Hello kiwiflyer and welcome to the forum. I am not diabetic thankfully but many past and present posters are. Please click on the FAQ link at the top of the page and scroll to medical conditions. You will find an absolute goldmine of posters experiences and advice. One long lapsed poster WiltUSA was,is? diabetic and was passionate in researching the subject. Can I also suggest, if you are not already aware to research the “Newcastle Diet”. This is a diet developed just up the road from me at Newcastle University for diabetics. Basically it is an 800 cal a day diet for around 8 weeks which has been proven to “reverse” diabetes in many sufferers. Diabetes UK website has more info and it will require medical supervision. This is not a 5:2 type diet but I mention it for info only.
If you are in any doubt about the 5:2 and diabetes please seek medical advice. There are very few “Medical Experts” on this site, including me but we will give honest, truthful and supportive advice to all.
Finally please remember, we are all different, what works for me or you may not work for others but please keep us updated with your journey.
Good Luck.