Hello, I would like to understand what exactly is meant by "calories" when we read for example that a chocolate bar has 300 kcal. I understand what is a (kilo)calorie. What I do not know is whether the written values are the raw values in calories or if they are the values our body can "extract" from the food. In other words, if I eat the chocolate bar of 300 kcal, can my body use 300 kcal energy entirely taken out from the chocolate bar? Or can my body only extract a lesser quantity than that due to some inefficiency? Another question I have is, say a quarter of a glass filled with oil has also 300 kcal. If I drink it, can I get as many "useful" calories than with the chocolate bar? By useful I mean, can my body use as many calories as with the 300 kcal from the chocolate bar. Or we do "extract/absorb" different food differently? Thank you.