That makes sense. I think calories per gram is a reasonably good metric, but there are probably much better ones.

I think the principle still holds: low fat or low carb diets work (when they do) because it is a simple way to help a consumer modify their diet using the lowest hanging fruit based on some reasonable logic (i.e. cut fat 'cuz generally high calories, or cut carbs cuz' Americans generally eat lots of them). You don't have to think about it, and once you form the habit, it's relatively easy to stick to.