Hi welshrarebit, a tricky one to answer this, fruit contains sugar (fructose) so will increase your bg levels but to what degree larly depends on the type of fruit, the amount of fruit eaten and of course your own individual condition depending on your insulin resistance and pancreatic function.
Fruit smoothies are probably not a good idea as the processing of the fruit makes the sugar hit your blood faster so the increase in bg levels is faster too and probably higher, it is always best to eat food that is as unprocessed as possible that means that your body (intestines) has to do the processing thus slowing down the time it takes to turn the carbs into glucose. Plus It's easy to end up with 3 or 4 pieces of fruit in one smoothie so its like tripling or quadrupling the sugar hit :thumbdown:
Smoothies aside when it comes to fruit the only way to know if you can eat fruit, what fruit and how much fruit is to test your bg before and after eating some and see what it does to your bg levels.
I eat a small green Apple (granny smith) most days with my lunch and a small/medium sized Orange most days after my evening meal as well as the occasional Clementine as a snack and can tolerate these fruits very well but others may find different results.
As an example of amount or portion size I can eat a handful of grapes without a problem, perhaps 6 or 8 grapes but many more will send my bg levels higher than I like to see them rise and I am unfortunately unable to eat grapes in such small quantities, I could eat a whole bunch easily, so I tend to avoid them except on rare occasions where they are perhaps part of a fruit salad where I can just have a small portion that know will be OK for me.
Sorry for the long winded reply.... So to recap fruit smoothies are best avoided by most and all other fruits are best tested to see what effect they have on you as an individual. Oh and generally the less fibre the more sugar so grapes, melon and other watery fruits are generally the worst, for me at least