In my ongoing effort to remember what I have read, an excellent read from one of my favorite authors, Mary Roach.  She has previously graced the pages of my blog with two books: Stiff and Packing for Mars.

Roach and the Perfected Non-Fiction Format

Roach has perfected the non-fiction story format.  She tackles a subject familiar to all of us and answers the questions we either are too timid to ask or would never have thought of.  Like most good non-fiction writers she provides additional details on the subject and is not afraid to take us down an interesting rabbit hole.  In this book, she does not disappoint as she explores the digestive system from top to bottom.

Meals start with sight, taste and smell. They end up with something you don’t want to see, taste nor smell.

Gulp: Adventures On The Alimentary Canal.

The book is the historical, pathological and physical aspects of the human gut from the mouth through to the other end.  Along the way, Roach pokes at and identifies taboos about the digestive system.  For example why I used the euphemism ‘other end’ rather than ‘anus’ – an enduring human taboo against feces and the need to defecate.

And that is the book in a nutshell, a tour from when food starts (primarily the nose), through where the bolus is prepared and the nutrition is extracted (stomach and intestines) and finally where the finished product is produced (colon, rectum, anus, plop!).  This structure is easily our oldest.  One could argue that the digestive system is the center of the body with other organs and functions there to serve it (brains to find the food, arms to reach it, legs to carry it, etc. with lots of intestinal bugs along for the ride and helping in the process) [p. 321]].

Human Digestive System: Courtesy of http://www.drawitneat.blogspot.com

The Far North: the Nose and Mouth

Roach starts the journey along the alimentary canal at the nose, the most important sensing device for taste.  She proceeds to the mouth where taste continues and the receptors can be fooled.  For example, experiments suggest that cheap wine can be as good as expensive wine  – unless you know which one is which will then bias this opinion p.30.  Or that palatants are used to coat food (human, pet and otherwise) to make otherwise bland or non-tasting food – well taste like something p.42.

A side trip into the eating preferences of our pets is made where we learned that cats are monguesic, meaning they like to stick to one food p. 43.  In contrast dogs will eat almost anything that smells good, wolfing it down in great gulps.  The wolfing part leads to the highest compliment a dog can pay for your cooking, to vomit it up after gulping excessively p.50.

Taste is the doorman to the digestive tract allowing our ancestors to evaluate and eat more of desirable foods or spit out those not meeting muster (and sometimes tasting like mustard)  p.46.  In turn, culture influences to a large extent what we eat and what we accept as substitutions.  Once a child is ten years old, they are relatively fixed in what they eat and it is difficult to change the preferences p.67.  Nevertheless there seems to be a global disinclination to consume organs of the reproductive tract (ovaries, penis, testicles, etc.) no matter the animal p. 72.

As for the claim that the human mouth is a cesspool of bugs, well that is true but the comparison may be off.  Saliva is also good for wound care as it contains various factors which encourage healing  p. 121.  It also contains enzymes which start the digestive process.  For example, the main digestive enzyme in stimulated saliva is amylase.  This enzyme breaks starches down into simple sugars prior to the food heading to the stomach p.110.

Stomach, Intestines and a Mint Wafer

The stomach has two functions, disinfection and storage.  The hydrochloric acid in the stomach kills most bacteria that we would pick up while scavenging on the savanna.  Because food was uncertain there, the stomach was also a handy storage device holding a meal for a few hours.

Don’t eat too much of a meal though as the typical human stomach will rupture with the addition of 3-7 litres of fill (water and otherwise).  Most of the time our stomachs do not rupture due to protective feed back mechanisms including up-chucking that last mint wafer.  For those with failed mechanisms the usual cause for a rupture is the ingestion of sodium bicarbonate after a large meal which can cause the stomach to swell and compress the diaphragm.  As a result, the ‘ruputurees’ were unable to burp or vomit away the building pressure p. 186-188.

Almost there, the Colon and Points South

A bi-product of digestion are the flammable gases such as methane or hydrogen. The gases produced are the result of anaerobic metabolism but they are particularly generated through the digestion of meat, lactose intolerance, legumes or simply the fact that as we get older, we get flabbier inside and out including the colon p. 235.  The existence of gas can lead to dutch ovening your bed partner or to lethal results.

When conducting a colonoscopy usually the gases are removed by protracted bowel-cleansing and the application of carbon dioxide.  Despite these precautions, one sixty-nine year old French man was killed by an exploding pocket of gas (the result of a laxative) while undergoing a colonoscopy.  The spark from the cauterizing loop in the scope ignited a pocket and killed not only the man but also expelled the scope out per Newton’s laws of momentum  p. 225.

In the early 1900’s autointoxication, self-poisoning from your own feces, was considered to be a health risk and lead to a surge in enemas and other methods to clean the bottom pipes.  The younger sister was the 1970’s focus on high fiber diet.  Now science is leaning toward the importance of a bit of transit time (normal duration through the digestive tract is about 30 hours. p.87).  For example, hydrogen sulfide in the bowel may actually thwart some forms of cancers and act as an antiinflammatory p. 262.

The colon primarily focuses on absorbing moisture from the food in transit.  Nevertheless, it is also the place where a number of vitamins and nutrients are created such as B and K.  Because of the poor absorption abilities in the colon, sometimes a return-trip is necessary.  This is the reason that dogs, rabbits and rodents eat their own feces, they are running a meal through the small intestine twice and absorb the nutrients they missed the first time p. 273.

Elvis and Close Encounters of a Fecal Kind

A diseased colon may lack the ability to move material through itself and will begin to swell and stretch.  One such example, a mega-colon of J.W. was 28 inches in diameter at its widest girth p. 289.  Without surgery, the colon that keeps on growing may either push into the other organs or potentially kill its owner through ‘defecation associated sudden death’.  This latter condition, may have killed Elvis.  He suffered from chronic constipation and died pushing in the act of defecation which potentially caused his heart attack.

For some surgery is not needed but a small donation is appreciated.  Fecal transplants moves the flora from a healthy gut to one in need.  Some individuals on potent antibiotics may lose their flora and as a result are at the mercy of whatever bugs happen to come along.  Through a donation and a retrofitted colonscope, a high percentage of patients find relief for a variety of digestive maladies p. ~320.

The People and Things You Will Meet in the Alimentary Canal!

The canal is full of interesting people (err, speaking metaphorically about the book).  A Harley driving sniffer who is effectively a human forensic gas chromatograph.  She can tell you why your wine/beer/olive oil is skunky [p. 24]

Horace Fletcher who promoted thorough chewing of food – to an excess, up to 700 times for a single bite p. ~70.

A convicted murder who ‘hoops’ in contra-band through a stretch rectum.  With practice, good hoopers can smuggle in smart phones, tobacco and even four metal blades, twelve inches long and two inches in diameter p. 203.

Alex St. Martin was a Canadian trapper who was accidentally shot in the side with the wound healing as an open fistulated passage.  Thus it was possible to examine the workings of his stomach in action.  The original surgeon who treated St. Martin and who (un)intentionally created the fistula was William Beaumont. p.89.  The two had a long-standing professional relationship of both master/servant (St. Martin working for Beaumont) and doctor/patient.  Roach discusses in details the suspected intimacy of these two individuals separated by culture and class but joined by a common fistula.  After all, how much better can you know a person after they have stuck their tongue in your fistula?  p. 96

Finally human hair can be found in the digestive tract either inadvertently, through eating or via your steamed rice at the local take out place.  Because hair is 14-percent L-cystein, an amino acid commonly used in meat flavorings, a Chinese food operation was caught using it instead of soy to make cheap soy sauce p. 73.

The After Taste

Although I enjoy Roach’s writing I was left feeling a bit peckish after this read.  I think that she could have explored the physiology in a bit more detail (e.g. some more details how the organs work and interact) and she could have done a deeper dive into common diseases.  For example, I was hoping to read more on irritable bowel syndrome, gluten intolerance, burst appendices or diverticulosis.  Nevertheless, I left the book satisfied, not stomach bursting but satisfied