Mannheim, Germany - If Giulia Enders had not contracted a mysterious illness as a teenager that left her covered with sores, she, like most people, might never have thought much about her digestive tract, except when it was out of whack. She might never have enrolled in medical school either, and she almost certainly would not have written a best-selling book about digestion last year that has captivated Germany, a nation viewed, fairly or not, as exceedingly anal- retentive.

Back in 2007, after a series of mostly ineffective treatments prescribed by doctors, Enders, then 17, decided to take matters into her own hands. Convinced that the illness was somehow associated with her intestines, she pored over gastroenterological research, consumed various probiotic bacterial cultures meant to aid digestion, and tried out mineral supplements.

The experiments worked (although she is not sure which one did the trick), leaving her with healthy skin and a newfound interest in her intestines. "I experienced with my own body that knowledge is power," she writes of the episode in Gut: The Inside Story Of Our Body's Most Underrated Organ, which was published in North America last month after its surprising success in Germany, where it has sold almost 1.5 million copies since its release in March last year.

Inspired by her successful self-experimentation, Enders enrolled in medical school in 2009 at Goethe University Frankfurt and is now working towards a doctoral degree in microbiology there.

Her wonder at the strange ways of the gut is matched only by her incredulity at the limited public knowledge on the subject. "I'm almost shocked," she recalled thinking during her first years in medical school as she learnt, for example, that it is easier to burp lying on your left side than your right because of the position at which the oesophagus connects to the stomach. "Why doesn't everybody know this?"

In 2012, she began taking it upon herself to fill people in. She had heard about a student event space in Freiburg that was hosting a "science slam", an open- mic event where young researchers give presentations, and decided to prepare a short lecture on digestion.

Onstage, she was bouncy and jocular, as a video of the event shows. The crowd was smitten. She 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 Enders for translating abstruse gastroenterological research into breezy, entertaining prose. On a talk show here in 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.

The surprising popularity of her 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.

Enders dismisses such talk, noting that the book has also topped bestseller 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. New York Times