Or ... Stored. Which is the problem.

If we really did eliminate the excess, nobody would be overweight.

No thermodynamics needed to disprove it, but we probably need something more complicated than thermodynamics to get a good picture of the real balance.

Nothing more complicated than a scale in your bathroom is needed. Check daily and see if you lose weight with whatever combination of food/activity/metabolism you have going on. If you somehow gain or lose weight, eat accordingly.

Using the scale is great if you understand proper nutrient timing and partitioning. What if you don't know the basics of nutrition though? Where do I cut from? What can I add in that will assist with satiety but still reduce overall energy absorbed? Where do I go to understand that these are questions that need to be asked in the first place?