Weight / Fat loss

That line could sum up the whole field.
It is an area crying out for some good research.
Sadly there are almost too many confounders for any real sense to be made of the results when they occur.

People confusing cause and effect all day long. The only thing that matters is creating a calorie deficit. Eat well, but restrict what you eat, or, like me, face up to the fact that the only way to do that on top of the already healthy diet, is to cut out the booze for a while. Add in HIT cardio and resistance training.

5:2 can create an unhealthy relationship with food/disordered eating.