Everybody knows fiber is good for you right? After all, fiber prevents colon cancer.  Fiber reduces blood sugar. Fiber lowers cholesterol and improves heart health.

There’s just one teensy-weeny problem:

None of that stuff is actually true. 

In this article, I’ll break down the long-standing myths about fiber and reveal why fiber may not be the superfood we’ve all been led to believe.

Myth #1:  Fiber Prevents Colon Cancer

For over three decades now, we’ve been hearing that we should increase our intake of dietary fiber to prevent colon cancer.  Where did this idea come from?  Most likely it was based on the observation that countries with the highest rates of colon cancer also happened to have the lowest intake of dietary fiber.(1) This is correlation, not causation. With this starting point in mind, the media and the mainstream medical community started to recommend higher fiber intakes to ward off the development of colon cancer.

Meanwhile, the scientific community started examining whether this correlation would actually hold up under more testing. Some studies showed a link between dietary fiber intake and rates of colon cancer. Many did not.  Consider the following:

“Such findings were further bolstered by the results of randomized trials—types of studies that many consider the gold-standard of research. These studies took a group of people and randomly assigned individuals to one of two groups. One group was put on a high fiber diet, while the other group followed a lower fiber diet. After 3 to 4 years, the two groups were compared and no difference was found in rates of colon polyps—noncancerous growths that can turn into cancer. Of course, colon polyps are not cancer, but since it’s thought that all colon cancers start as polyps, it is strong evidence that fiber intake has no direct link with colon cancer.” – Harvard School of Public Health http://www.hsph.harvard.edu/nutritionsource/fiber-and-colon-cancer/

As you can see, it’s interesting how the scientific process plays out: A theory is hatched, then tested and further tested until it’s either proven or dis-proven… or at least until we can make a strong case either way. But far too often, those outside of the scientific community get left in the dark, stuck holding the bag of bad information.

At this time, most scientists don’t believe there is a strong link between dietary fiber intakes and colon cancer. And yet, most people still think eating fiber offers protection against colon cancer.

Myth #2:  Fiber Reduces Blood Sugar

You’re waiting in line to check out at your local grocery store. And on this day, you decide to reward yourself with a Snickers bar. So you grab one, buy it and eat it. The Snickers bar contains 27 grams of sugar. Once that sugar gets to your small intestine, nearly all of that 27 grams will be absorbed into the blood stream.

A week later, you’re back in the same store, in the same line… yet again eye-balling a Snickers bar. And once again you find yourself picking up the candy bar and tossing it to the cashier. Only this time, you have an idea. You eat the Snickers bar… and then you eat a bunch of broccoli too. Because you heard that fiber reduces blood sugar and so you’re thinking the broccoli might “save” you from some of the sugar in the Snickers bar.

Success, right?

Not exactly. It’s true that the fiber might slow down the absorption and digestion process. It may even reduce the initial glucose spike. But your body will still absorb the same 27 grams of sugar, even if it takes twice as long to do so. So you haven’t really “reduced” your blood sugar at all. You simply prolonged the process. (2)

Myth #3: Fiber Lowers Cholesterol And Improves Heart Health

The Cheerios people are certainly banking on the idea that starting your day with a heaping bowl of their cereal is good for your heart. On the outside of the box you’ll see proclamations such as “may help lower your cholesterol!” “Clinically proven to reduce cholesterol!” “Can help lower cholesterol & reduce the risk of heart disease!”

And there may be a small grain of truth to those statements. Certain studies show that increasing your intake of dietary fiber results in a slight lowering of LDL cholesterol levels. It is one thing to accept the idea that consuming dietary fiber can lower your cholesterol. But then you must also accept the idea that lowering your cholesterol will register an improvement in heart health.  And that’s not exactly true. In fact, there’s plenty of evidence to the contrary:

From The Japanese Lipid Intervention Trial:

“The highest death rate observed was among those with lowest cholesterol (under 160mg/dl); lowest death rate observed was with those whose cholesterol was between 200-259mg/dl” (3)

From The Honolulu Heart Program Study:

“Long-term persistence of low cholesterol concentration actually increases the risk of death. Thus, the earlier the patients start to have lower cholesterol concentrations, the greater the risk of death.” (4)

From the Framingham Study:

“There is a direct association between falling cholesterol levels over the first 14 years and mortality over the following 18 years.” (5)

In other words, while eating fiber may in fact lower your cholesterol… the jury is still out as to whether or not lowering your cholesterol will actually improve your health.

Final Word

I feel it’s safe to say dietary fiber may have some value… but we don’t know exactly what it might be. I can say that eating copious amounts of cereal and other processed grains simply because “it has fiber” is not a good strategy. Your best bet is to get your fiber from unprocessed, whole foods such as vegetables and fruit while skipping the sugar-coated bran muffins and preservative-laden breakfast cereals.

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Matt Marshall is a fitness writer and researcher committed to uncovering the truth about health and fitness. He shatters myths and reveals the facts about getting fit at
www.FitnessUnderOath.com

 References:

1: http://www.hsph.harvard.edu/nutritionsource/fiber-and-colon-cancer/
2: http://www.gutsense.org/reports/myth.html
3: http://ije.oxfordjournals.org/content/22/6/1038.abstract
4: http://www.thelancet.com/journals/lancet/article/PIIS0140673601055532/abstract
5: http://www.framinghamheartstudy.org/