If it’s lighter than air, it’s lifting you while it’s inside of you…

If it’s not there, it’s not lifting you, and you’re heavier.

Think of a balloon that is so old it doesn’t rise anymore. It just stays neutrally bouyant. In this case it’s even less than that. It is a completely and totally negligible amount of difference. But while holding a fart you’re technically a very shitty balloon.