A calorie is a measure of energy equal to around 4.2 joules, and it is not necessarily thermal energy, however the thermal energy in a unit of energy can be measured by change in temperature. You could also measure energy by calculating Newton-meters. A food calorie is equivalent to a kilocalorie which has enough energy to raise a kilogram of water by one degree C. Good nutrition is important, but eating the right amount of calories to provide your body with energy is equally important
I understand what a food calorie is, but that still doesn't explain what a calorie has to do with nutrition? If it's in reference to food providing "fuel" for the body (i.e. burning to make heat, like oil) then how do you explain "good" calories and "bad" calories??
We know that 1000 calories from a couple of beers, does the body ALOT more damage than 1000 calories coming from a whole bunch of apples. They both supply the same amount of "energy" but one will make the body fat and lethargic, and one will make you lean and vigorous.
I don't know how much "faith" one should put in the caloric system.
Want to know how much to eat?? listen to your body!! it will tell you when you need to eat more food! that's what HUNGER is! it's your body signalling that you need FUEL!