I currently fast twice a week (Mon & Fri) in such a way that I don't eat any solid food; I just drink lots of water, green tea, black coffee and one mug of broth (homemade, or from a Kallo stock cube). I built up to this through 5:2 when I was eating a 500 cal meal on a fast day, but I found it so easy (thanks to LCHF and being in ketosis) that I decided to try not eating at all. There are many other ways of fasting, including a timed period like 16:8, where you eat all your meals within an 8-hour window. Another possibility is not eating for a stretch of 3-4 days on a monthly basis - I understand that is what
@AloeSvea does.
Why I do it? To heal my T2D and get rid of excess fat. Here's a post that explains a little about it:
https://intensivedietarymanagement.com/fasting-cures-diabetes-t2d-4/ but there is a whole series of fasting posts on that site that give a fuller picture. The diabetes and obesity series are also eye-opening.
I have not been prescribed any medication, so if I want to not develop complications further along, I have to control my diabetes through my behaviour, mostly eating. LCHF was a great start, it helped me reduce my HbA1C fro 49 to 36, and my weight from the BMI of 40 to 34. With added fasting, my FBG has reduced from 6+ to around 5, and I'm solidly shedding fat - at 30.5 BMI now. I imagine that when I reach some kind of normal weight (I'm not sure what it is, as I've been overweight and obese my whole adult life) I will reduce my fasting to some kind of maintenance - maybe one day per week of 500 cals. But there is evidence that fasting is good for all sorts of health outcomes in addition to weight and glucose management - blood pressure, autoimune diseases and longevity are also positively affected, so I plan to continue some form of fasting for life (The Fast Diet by Michael Mosley explains more as well).
I hope I've managed to explain what I do and why, but feel free to ask more questions!