I don't think this is true. According to this table a large apple has more than 100 calories: http://calorielab.com/foods/apples/62

Erm...what? I don't understand. Calorie-per-dollar ratio = p/q for p calories and q dollars. What model are you using where p or q but not both is negative for the apples example but not the BigMac one?

Have you ever eaten a dollar? Those things just don't fill you up.

Hahaha, "for p calories [in the food] and q dollars [cost of the food]" is supposed to be implied but I like your quip!

To digest an apple it takes calories. Yes, an apple has around 100 calories (depends on size) but the net value can be negative.

Celery is the classical example of this.

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

How can it be negative? Do you mean less than 1?