DEAR DR. BLONZ: I just read a book that says by blending fruit into a smoothie, you are not getting the benefits of the fruit's insoluble fiber because the blender completely destroys it. The book also says that not only am I not getting the fruit's full fiber benefit, but also the sugar from the fruit enters my bloodstream just as quickly as fruit juice. Is this true? Should I quit making smoothies? I get two of my daily fruit servings from my smoothie. Is there a better solution? -- K.S.D., via email
DEAR K.S.D.: I don't buy the argument that blending negates the benefits of the fiber in fruits (or vegetables or grains). The machine will most certainly reduce the size of fiber particles, but the fiber is still there. It is the unique way that the fiber molecules are bound together that's the key. Digestive enzymes help break down large compounds into ones small enough to pass through the absorptive surfaces in the intestines. Fiber is unique in that the human body doesn't have any enzymes to break it apart. We do, however, have the enzymes to effectively break down starch into its individual glucose units.
As a result, fiber gets to pass through the small intestine without being absorbed. The blender does indeed cut and shred, but there is no basis to fear that this process breaks down the molecular bonds that form the essence of the fiber.
Blending does effectively increase the viscosity (thickness) of the food as compared with a typical juice or with the product of a juicer, where the fruit's solids are not a part of the final output. Higher viscosity tends to slow the rate at which we eat, as well as the rate at which the stomach empties. Both these factors lead to less food being consumed before you feel full.
Eating fruits, vegetables and whole grains are the heart of what healthful eating is all about. One question associated with smoothies, which you mention, is whether consuming foods in this manner might cause the blood sugar level to rise more rapidly than eating the same foods in the whole, unblended state. The research is somewhat mixed on this matter, and considering the benefit of having these healthful foods in your diet, it makes sense to consider a few more specifics.
What, for example, are the ingredients in your smoothies? You say that you have been consuming fruits this way for a while. Is having smoothies as a regular part of your diet working for you? Do you have any health issues relating to blood sugar regulation? If so, then you should modify the components of your drink.
The great thing about the smoothie concept is the wide variety of wonderful sweet or savory recipes available, including the use of fruits, greens, grains, protein sources and spices (see tinyurl.com/kaduhn7). There are also plentiful recipes for those who want their smoothies strictly vegan (see tinyurl.com/lm4dk7y). As with any food, make it one part of a healthful "big picture." As always, eat slowly and enjoy.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to firstname.lastname@example.org. Due to the volume of mail, personal replies cannot be provided.