Is it time to rethink calories?

To a physical scientist it would seem quite simple. A calorie is a unit of energy. It is the amount of heat energy required to raise the temperature of 1 gram of water by 1 degree Celsius.

This was adopted with gusto by the early biologists in their understanding of energetics. 

According to the second law of thermodynamics, energy is neither gained nor lost, it just changes form. Hence, energy taken in, in the form of calories (in food or drink), needs to be balanced by energy expended (by physical activity, heat loss or