I've a question I've never seen addressed. It's likely that some of what you consume is actually utilized ... and that some, if it's not needed, is just 'ignore

I've a question I've never seen addressed. It's likely that some of what you consume is actually utilized ... and that some, if it's not needed, is just 'ignored' (excreted). Oxygen needed? Very little. Also some people can eat and eat, whatever they want, and not gain a lot of weight. Genetics has to be part of it.