system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If our bodies can’t break down certain foods like celery and corn, how do we get nutrients from them?
gpt
Well, it's not that we can't break them down, we just can't digest the cellulose that makes up much of their structure. Not to be gross, but it's common to see "intact" corn kernels in stool. However, if you were to take that kernel and cut it open, you'd find that much of the inside has been digested - it's just the cellulose that remains. Celery is a bit denser. We can't really digest much from it, so we get only a few measly calories from celery. That's why some people say that it takes more calories to digest celery than it provides, but such claims should be taken with a grain of salt because in reality, metabolism is more complicated than that.