> what percent of molecules in the body aren’t involved in biology. The answer to that is probably something that approximates 0%. I think the answer might be

> what percent of molecules in the body aren’t involved in biology. The answer to that is probably something that approximates 0%. I think the answer might be different (and more interesting) if constrained to human biology. What percentage of the variety of “stuff” in our bloodstream/tissues, that came in from our air/water/food and then maybe got metabolized a bit, is now of a form entirely inapplicable to anything going on — or that could even potentially go on — in a human body? How much is pure “waste to be excreted” from the human perspective, with both no use in keeping it around, but also no danger in keeping it around? (I know that this is at least what allantoin is for the species that make it; but we’re not one of those.) I presume a lot of toxins that get inactivated by the liver end up in such a form.