Hello and welcome to this SciShow Quick Question where we answer questions the internet asks. The following was asked on my tumblr a while back: "If I weigh 99 pounds and I eat one pound of nachos, am I 1% nacho?" Sounds like not a very complicated question, but it turns out to be, like, super complicated, because buried in this question are a number of other, bigger questions.   First: what is nachos? We can safely say that this is a plate of nachos, invented by the way in Mexico for Americans. It is not a traditional Mexican dish. So this is nachos, and this is me. If I put this, mmmm. Now the nachos are inside of me, but are they still nachos? What about after my digestive system dissolve them into a mushy acidic goo, are they nachos then? I would venture to say, that like if you took what was in my stomach an hour after I ate nachos and put it on a plate, zero people out of 7 billion would call that nachos. However for the sake of argument, let's say that the atoms and molecules that comprise the nachos are still nachos after you masticate and begin to digest them.   In that case the other question is: what is "you"? If I put this ping pong ball in my mouth, is it me now? It is not, it's just a ping pong ball in my mouth. But what if I swallow the ping pong ball, which I will not, by the way, be doing, would it then be part of me? I think we'd get various answers here, but I'm gonna venture to say that no, it's not part of me. Likewise if you weigh 99 pounds and you eat a one pound lump of copper, I'd tend to say that you're not 1% copper. In fact, your digestive system is sort of not inside you, it's just a long complicated tightly controlled tube of outside, that runs through your inside. When embryos first develop, one of the first things they do is punch a hole down the middle spherical cluster of cells, making that cluster a doughnut shape. That middle hole is of course outside the embryo, and that hole becomes the digestive system. But if you take out all the stuff in your digestive system there's a lot of stuff that isn't you, including the several kilograms of bacteria that live inside your gut. By mass, the average human is about 3% gut bacteria.   In the end though, after digestion, about a third of your nachos will never have left your digestive system, and they will be in your feces within a day or two. The rest of the atoms and molecules will be breaking down more slowly to feed you, some of them expelled in your urine and feces, others expelled in the carbon dioxide that you exhale. The truly amazing thing is that by simple virtue of the fact that there are so many atoms and molecules in a single pound of nachos, some of those atoms will remain with you forever, ensuring that you are at least some percent nacho for the rest of your life.   Thank you for watching this SciShow Quick Question, and an extra special thanks to our Subbable subscribers, without whom I would not have been able to answer this question, and how could we have afforded the nachos!? If you have any questions you would like us to answer, we're on Facebook and Twitter and down in the comments below. Don't forget to go to youtube.com/scishow and subscribe.