Nutrition Professor said:
"I wish I could say the outcomes are unhealthy. I wish I could say it's healthy. I'm not confident enough in doing that. That frustrates a lot of people. One side says it's irresponsible. It is unhealthy, but the data doesn't say that."
Data doesn't say that? data doesn't say what happens with long term habitual 500-800 daily calorie deficits.
Calories in/out definitely works but if you're drastically reducing calorie...