Without any other information I would guess that you’re eating too many calories on the non-fasted days. You still need to keep track of the amount of calories per day and end up in a deficit over the course of the week.
I do 5:2, Mon and Thurs as well. I haven’t noticed a difference in weight loss if I eat 500-600/day or if I eat nothing at all. Zero difference in weight.. but a big difference in my mood. I’ve noticed a HUGE difference if I get in a good fasted workout (just running ~1 mile). Working out on an empty stomach has been the key to my weight loss. Even if I have a 500 cal day and have a spinach-shake for lunch, and then work out, at best it’s a flat day… no loss.
The biggest challenge is the other 5 days.. it’s too easy to go back to the bad eating habits.
In general, here’s my schedule:
I’m not a fan of 5:2. It’s kind of outdated now, and the 500 cal for the two “fasting” days is dumb and more likely to stall you out than doing a real fast on those days. It’s too easy to overeat and eat all day long on the other 5 days. Eating a small amount actually makes you hungrier than eating nothing at all.
Instead, you should do daily fasting (I recommend OMAD, but do 16:8 at minimum) and maybe do a 48 each week or two 36-40 hour fasts. You will definitely see results then.
5:2 + skipping all breakfasts did amazing things for my dad the year he retired. He was pretty close to ripped in the end lol.
So yeah, I would probably try to at least do 16:8 on those ‘eating days’. If so, should work really well.