If you do not urinate out byproducts of cellular metabolism, they still have an equal additive molecualr weight to the original starting components. This is fact plain and simple.
If you lay in be and do not urinate or deficate, the only other way "mass" can actually leave your body is through water vapor evaporation via skin or exhailation.
There is no such thing as a some magical "wierd and complex" process that has "mass" just vanish into thin air. You are being ignorant. BTW, I am using the definition of ignorant as meaning "uninformed" NOT some derogitory definition so please do not take unnecessary offense
The processes by which this can happen have been defined in my previous post.
These are basic principals of science.