When I was lecturing recently to a group of cardiologists at the Mayo Clinic I said...Why is it that from the moment you enter medical school to the moment you retire, the only disorder that you will ever diagnose with a physics textbook is obesity? This is biology folks, it's endocrinology, it's physiology - physics has nothing to do with it. The laws of thermodynamics are always true, the energy balance equation is irrelevant. If someone's getting fatter I guarantee you they're taking more energy than they expend (as long as they're getting heavier). And if they're getting leaner I guarantee they're expending more than they're taking in. [It's] given, let's never discuss it again. And if you say it to your patients you're telling them nothing (University Of Colorado Medical School, May 9th 2013 - via YouTube)