Honest question - how good a fit / approximation is the concept of a calorie (as in, we burn the material in question, and measure energy given off as heat) in approximating the energy extracted from the material through digestion?
Obviously the laws of thermodynamics hold, but I find the above equality to be slightly presumptuous - an obvious exception is that "fiber" can be burnt, but not digested (by humans, at least). What other caveats are there to this system, and are they employed to adjust calorie numbers for foodstuffs? I'm genuinely curious to know more about this, are there any good, concise sources?
Thermodynamics are mostly useless when you look at nutrition, even if they are true. The same amount of calories from different sources get metabolized differently, have different effects on satiety, insulin, and a whole host of other factors. Nutrition is biochemistry, not physics.
Sure, you will lose weight if you reduce calories. But that information is about as useful as general relativity when you want to throw a ball to another player.
Obviously the laws of thermodynamics hold, but I find the above equality to be slightly presumptuous - an obvious exception is that "fiber" can be burnt, but not digested (by humans, at least). What other caveats are there to this system, and are they employed to adjust calorie numbers for foodstuffs? I'm genuinely curious to know more about this, are there any good, concise sources?