Taught by a physicist!
Richard Muller, Professor of Physics at UC Berkeley, teaches first:

Want to lose weight? Easy! Just remember the first law of thermodynamics: conservation of energy. Oh, and you’ll have to not mind being hungry.

And, second:

…breathe more. And the only effective way to breathe more is through increased activity.

And, you will probably feel a lot better after a few months of eating less and breathing more.