Dear me. Hasn't anyone spotted the obvious? It doesn't matter what % of methane, etc. Once the mass of the fart, whatever its composition, has been expelled from the body, you are lighter. Basic science, people...

(P.S. I just skipped half the thread because you were all so obviously talking utter nonsense as is normal for the 'Cat. ;-) So apologies if someone diid latterly say this...)