If, as shown in their energy diagram, all food converts to CO2 and H2O, then no foods can cause weight gain because all the carbon will be exhaled and water exc

If, as shown in their energy diagram, all food converts to CO2 and H2O, then no foods can cause weight gain because all the carbon will be exhaled and water excreted. I read this as an indication that numbers out of a calorimeter don't correspond precisely to the bio-available energy.