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A Brief Tour Of The Alimentary Canal, From Spit To You Know What

There's a lot more going on in our guts than just digestion.
Andreas Lindlahr
There's a lot more going on in our guts than just digestion.

Not so long ago, the workings of the digestive system were of interest only to gastroenterologists and 10-year-old boys. But the gut is now chic, with its microbiome playing a huge role in human health, and passing gas deemed a sign of healthy gut microbes.

What better time to take a tour of the alimentary canal with Mary Roach? Her latest book, Gulp, just came out in paperback, and we figure that's reason enough to chat up the science writer who has proven to be an enterprising chronicler of sex, death and the afterlife. Here's an edited version of our conversation.

I was surprised to learn that spit makes a great laundry spot remover, and even more surprised to learn that art conservators use it to clean paintings. How did you find that out?

That may have been something that I found once I learned that saliva has this enzyme that breaks down starch. These are the same enzymes that are in laundry detergents. To be sure, I called up the American Cleaning Institute, formerly known as the Soap and Detergent Association. They referred me to a guy named Dr. Spitz. He didn't know, so they referred me to a guy named Keith Grime. I love that. Anyway, he confirmed that it's the same enzyme, amylase. I asked him, 'Do you dab a little saliva when you drop food on your lap?' He said, 'No, I use a Tide pen'. But I do. I had already been using saliva as a handy presoak, even though I didn't know why it would work. I should have my own little 'Hints from Mary' column.

What about the question that grade-school boys have pondered for all eternity: If I eat too much will my stomach explode?

It is hard to rupture the human stomach, but the best way to do it is with bicarbonate of soda. It creates this rapid release of gas, which pushes your stomach over the breaking point. In a historical roundup of ruptured stomachs, far more of them were from bicarbonate of soda, the thing, ironically, that you took to make yourself feel better after overeating.

Moving further down the digestive system, you taught me way more than I ever thought I would know about how people smuggle contraband into penal institutions: the "prison wallet". How did you research that?

It was an interesting afternoon. I called up the California Department of Corrections and Rehabilitation and got the public affairs guy, who said: 'We've got a problem with rectal cellphone smuggling. I'm sure we can set something up for you.'

I thought I'd be talking with the guards, but I sat in a room with a convicted murderer and we had a conversation about his rectum. That's how my day went.

In recent years we've learned that the bacteria in fecal matter can actually be life-saving for people with serious infections. You observed the transplant process. How does it work?

I spent time in Minneapolis with Dr. Alex Khoruts, who for a long time has been involved with fecal transplants. The more tidy term is bacterial therapy. A donor, a person with a healthy gut, shows up with a bag with the donated material. The day I was there it was winter, there's a guy with a parka, he showed up and said, 'Not my best work,' handed it over and left. That material was put in a blender under a fume hood, and then put on ice and taken to the colonoscopy lab. The colon is seeded with this healthy person's bacteria.

It's the only thing that's been shown to cure chronic infection with the bacteria C. difficile.

A fecal transplant is a very effective and cheap cure. It's not very often that medicine comes up with a cheap, effective treatment. It's sad that it's taken this long to gain acceptance.

Now there are lots of applications for bacterial transplant. Ear bacteria, gum bacteria – there's a lot of difference in how prone you are to gum disease depending on what bacteria are in your gums.

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