> you can't gain more weight than the weight of the food you eat, because conservation of mass Not, strictly speaking, true: not only must we consider mass-ene

> you can't gain more weight than the weight of the food you eat, because conservation of mass Not, strictly speaking, true: not only must we consider mass-energy equivalence (the chemicals bonds in food vs metabolic byproducts could contribute unequally to mass), but more importantly, we inhale mass well as ingest. From the article, one mass-unit of inhaled oxygen produces less than one unit of exhaled carbon dioxide (although I suspect that more than enough water is lost though net exhalation alone to make up for it). So we have to be a little careful with this conservation of mass argument. It's still basically correct, though, and more-or-less blows the "weight gain is exactly proportional to excess calories" argument out of the water.