Fruits contain fibers that are beneficial for your digestive system and control the spike of sugar level in you body. If you put them in a blender, you destroy much of the fibers and one of the major benefit of eating fruit.
Blending speeds up digestion and reduces satiety versus eating whole fruit, but (unlike juicing) I haven't seen any evidence that it destroys fiber. Do you have a reference?
Apparently the lowered glycemic index for foods
of a smaller particle size is only for starchy
foods (smaller particles hydrolyze easier,
making them higher GI). So while my statement
may have held true for starches, it wouldn't for
fruits. I have no idea about smoothies! It's out
of the scope of the paper, though, so all we can
say is that the study suggests that juicing
increases diabetic risk and whole fruits lower
it.
"Moreover, the process of blending fruit destroys its latticework of insoluble fiber, whose job it is to slow food’s digestion and absorption from the intestine into the blood, explains Robert Lustig, a pediatric endocrinologist at the University of California-San Francisco"
