If you're considering fasting for weight loss it is probably the worst thing you can do for yourself because fasting slows down your metabolism which means you're triggering your body to preserve energy and it will use your fat to keep you going. That in itself is bad because it produces ketones in your urine. If you're hospitalised and they find high ketones in your urine as a diabetic they force you to eat to prevent ketoacidosis which is extremely serious (this can happen for any diabetic on meds or insulin, aka: DKA) It's really bad for your system basically. To lose weight you need to keep your metabolism firing and not slow it down. So it could be that you just need to review your fat & carb intake and see if that needs adjusting to help you lose the weight. But if you're fasting for a test or surgery then you would follow the advice of your endocrinologist or the relevant doc. For me I'm usually told to halve my basal dosage the night before.
Big difference between being an insulin dependent T2 diabetic and otherwise. It's a key difference when it comes to any dietary management of T2D, as far as I understand. Yes absolutely, you need to be medically supervised if you are insulin dependent and considering fasting as a treatment method of your T2D.
Otherwise - dealing with days without food entirely or much less food is a natural part of our physical makeup, and we have the ketones that kick in when fasting to prove it - and is a perfectly natural and healthy part of our physical makeup.
I too was raised with the idea that metabolism is badly affected by fasting and calorie restriction. I am now quite convinced it is otherwise by seeing other's experience, noting my own experience, and reading the science behind the idea that fasting is a natural way to boost your health and good for us particularly as diabetics.
I personally like the metaphor of our bodies being like a dual-fuel engine - that uses both glucose and fat for energy, and we actually switch from one to the other, dependent on how many carbs our body has access to (both immediately accessible as food and in storage in our cells).
But understood even for un-insulin-dependent diabetics being anxious about ketoacidosis. This is where monitoring your fast with BG meter readings, and ketostix (I go budget! But some have a blood ketone reader) comes in. I never engage my poor old diabetic body in any experiment with food and non-food, without paying close attention to it! With BG readings, and now, with regular no-food fasts - with ketostix. (I should be so lucky to worry about my BG going so low! Or my ketones going so high! Sigh.)
As for what to eat and drink
@KimG - there is so much on this online - in this forum included. And Dr Fung has posted very involved fasting for diabetes articles that are quite wonderful. 5:2 diet books - get them out from the library? Until you know you might want to own one of them. Otherwise water only, herb teas, tea and coffee if you are a drug addict like I am! (Hey! Life as a diabetic is hard enough! That's my reasoning and I'm sticking to it.) Making sure you drink plenty of water and liquid so you don't get dehydrated. We don't die of hunger for many many many many days. But we can die from lack of water rather earlier! Just a note.
As for comfort - yep - that differs hugely amongst different folk. I think everyone who has every read me during low calorie dieting (I still can't believe I did that for two whole months - gee!), and then, various fasting, knows I have never been comfortable doing either, and hunger never goes for me. But I would prefer that to taking medications, as that is just a personal preference as to sources of pain!
. And as everyone says - you just need to go for it and try and see for yourself!
And if you are at all anxious - absolutely - be supervised by your medical centre/doctor/diabetes nurse.