You are what you eat

For an easy example of why E=MC2 is true, consider food. A solid of some sort, or perhaps a liquid, but hardly ever a gas, is consumed, by you, and your body - a cunning machine - converts this matter into energy, which we measure in units called calories. We use this energy to operate the very machine that converted the matter into energy in the first place. Hmm. To what end, one wonders....