis, in which food tends to "sit" in the stomach.

For everybody else, however, too much fiber can slow down the digestive process so much that stomach acids can reflux up into the stomach. The insoluble fiber in whole wheat, in particular, can aggravate heartburn, belching, hiccups, and gas.

2. Fiber keeps your body from absorbing sugar.

The small intestine is extremely efficient at absorbing sugars in foods or digested from foods. It only takes an hour (or maybe a few minutes more or less) for the sugar in, say, a bowl of ice cream, to reach your bloodstream. Eating an apple or a fiber bar creates a mass in the small intestine that holds digested sugars so they don't reach the bloodstream quite as quickly. Fiber might delay the arrival of sugars into your bloodstream for 90 minutes to 2 hours

However, the sugar in the food you eat still gets into your bloodstream sooner or later. And because the bacteria in your colon can digest fiber and share some of its sugars with the cells of the colon, you can actually get as much sugar from fiber, surprisingly enough, as from ice cream. It just takes about 24 hours rather than 1 to 2.

3. Fiber speeds the passage of food through the digestive tract, protecting it from cancer-causing chemicals.

Wait a minute--isn't one of the common claims about fiber that it slows down the digestive process? It can't both slow down digestion and speed it up, can it?

No, it can't. Actually, it's fat that speeds up the passage of food through the digestive tract, not carbohydrates, protein, or fiber.

4. Fiber prevents cancers of the digestive tract.

Actually, there are cancer-protective benefits to eating the amount of fiber found in "five a day," five servings of fruits and vegetables per day. Eating small amounts of fiber, especially the fructooligosaccharides, complex carbohydrates found in Jerusalem artichokes, asparagus, bananas, and berries, feeds friendly bacteria, which in turn release a protective compound called butyric acid (also found in butter). But eating larger amounts of fiber isn't found to protect against colon cancer, and is associated with higher rates of stomach cancer.

5. Well, at least fiber protects women against breast cancer by "capturing" excessive estrogen.

Sorry, this isn't what the research shows. A study of 334, 819 women in Europe found no protective role for dietary fiber in either estrogen-receptor positive or progesterone-receptor positive breast cancers.

Continue reading after recommendations

  • Ferrari P, Rinaldi S, Jenab M, Lukanova A, Olsen A, Tjønneland A, Overvad K, Clavel-Chapelon F, Fagherazzi G, Touillaud M, Kaaks R, von Rüsten A, Boeing H, Trichopoulou A, Lagiou P, Benetou V, Grioni S, Panico S, Masala G, Tumino R, Polidoro S, Bakker MF, van Gils CH, Ros MM, Bueno-de-Mesquita HB, Krum-Hansen S, Engeset D, Skeie G, Pilar A, Sánchez MJ, Buckland G, Ardanaz E, Chirlaque D, Rodriguez L, Travis R, Key T, Khaw KT, Wareham NJ, Sund M, Lenner P, Slimani N, Norat T, Aune D, Riboli E, Romieu I. Dietary fiber intake and risk of hormonal receptor-defined breast cancer in the European Prospective Investigation into Cancer and Nutrition study. Am J Clin Nutr. 2013 Feb. 97(2):344-53. doi: 0.3945/ajcn.112.034025. Epub 2012 Dec 26. PMID: 23269820.
  • Monastyrsky, K. Fiber Menace. Ageless Press, 2011.
  • Photo courtesy of XIAOHEI BLACK by Flickr : www.flickr.com/photos/kuroha/2410216223/
  • Photo courtesy of thienzieyung by Flickr : www.flickr.com/photos/thienzieyung/7194550166/