Some basic myth busting facts.
The laws of thermodynamics dictates it is always calories in V calories out for weightloss. The problem is that it is next to impossible to track exactly what goes in and what goes out.
Metabolism can slow but not much or people starving wouldn’t lose weight! Undereating does not make you fat, eating too much for your own activity levels does.
All calories are equal but the body may use more energy processing some.
Extra calories always ends up as fat. Fat is used as required then stored, protein is used as required then converted into sugar, carbs are used as required, including stored as liver glycogen, spare is turned into fat.
There has been evidence that the brain changes signals and pathways if you eat high processed food, meaning you can overeat, eat 2000kcals of good quality food, you’re full. Eat 2000kcals of shit your brain tells the body it wants more.
Most “diets” work because they get people thinking about real food and cutting snacks. Most “diets” are unsustainable in the long term. It’s all about habit changing
This is oversimplified and taking away all the mineral and vitamin requirements for a healthy body and not taking athletic lifestyles into account.