Dr. Jason Fung.
A good overview why reducing calories + more exercise stops working after the initial few months.

Uses a great example of how all contestants from The Biggest Loser TV show gain all their weight back after the initial 6 months.

The Biggest Loser is the perfect example of the mainstream diet advice - eat small portions often, create caloric deficit, eat balanced meals - plants and lean meat, do lots of exercise.

If literally 100% of the Biggest Loser contestans fail even though they have all this amazing support/motivation and even huge financial incentives to keep the weight off, then you are guaranteed to fail on any diet that focuses on cutting calories (eating lots of small meals) and exercise.

That has been the default medical advice for the past 30-50 years - create negative caloric state by eating less (to create caloric deficit) and by exercising more (to create caloric expenditure).

The result of this default medical advice is where we are today.