Hi joshy:

Most of the weight you lost was water weight from the glycogen being released from you liver. You may have another week or so of above average loss, but it is not harmful.

After your initial, quick, losses, you will probably experience a ‘plateau’, where you lose little weight for up to a month. Sometime during that period you might even gain a bit of weight. Again, all normal.

Overall, the average weight loss over time with 5:2 is about a pound a week. You can see how the ‘plateau’ works to get you to that kind of an average – say 8 pounds the first two weeks and nothing for 3 or 4 brings down the average to a more realistic rate of loss level. The only way an average overweight person can really lose three or four pounds of fat a week is to eat nothing at all for weeks on end.

If you are very overweight, that means your TDEE is quite high and you have a better chance of losing more than a pound a week, on average, until your weight drops some, at which point your rate of weight loss will start to decline from, say, a couple of pounds a week to a pound and a half to a pound, etc. The key is to just keep going and not worry about either the rate of loss or the consistency of loss.

Here are some tips for those just starting 5:2: https://thefastdiet.co.uk/forums/topic/the-basics-for-newbies-your-questions-answered/

Good Luck!