5/2 is not a ketogenic diet unless you want it to be. A lot of people find limiting carbs, or not eating at all on fast days, helps limit hunger pangs but those are personal preferences not a requirement of 5/2.

No, you will only switch over to burning ketone bodies if you eat just a couple of protein items and green vegetables with oil, (very little fruit) on non-fasting days. However, you can allow yourself one pleasure, a glass of dry white or red wine with your two meals on those days. The fasting days should really be water and black coffee only (or broth).

Decided to do an experiment, since I’m doing a contract in Aus & am not busy on the weekends.
Friday did a normal FD, low carb. 2 boiled eggs breakfast, stir fried steak with cabbage, zuccini, spinach for dinner – 600 kcal for the day. Yesterday, total fast – lots of coffee, herbal tea, water. Urine strips indicate that I was in moderate ketosis mid-afternoon. Optimal ketosis range this morning. I’m planning on breaking the fast at dinner (48 hr total)- BBQ leg of lamb, Greek salad & oven roast rosemerry potatos (& red wine of course). I have tried low carb eating prior to this & it took 2-3 days to get to moderate ketosis. First time I tried with a total fast – kicked in fairly fast & first time I registered optimal ketosis in the morning.
Did my normal workouts + some long walks the past 2 days, no issues. See how it goes this morning. No hunger pangs at all, but I do have a bit of a dull headache – more of a dull pressure than a real headache. Only about 5 hrs sleep so will likely need a nap after the gym.