This is the key. People who go on diets eventually go off their diets and go back to their old habits. BJJ is a new way of life, so as long as you stick with it and don't actually eat more than you did before, you're going to lose weight and keep it off.
I've been on my "diet" (live-it) for about 4-5 months now.
I had to lose weight for a lot of reasons, but the important ones are my wife and daughters.
Being able to go to the amusement park and be able to fit on the rides was a breath of fresh air.
I've been fighting this last 7 pounds of my halfway point goal for 2 months now. Normally I'd have given up a month ago but I havent this time. I'm proud of myself so far and I will throw myself a little party or something when I finally break that halfway point (buy a new gi, perhaps).
But I'm really getting into BJJ, and my daughter (7) took her first class yesterday. The intructor said he'd prefer to get her into a Gi and away from the other kids her age because she's more mature and already has some skills (we kickbox together all the time on the bag).
I was smiling ear to ear - when they were warming up and just doing some general self defense stuff and punching etc to get it out of the kids system he said "come on Sarah, let's see what you've got - do two punches and that kick I showed you"
She takes a regular boxing stance, hands in the right position and throws a jab/cross and then a "front kick" as he called it - breathing with each strike. He asks her what she did and she says "I put my guard up, did a jab then a cross and then a thip kick"
He's one of my instructors too, but he just looks over at me with that "hell yeah" kind of look.
Couldn't have been more proud, I don't want her developing the same bad habits I did at a young age that led to me getting fat.