I used to make green smoothies regularly.
They were no problem for the blood glucose at all (I don’t use tablets or insulin to control my blood glucose, so have to do it by dietary control).
The excellent thing about green smoothies is that tailor them to your own personal requirements, and can change any ingredient depending on fibre, carb and flavour, to create whatever smoothie you like.
The general idea is less than 40% fruit (flavour and sweetness), more than 60% mild tasting veg, and a liquid.
To make it low carb, simply select low carb fruit like berries, and a low carb liquid, like water instead of fruit juice.
Favourite recipes of mine were
Spinach
Courgette
Avocado
Water
Berries
Cashew nuts
Or
Baby kale
Celery
Cucumber
Water
Pear
Ginger
Half a lemon
I also did a fab Black Forest Gateau smoothie with
Lettuce or salad greens
Courgette
Half an apple
Frozen black cherries (not many)
Cashews or macademias
Cocoa powder
Please note that these are whole veg pulp smoothies with masses of fibre, not sweet tropical fruit sugar dumps.
I can never understand how people make sweeping generalisations about ‘smoothies’ causing high blood glucose ‘spikes’.
The reality is that any one of us can put together an excellent smoothie, packed full of nutrition, flavour and freshness, without causing any untoward blood glucose impact. Its easy. It just takes a bit of practice, the correct balance of ingredients, and not drinking it by the bucket full.