The thing I've noticed is that when you've been following IF for a bit you need less food than you used to. I think some people said it was due to you use less calories for digestion than you used to following the multi-meal approach.
Is this weight measurement in comparison to your last weeks weight?
I've been following IF since January and went from 195 to 185 without cutting my calories too much (then with my wifes surgery and stuff the last few months I'm up past 198) I'm back to clean eating now though and losing weight again. I've actually been wondering about the metabolism thing for a while now as my body temp is a little bit lower than it used to be. I don't think I've lost much if any muscle compared to where I was last year at this time.
"And for crying out loud. Don't go into the pain cave. I can't stress this enough. Your Totem Animal won't be in there to help you. You'll be on your own. The Pain Cave is for cowards.
Pain is your companion, don't go hide from it."