To the best of my knowledge, there's actually no diet that has been proven to yield long-term weight loss. (There are of course individual success cases.)
There are tons of diets that have been proven to work. Getting people to adhere to them long-term is the problem.
The issue is that people able to keep doing them long term end up in hospitals diagnozed with eating disorders.
As in, inability to keep them long term is biological defense of organism that does not have genetic predisposition toward anorexia.