> But, no one has ever put on weight on a calorie deficit. NEVER.

The vast majority of people who lose a substantial amount of weight through calorie restriction gain it all back and then some within a few years. Though they do lose in the short run (say, 6 months), they're worse off three years later than if they had never dieted at all. This simple fact - that dieting doesn't work in the long run - suggests that telling people to lose weight simply by dieting is BAD ADVICE.

Given that doctors are giving people bad advice, there's still plenty of room for people to try to come up with BETTER advice.