Well, I'm not a big guy, but thought I'd share my thoughts with you anyway.

A healthy amount of calories for protein is around 25% of your daily intake. I didn't measure the first few months either, but found out later as I lost more that I have to. I think the key here is to eat normal portion sizes when you still have a lot to lose, but as you get smaller, reduce the portion sizes down as you go. You don't have to worry about that until your weight loss slows down, though. HTH!