I have done the McDonald's diet to prove a point, it does work. Where I only ate from McDonald's over 3 weeks at recomp calories and worked out 3 hours a week, and I still lost 3 pounds while gaining muscle.

It is 'calories in calories out', but you have to actively find what your maintenance calories is over 2 to 3 week periods. So you effectively have to do cycles of cutting and maintenance to maintain an effective loss.

Doing this and keeping 30-40% protein in your meals will have you lose weight doing pretty much anything