In reply to ffati:
Did the 5:2 for a while and found I was fine climbing on the days fasted. I climbed in the mornings to early afternoon. For me fasting days meant limited calories rather than full fast and I would eat after climbing. Once I started climbing I was fine because vigorous exercise always seems like an appetite suppressant for me.
I don't think you have to be particularly strict about the amount of calories either IF you're just having one meal. Just don't purposely overeat or eat junk. I found a normal meal satiating enough. I did get hungry in the evenings so it took a bit of will power (and a few hot drinks).
Getting a decent amount of fat in your diet too I think helps. It makes you feel fuller and for longer. It's carbs that cause blood sugar spikes and crashes. From what I've read intermittent fasting and high fat/low carb diets work well together because they're basically doing the same, or a very similar thing.
Another variant is the 16:8, ie. fast for 16 hours out of each day. When/if you finish with 5:2 this is a good successor to follow. Definitely easier but positive results too according to a recent study:
https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-01...
I found the fasting diet really helped me tune in to when I was properly hungry rather than just the expectant hunger you tend to have at every meal time.