Back in my Green Smoothie Phase (oh, those were happy days...) I was always delighted at how small a blood glucose rise I got from the smoothies. I use(d) a Vitamix, so it was whole fruit/veg, blitzed to a velvet smoothness, rather than extracted juice, or roughly mashed fruit. And I used yoghurt or water as the liquid instead of some sickly processed fruit juice. And sometimes I added psyllium husks to give a gloupier texture, more fibre and slower carb release.
The thing about green smoothies (which are a combination of fruit and veg), is to get the flavour of the fruit and the benefits of the veg, and you get to design your own smoothie. The often quoted figure for a good balance is 60% veg, and 40% fruit, but of course you can tweak that to your heart's content. Less fruit, or less sweet fruit, more mild tasting veg (like courgettes) = less sugar. Even blitzed fibre does a good job at slowing bg spikes. Maybe because the soluble fibre is already in solution and doing its job?
And if you add nuts like cashew or macadamia, and count avocado in your fruit %s, you can increase the healthy fat content while simultaneously slowing the digestion and the speed that carbs hit the bloodstream.
There is a lot tweaking that can be done, to make sure that the smoothie doesn't hit the bloodstream like an express train.
