I suppose upstream is done too, but actually, I think it's usually given nasally ;)
I guess it's simpler and more comfortable that way, you're going downstream so peristalsis and gravity does the work. You don't need to wait with a rather bulky tube up your colon. A thin feeding tube doesn't feel like anything once it's in place.
ETA: wait, did someone actually think they make people eat feces?
He mixed some normal stool with chocolate milk and fed it to the lady.
Related: Son of Low Hanging Fruit
Another post on finding low hanging fruit from Gregory Cochran's and Henry Harpending's blog West Hunter.