wouldn't that be a great experiment though, really? Do do 1500 calories of crap for a month - then 1500 calories of good stuff. For me, the important thing is that I feel so much more energetic and better mood on healthier food so I'm not sure it would matter. I'm not just in it for weight loss - I'm in for fitness factor! I suspect one would lose better on healthier foods but that would shoot the calories in versus out theory. Who volunteers for the study? You'd have to make sure all other factors remained exactly the same (exercise level, amount of water, amount of sleep...etc). We could make money and write a book.
Oh it's been done!
The logic is that as a short term diet - the most important thing is to lose the excess weight and all its bad health implications. So a professor went on a 'doughnut only diet' He still restricted his calories, but ate only doughnuts! Lost the unhealthy weight. Caories in = calories out.
Of course long term he was depriving himself of important nutrician; but he argues that by fat the most important thing is to lose the weight in the first place