[dennis_jeeves]

>Would you say it's just a matter of calories in minus calories out?

Strictly speaking , yes, Otherwise, no it is not. If one were to really calculate calories in/out that would be really complicated: you have to consider many factors for example energy required to digest food, energy extracted from the food, energy lost as body heat etc. as far as I vaguely recollect, even something like body heat burns more calories that vigorous exercise.

In general the calorie obsession is nonsense. Just because some scientific sounding jargon is thrown in does not make it well thought off. On a 'good' diet most people will never have to count the calories. Again the takeaway should be that you can fool most people, most of the time. Treat any subject that has popular endorsement with skepticism.