[katieHaylor (OP)]

Greg asks:

When I exhale, my breath contains carbon atoms. How long ago were they in my food and drink?

What do you think?

[alancalverd]

Could be minutes (sugar, alcohol) or hours (my mum's well-done steak).

[Halc]

Could be decades if burning off stored fat.

[Bored chemist]

With alcohol (or other volatile materials like the sulphur compounds in garlic), it could be seconds

[GregWilson]

Thanks for those responses.

When I asked the original question, I was thinking about carbon making the trip starting with being chewed and swallowed, then digested, entering the bloodstream, powering a muscle, travelling back through the blood to the lungs, then being exhaled.

It sounds like there are plenty of shortcuts possible (like alcohol and garlic being exhaled without making the round trip) and lots of extensions too (like getting stored in fat cells for decades).

If we ignore the short cuts and extensions, and focus on a plain trip that includes powering a muscle, then what's the possible time range?

Thanks,

Greg.

[Bored chemist]

OK, but the unhelpful answer is still "it depends".

For sugars the turn round time could be seconds to minutes.
For fats and proteins it will be a bit longer.
For complex carbohydrates it will be longer still - hours perhaps.

[GregWilson]

Thanks for all that information.

Thanks to the team and the contributors for the terrific answer on the podcast (Episode "Why does dark matter matter?" of 14 May 2019).

Cheers,

Greg.