1200/day is a deficit. It will make you lose a lot of weight. Most people can take it, but not indefinitely. After you've lost all fat weight, normal muscles atrophy, then vital organs are consumed and fail.
It's a crash diet. Not healthy in short or long term, but something people do when desperate to get an effect.
To some, this is a tragedy and societal problem. To TOM FUCKING ELLIS it is a market to validate and push products to.