Gastroenterology: Down the hatch

David Katz savours a guided tour of the ins and outs of the gastrointestinal tract.

Gulp: Adventures on the Alimentary Canal

978-0393081572 W. W. Norton/Oneworld: 2013. 352 pp. $26.95, £11.99 978-0393081572

A singular recollection came to me as I began the adventure of Gulp. I used to teach a course called 'Clinical Concepts in Public Health' at the Yale School of Public Health in New Haven, Connecticut. This was my opportunity to convey to bright young graduate students the marvels of the human body in both function and dysfunction. It was an epiphany. Compressing the greatest hits of medical education into a single semester helped me to fully appreciate how truly astounding it all was.

Credit: SCIEPRO/SPL

My impression is that Mary Roach experienced her guided tour of the gastrointestinal tract in much the same way. There is a real sense that her mind boggled at its wonders. In her blend of excellent investigative journalism, history, popular science and stand-up comedy, you are in for diverting surprises: don't expect this book to be a straight shot from the northern to the southern orifice. Each port of call along the way is more an excuse for fascinating detours than a destination in its own right.

We learn, for instance, about the work of some of the world's more specialized and surprising scientists, past and present. One has devoted a career to studying what causes variance in the odours of flatulence; another researches the secrets of saliva, such as what makes it flow. We learn about a scientist who pushed a live eel through a fistula — a surgically created hole — in a dog's stomach, so that only the eel's head protruded, to determine the extent to which animation upsets the actions of digestive juices. The answer proved to be: not at all. The eel was digested; the scientist, divorced.

We learn how snakes digest prey they have swallowed whole (through extremely powerful enzymes) and the likely cause of Elvis Presley's death (Hirschsprung's disease, or toxic megacolon). Roach reveals why the various worm species that are swallowed alive by reptiles and amphibians cannot eat their way back out. We are told the possible origins of the myth of fire-breathing dragons (hint: it has to do with decomposing mammals in the guts of large snakes, in proximity to Stone Age campfires).

In Gulp, Roach imparts her myriad insights eloquently, and with acerbic wit. A dog's nose “takes in the sights by smell”, and “it takes approximately as long to chew narwhal as it does to hunt them”. She regales us with prime examples of nominative determinism: a scientist named Spitz studies saliva; one called Grime researches laundry detergents.

Adroitly avoiding squeamishness, Roach reveals the coda to this story — the anus — as a remarkable orifice. She shows how sensitive it has to be to differentiate solid, liquid and gas, and to perform its yeoman's work accordingly. As Robert Rosenbluth, a medic she quotes, puts it: “No engineer could design something as multifunctional and fine-tuned as an anus. To call someone an asshole is really bragging him up.” (Personally, I find that statement smacks of a slight excess of enthusiasm, and take umbrage on behalf of my kidneys and liver, to say nothing of my brain.)

The last chapter addresses the gut's role in autoimmunity, and discusses the potential therapeutic value of 'fecal transplants' in treating colitis caused by the bacterium Clostridium difficile. A promising approach to a difficult problem, Roach tells us, assuming we can get past the 'ick factor'.

If there is anything at all unpalatable here, it may be the relative paucity of practical information. If something ails your innards, Gulp is unlikely to help. There is nothing remedial, therapeutic or prescriptive on the menu here — but Roach has made no promises to offer them. Her food for thought is proffered purely in the service of entertaining enlightenment. Roach lays out the acts of ingestion, digestion and egestion, all incisively chewed over — with tongue ever in cheek. How she does so without once biting that tongue is a testament to her authorial gifts.

Another memory surfaced as I completed the journey along this extraordinary canal. Some 20 years ago, during my medical residency, I wrote a skit for an annual roast of our attending physicians. There were several well-loved gastroenterologists among the teaching faculty, and I lampooned their avid enthusiasm for all things gastrointestinal by asserting that they were, on the side, producing the world's first science-fiction movie filmed entirely through a colonoscope: There's Life on Uranus! It's a film Roach might have directed.

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Correspondence to David Katz.

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Katz, D. Gastroenterology: Down the hatch. Nature 495, 446 (2013). https://doi.org/10.1038/495446a

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