Personal trainers, exercise regimes, meal replacements, slimming clubs, books, videos, calorie counting, diet plans......
It's all a multimillion pound industry and people over complicating it.
Exercise is great to keep you fit, but it's intake reduction which will be effective to losing weight.
There weren't any fat blokes in prisoner of war camps.
But we're keeping on reinventing the wheel and changing the name, and people are making fortunes selling books etc.:
Atkins diet, Keto diet, Avoiding diabetes diet etc.
Years ago we called it the bread and spuds diet, and it worked.
Of course now it would have to be called the bread, spuds, rice and pasta diet.
Keep it simple:
Cut out the obvious sweets, cakes, biscuits, beer etc, and reduce your input of carbs.
Plenty of protein and don't get too anxious about the fats, and drink plenty of water.
It's worked for me, and my weight and waist size has stayed within recommended levels for my height well into my 80s.