Might want to check up on this. http://en.wikipedia.org/wiki/Negative_calorie_food

That's very interesting

The thing is, the digestion calories are one small portion of the dietary effects of any food.

For example, some increase thermogenesis, so you could account for that

Yes, apart from cold water it seems hard to think any food can provide no calories. Evolution took care of our digestive tract extracting the most of food (unless you're eating paper)

I'm certain that apples do not fall into the negative calorie category of celery, cress, etc. but it's still a possible answer to the "what model" question, so thanks. I guess that's what "Filligree" was going for...

Apples and other fruits are full of fructose (sugar). How the hell are people suggesting that they take more calories to digest than they contain?

Disregarding biology, an apple has .15 kg * (c^2) -> cal = 3.2 × 10^15 calories