The crowd was smitten. Ms. Enders won the competition and went on to participate in two more science slams in Karlsruhe and Berlin. Soon, videos of her presentations were attracting attention online, and a literary agent contacted her about writing a book.

FANS have praised Ms. Enders for translating abstruse gastroenterological research into breezy, entertaining prose. On a talk show here last April, she described the large intestine as the “chiller” of the two because it processes nutrients at a leisurely pace of about 16 hours on average, compared with the two to five hours that the small intestine needs.

In her book, she catalogs the myriad elaborate operations that our guts dutifully perform every day, like the cleaning mechanism that kicks in a few hours after we eat and keeps the small intestine — all 20 or so feet of it — remarkably tidy. This “little housekeeper,” as Ms. Enders calls it, turns out to be the real source of the grumbling that most attribute to the stomach and mistake as a sign of hunger.

Then there is the growing body of research indicating that our intestines may have a far greater influence on our feelings, decisions and behavior than previously realized. The primary evidence for this, Ms. Enders writes, is the vast network of nerves attached to our guts that monitors our deepest internal experiences and sends information to the brain, including to those regions responsible for self-awareness, memory and even morality.

Just how much your lunch will affect ethical decision making remains unclear; we still know very little about this “gut brain,” as Ms. Enders refers to it. But this byzantine neural architecture suggests that our intestines may play a large part in determining who we are and what we do.

These essential but little-known features of our guts — our identities at their most raw and visceral, Ms. Enders suggests — have riveted Germans. The surprising popularity of Ms. Enders’s book has itself become a topic for discussion, with some commentators invoking Freud to explain Germans’ apparent fascination with their bowels. Profanity here tends to skew to the scatological, and Germans are, according to stereotypes, obsessed with order and neatness.

Ms. Enders dismisses such talk, noting that the book has also topped best-seller lists in Finland, the Netherlands and elsewhere. She suggests that its appeal lies in its frank treatment of topics usually left undiscussed. “Shame always disappears when you really understand something,” she said.