The people saying "energy" do in fact mean CO2 and water,which are by-products of respiration (ie., literally burning fat). CO2 and water are much more stable a

The people saying "energy" do in fact mean CO2 and water,which are by-products of respiration (ie., literally burning fat). CO2 and water are much more stable and thus you produce energy (heat) as a by-product. Sure, if you're accounting for mass, then yes, by mass the fat turns into the respiration by-products of water and carbon dioxide by the vast majority with a small (miniscule) amount of the mass lost to energy (the rest-mass energy contained in the carbohydrate's chemical bonds are much much smaller than the rest mass energy of the nuclei of the atoms which of course do not transmute).