Having done 28 days of the potato diet, this is true. It is difficult to get over 1kcal of potato. Eating two kilos of potato in a day is heroic. I would eat like 1 kilo per day, and be satisfied-full. It's wild.
One can eat 2 kilograms of boiled potatoes, refrigerated, cut into very thin slices and then air-fried at 400F for 15-20 minutes with a drizzle of avocado or extra-virgin olive oil. Some rosemary too.
An overall increase of about 150 calories per kilogram compared to boiled potatoes only.
The flavor is similar to that of French fries and they are an excellent substitute (I say this as someone who when asked what would be his last meal would answer: french fries).
Calorie density is not something made up. You are redefining a very well-known term. Many legumes, grains, and root vegetables are made up of copious amounts of water in their prepared form.
Calorie density is also not the only metric for recommendation. Everyone agrees that liquid calories are not "felt" by the body in the same way as solid foods.
