Everything we consume eventually comes back out, and in other ways besides the most obvious. Many of the foods we eat are excreted through the skin via sweat, and lends itself to the many smells of body odor.
On a side note, the author can smell poison ivy being metabolized in his own body and excreted in this way. I can also tell the quality and type of milk product within 20 minutes after consumption - I might not notice "old butter" while I'm eating it on my toast, but I'll know soon enough. Gross. Milk smells not-so-much, and pizza cheese is the worst. I have a hard time finding people who know what I'm talking about, so if you do, please comment(!).
On transformative human effluence:
Scientist Christina Agapakis and olfactory artist Sissel Tolaas acquired and fermented human sweat to make cheese out of it. The big deal was the cheese made from Michael Pollan's stomach sweat (totally edible, even for vegans!).
And on the topic of disturbing performances:
Olivier de Sagazan's "Office Man", in the 2011 film Samsara, by Ron Fricke and Mark Magidson