[yawaworht1978]

But why not the combination of both?

Losing weight and losing fat is not always the same, a diet with insufficient protein intake might cause muscle loss and thus, decrease metabolic rate(muscle metabolism rate is less than people think, but over a year, it makes a big difference).

However, i understand that not everyone cares about preserving muscle on a diet, some people just want to be slimmer, fair enough.

[slothtrop]

Well there's no reason it has to be "insufficient" and having too little protein is certainly a bad idea. If you consume a source of protein at every meal, whatever the makeup, you can easily hit 16%+ as part of your macros. Even vegetables like broccoli and peas have protein.