A: Remarkably, I could find no studies on what a blender does to fiber. But it's hard to imagine how a machine could do more damage than your molars, stomach acid, and digestive tract. Fiber takes the worst your body can hand out and still manages to help lower your cholesterol, stabilize blood sugar, and keep you regular.
If you're concerned about your smoothies because you've heard that store-bought fruit juice doesn't offer the health benefits of whole fruit, put your mind at ease. It's true, the fiber is often removed from juice. And without the fiber slowing digestion of the sugar in fruit, the juice drives up your blood sugar rapidly. This can contribute to insulin resistance, a precursor to diabetes. But a smoothie made with whole fruit still has fiber.
There is one other factor to consider, however—smoothies go down your gullet much faster than a piece of fruit. And research shows that we don't register liquid calories as accurately as food we've chewed. So fresh, unpulverized fruit gets the upper hand. But just barely; enjoy that smoothie.