So maybe he's eating other, 'healthy' things that you don't know about. Who knows....
My point is and always will be, until something exists that suggests otherwise, that there has never been a documented case (and there's a lot of studies/cases) where you put someone on a clinically controlled diet and they didn't lose weight. Period.
Thermodynamics always win.
That said, Mal is correct in saying that it's stupid to base all progress on the number on the scale. With that though, when you have as much weight to lose as he does, the scale should be falling, especially considering the intake.
I highly suggest you start taking measurements of the neck, arms, belly button, waist, hips, and thighs. I also suggest taking pictures.
All this said..... if he doesn't buy into the lifestyle mentality, he will fail.
Read that again.
The diet mentality never works. And my definition of 'works' is losing weight permanently. If you view this as a temporary endeavor and base all success on the scale reading, what happens when the scale spits back with the goal number?
Do you really think it will stay there?
He already proved it himself, when he gained all the weight he lost, back.
If I've said it once, I've said it a dozen times..... if you don't change the brain, you ain't gonna change the body. At least not permanently. How we think leads to how we live. This is a known fact. By changing how we think on a chronic level, we actually directly change the chemistry of the brain. You re-wire or re-program yourself to feel and behave differently.
Without this step, it's a fruitless endeavor in my opinion. Doing things without this step (and I don't like calling it a step, I should be saying without this component of programming) all efforts tend to lead to unhealthy habits and frustrations IME.