Interesting title
Reminds me of calorie density which I wrote about a couple of days ago.
Basically, the average normal eater eats the same volume of food a day. So the same weight of food, to keep their hunger at bay.
If you can chose foods that are low calorie per gram (have a low density), you can get the volume and 'substance' in, and save on the calories
Foods low in density are foods such as fruit and veg, lean protein, high fibre foods. Just what the doctor ordered