Energy can not be created or destroyed, it can only transfer forms. The first law of thermodynamics tells us the higher a roller coaster climbs the faster we go.
That's an enjoyable aspect of the law. The not so enjoyable finding is what it means for our eating.
It also tells us the chemical energy or CALORIES we take in as food must either be used to do work or stored as fat.
The plethora of new diet strategies that come out every year is a testimony to the power of this first law and the futility of trying to avoid it.