It is calories in/out but having guardrails is super helpful to a lot of people. Many overweight people got that way because they run pretty loose ships when it comes to diet to begin with. Rules can be helpful. Intermittent fasting of course is pretty popular and followers seem to get results.

Couple years ago I lost a bunch of weight just following “Eat Right for Your Blood Type” which I’m sure is quackery- but it was effective. Felt great too.