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Does Blending Destroy Fiber?

Smoothies are all the rage, but how does liquefying fruits and vegetables affect their nutritional benefits? Nutrition Diva gets to the bottom of the glass.

By
Monica Reinagel, MS, LD/N, CNS,
February 4, 2014
Episode #270

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Nutrition Diva listener Jeffrey writes:

"I feel like I get plenty of fiber, but I recently heard that blending fruits in a smoothie destroys the insoluble fiber. Am I defeating my health goals by blending the fruit?"

This is a question I get a lot--which is not surprising when you consider the popularity of smoothies and juicing. But I get an equal number of emails from listeners who have heard that blending fruits and vegetables ruptures the cell walls and makes the nutrients more absorbable.  So which is it? Does liquifying your fruits and vegetables make them more nutritious or less? 

To tell you the truth, although these two assertions about smoothies are widespread on the internet, it is tough to find a whole lot of factual backup. But there's an old saying that "You don't have to know everything as long as you know where to look." For help  in answering your questions, I turned to one of the smartest guys I know: Dr. Lee Falin,  host of the fantastic Everyday Einstein podcast, who pointed me toward some great resources. Thanks for the assist, Lee!

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Does Blending Destroy Fiber?

Fiber is not a single nutrient but a whole class of related compounds with similar functions in the body. Even the classification of fiber as either "soluble" or "insoluble" is an oversimplification.  Like sugars and starches, fiber is made up of carbohydrate molecules. Unlike sugars and starches, however, our bodies cannot dissolve the bonds between the individual carbohydrates in fiber, so these carbohydrates don't get absorbed in the digestive system. That's what we mean when we say that fiber is "indigestible." 

See also: What Is the Difference Between Soluble and Insoluble Fiber?

 

Blending, however, does chop fiber into smaller pieces.  How this affects its activity in the body depends on what kind of fiber we're talking about. An article Lee dug up for me in The Journal of Food Science  notes that grinding up wheat bran reduces its ability to hold water, which presumably decreases its effectiveness in promoting regularity. In fact, one study found that supplementing the diet with very finely ground wheat bran actually caused constipation!

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