or whatever the next fad diet to come along is
It is funny how for every fad diet there are tons of people who say it worked for them. That seems to be proof right there that whatever it is that works must be common to all of the diets. My guess is that simply being on a diet makes people more aware of what they are eating and that consciously or unconsciously causes them to eat less. Some people probably find it easier to do that with a specific type of diet, but the underlying mechanism is still the same.