w/CS: Gulp: Adventures on the Alimentary Canal, Mary Roach

January-February 2024

Gulp: Adventures on the Alimentary Canal, Mary Roach, 2022. I am reading the with CS. Mary Roach is a popular science writer who has developed a ‘brand’ of doing popular science books with toungue-in-cheek titles like Gulp, Stiff, Bonk, and so forth.

My impression after the first two chapters is that it will be a fun, fairly light read. She is very good at tossing in the amusing descriptive phrase.

Contents

Introduction

Roach is good with adding amusement via offbeat similes:

“A pill cam documents its travels like a teen with a cell phone, grabbing snapshots second by second...” (p. 16)
“Inside the stomach the images are murky green with bits of drifting sediment. It’s like footage from a Titanic documentary.” (p. 16)

And her offbeat descriptions don’t necessarily just add humor – the often offer insight or useful perspective shifts:

“I found it both appalling and compelling, all the moreso because I knew a parallel world existed within my own pinkish hull.” (p. 17)
“…curiosity began to push aside disgust or fear or whatever it was that so reliably deflects mind from body.” (p. 17)

C1: Nose Job: Tasting has little to do with taste

We begin with an introduction to Sue Langstaff, a sensory analyst who works with the wine and olive oil industries in central California. In a series of anecdotes we learn about what her job entails, and that taste is mostly smell, and that the expertise of an analyst like her is in identifying and describing components of complex odors. “Her words come out faster, lit by interest and focus.“
In wine there is not much of a correlation between quality and price; nor does complexity equate with quality.
Roach attends an olive oil tasters tryout run by Sue Langstaff. “All around me, the people make sounds like ill-mannered soup eaters, aerating the oils to free the aromatic gases.“
Sensory analysis is a matter of practice. People may be very adept at analyzing the flavors of, say, olive oil, but not do well at analyzing other flavors/odors.
Different foods have their own sensory lexicons: there are lexicons for wine, olive oil, chicken nuggets, mutton, ripening anchovies, strawberry yogurt, almonds, rice, pond-raised catfish, cat food, and much more.

C2: I’ll have the Putricine: Your pet is not like you

We begin at AFB, a company that makes flavor coatings — palatants — for pet kibble. The goal is to balance the very different preferences of pets and their owners.
WWII lead to the development and popularity of dry pet foods, because a tin shortage led to a shortage of metal for canning, including canning for pet food. And, as it turns out, consumers, at least humans, appreciated the dry, non-smelling, less-messy attributes of kibble.
Cats are monoguesic — they stick to one food. Even outdoor cats tend to be birders or mousers.
Palatants. Pyrophosphates are like crack for cats. There are at least three different kinds…
Writing note: On page 44, the cap is unscrewed and the pyrophosphate is poured into a cup. But then the author spends two pages talking taste and how its studied. Finally, she writes: “Enough stalling. Time to try the palatant. …It has no smell. … It tastes like water spiked with strange.” –So this is a nice job of creating tension, and I think it avoids leaving the reader feel let down at the end.
We now talk about how rodents experience taste — we see mice licking their whiskers of a good tasting substance, and trying desperately got get a bad tasting substance off of their tongues. Then there is discussion of other organisms that have some sort of sense of taste…
By adding strawberry or vanilla, scents that consumers associate with sweetness, it is possible to fool consumers into thinking something tastes sweeter than it is.
Something that is just starting to decay still has its full nutritional value…
Dog food is more nutritionally valuable than much of what humans eat; this is due, in part, to the fact that it is made up of organ meets, which have a lot more vitamins and other positive nutritional attributes that the ‘muscle meats’ that we favor, at least in the US.

Nice image: “I see an undifferentiated ground-cover of bobbing cat heads, but nod anyway.” (p. 300 )

C3: Liver and Opinions: Why we eat what we eat and despise the rest

Among the Inuit. Inuit traditionally eat organ meats, raw and cooked, and it turns out they are extremely nutritious (much more so than muscle meat).
In the US in WWII there was a project to convince people to eat organ meats. Margaret Mead was called upon to study ways of getting people to change their eating habits. Kurt Lewin gave lectures to home makers promoting organ meats.Neither of these appears very successful. A better approach was to simply get people to try things, preferably multiple times: “People like what they eat, rather than eat what they like.” (Kurt Lewin) The most effective way to change dietary preferences is to get leaders and celebrities to sat something, and other people will imitate them.
Western explorers have starved to death rather than eating what the natives eat.

C4: The Longest Meal: Can Thorough Chewing Lower the National Debt

Horace Fletcher created and promoted “Fletcherism,” which was the doctrine of chewing food extremely well, until it essentially dissolved in the mouth. He argued this approach released all the nutrients in a food, and that as a consequence people needed much less food. This was a very attractive proposition during the food shortages that attended WWII.
The Model Gut is a computerized table-top digestive track simulator.
While saliva carries an enzyme that starts to break down food, the same enzyme is manufactured by the pancreas.
Alexis St. Martin. A fur trapper who was shot in the abdomen, and the resulting wound didn’t heal entirely and provided access to the interior of his stomach. His surgeon, William Beaumont, recognized this as an opportunity and conducted over a hundred experiments, resulting in a book.
An unvalidated ChatGPT summary of William Beaumont’s findings:

Digestive Process: He observed how food was physically broken down in the stomach and noted the importance of the stomach’s movements in this process.

Gastric Juice: Beaumont collected gastric juice from St. Martin’s stomach, studying its chemical properties and role in digestion. He identified that gastric juice contains hydrochloric acid and enzymes that are crucial for the digestion of food.

Digestion Time: He conducted experiments to determine how long various foods took to digest, noting that different foods had significantly different digestion times.

Temperature and Digestion: Beaumont found that the temperature of the stomach influences digestion, with warmer temperatures generally enhancing the process.

Emotions and Digestion: He also observed that St. Martin’s emotional state could affect his digestive process, with agitation or illness slowing down digestion.

—ChatGPT

…reading break…

C5: Hard to Stomach: The acid relationship of William Beaumont and Alexis St. Martin

Beaumont — who did surgery on St. Martin that resulted in a fistula in his stomach — employed St. Martin as an experimental subject (and house servant) for decades. He did a variety of experiments that either involved introducing materials directly into St Martin’s stomach, or extracting his digestive fluids and using those in experiments.
The author raises questions about whether Beaumont deliberately created the fistula in St. Martin’s subjects, about whether St. Martin was exploited by Beaumont, and also about the nature of the relationship between them, which evidently became rather fraught in later years.
In the 19th century, and before, it appears that it was not uncommon for physicians to smell and taste various bodily fluids of their patients, including stomach acid, mucus and pus.
Beaumont overstated the role of gastric acid. In fact, humans can get by with very little gastric acid — its primary function is to kill bacteria; what is more important in digestion is pepsin and pancreatic enzymes produced in the small intestine.
The main contribution of Beaumont’s research was to show that digestion was a chemical process rather than mechanical; but European researchers had already show that this was the case in animals.

C6: Spit Gets a Polish: Someone ought to bottle the stuff

Humans secrete 2-3 pints of saliva every day. Both the composition and the amount of saliva produced varies significantly among humans.
There are two types of saliva: stimulated and unstimulated. The first is produced in response to stimuli associated with eating; the second is produced constantly to keep the mouth and teeth moist. The two types of saliva are quite different.

Stimulated Saliva

Stimulated saliva constitutes 70-90% of the saliva we secrete, is produced by the parotid glands between the cheek and the ear. It looks, tastes, and flows like water.
- It is produced in response to chewing, but not in response olfactory or gustatory stimulation. It functions to dilute acidic food to buffer the pH of the mouth in a range to prevent it from damaging tooth enamel, and to aid in swallowing the bolus.
  - The main enzyme in stimulated saliva is amylase, which breaks down starch into sugars.
  - (Babies saliva has lipase, which aids in the digestion of milk; adults primarily secret lipase in their intestines.)

Unstimulated Saliva

Unstimulated saliva is viscous, sticky and elastic — this is due to the fact that it contains muffins, long chains of repeating amino acids. Unstimulated saliva protects the teeth; it contains proteins the bind to the calcium and phosphate in the teeth, and serve to remineralize them. Unstimulated saliva also traps bacteria and carries them to the stomach, where they are destroyed by the stomach acid.
Unstimulated saliva also has antimicrobial properties, and contains an anti-clumping agent the prevents bacteria from clustering together in colonies on the teeth or gums
I’m still a little unclear on this: does unstimulated saliva kill bacteria, or does it carry them to the stomach where they are destroyed. If it is so antimicrobial, why are there so many bacteria that grow only in the mouth?
Human saliva contains histatins, which speed the closure of wounds; similarly, animal wounds that are licked heal faster than those that are not.
Human saliva also contains anti-viral agents; colds are not spread by drinking from a contagious person’s glass, but rather by touching it and then bringing fingers to the nose or eyes.

Saliva contains several key antimicrobial agents:

Lysozyme: An enzyme that attacks the cell walls of bacteria, causing them to lyse or break apart.

Lactoferrin: Binds iron, making it unavailable for use by bacteria, thus inhibiting their growth.

Peroxidase systems: Catalyze reactions that produce antimicrobial compounds, such as hypothiocyanite, which can inhibit bacterial growth.

Defensins and other peptides: Small peptides with broad-spectrum antimicrobial activity against bacteria, fungi, and viruses.

Immunoglobulins: Saliva contains IgA (predominantly), IgG, and IgM, which play roles in neutralizing pathogens and preventing colonization.

– ChatGPT (output validated by web searches on each component on 18 Feb 2024)

The human salivary peroxidase system (SPS) contributes in several ways to the maintenance of good oral health. The SPS is one of the non-immunoglobulin defense factors which regulate the quantity and species distribution of oral micro-organisms. The SPS also prevents toxic accumulations of hydrogen peroxide (H2O2) and it inactivates many carcinogenic and mutagenic compounds. The salivary glands secrete a peroxidase enzyme (salivary peroxidase) as well as the thiocyanate ion (SCN-, derived from diet). The enzyme catalyzes the oxidation of SCN- by hydrogen peroxide (H2O2). The H2O2 is excreted by oral bacteria and by host cells in amounts which vary with the state of cellular metabolism, the diet and other factors. Oxidized forms of SCN- temporarily inhibit the growth, respiration and metabolism of most species of oral bacteria. The major oxidized form generated in the mouth is the hypothiocyanite ion (OSCN-) which must reach a minimum threshold concentration before bacterial inhibition occurs. This threshold concentration varies from species to species. The concentration of OSCN- in the mouth rises and falls with the availability of H2O2. This natural rise and fall, together with bacterial variation in sensitivity to OSCN- inhibition, suggests a role for the SPS in the regulation of the oral microflora. As a result of the rapid consumption of H2O2 by the SPS, host cells are protected from a toxic build up of this potent oxidizing agent. The major product of the reaction, OSCN-, does not harm human cells. Many carcinogenic and mutagenic compounds may serve as substrates for the SPS and be oxidized to less harmful compounds.
– J Oral Pathol. 1984 Dec;13(6):573-84. doi: 10.1111/j.1600-0714.1984.tb01459.x.

Query to ChatGPT If saliva is so antimicrobial, is applying it to wounds a good idea?

Regarding the application of saliva on wounds, the traditional practice of “licking wounds” may have some basis in the antimicrobial properties of saliva. However, this practice is not recommended by modern medical standards for several reasons:

Risk of Infection: While saliva has antimicrobial properties, it also contains a wide variety of bacteria and viruses that are part of the normal oral microbiota. Introducing these microorganisms into an open wound can increase the risk of infection rather than prevent it.

Insufficient Antimicrobial Activity: Although saliva contains antimicrobial agents, their concentration and efficacy may not be sufficient to prevent infection in an open wound, especially against more resistant strains of bacteria or in contaminated environments.

[ChatGPT also notes that modern antiseptics, antibiotics, etc., offer preferable treatments.]
— ChatGPT [unvalidated output]

C7: A Bolus of Cherries: Life at the Oral Processing Lab

Chewing varies in speed and quantity and quality among people: it is a physiolgical fingerprint.
Human teeth can detect a grain of sand or grit 10 microns in diameter (human hair is 50-100 microns)
Crisp and crunch appeal to us because they signify freshness. Snack foods are designed to simulate this. “People like it most when it is around 90 to 100 decibels ,,, to achieve that you need about 100 bubbles bursting in rapid succession.”

C8: Big Gulp: How to survive being swallowed alive

A healthy adult generates a new stomach lining every three days. This is that answer to why the stomach lining isn’t digested by gastric juices: it is, but it is replaced as fast as it is consumed.
Also, key components of gastric juices are secreted separately so that they don’t damage the cells that produce them.
Penguins can shut down their digestion by lowering the temperatures of their stomach; this allows them to carry food back to their nests — which may be 2- to 3-days away — without digesting it.

…reading break…

C9: Dinners Revenge: Can the Eaten Eat Back?

A very light chapter. Not very interesting. Two points:

With the exceptions of parasites, ingested organisms cannot eat their way out of another organism’s stomach..
Cows, and other ruminants, have very large stomachs, because what they are ingesting has little nutritional value so they must consume a lot of it and they must spend a lot of time digesting it.

C10: Stuffed: The Science of Eating Yourself to Death

Another not very interesting chapter. It is about overeating, and whether the stomach can burst. The answer is that, for the most part, protective mechanisms triggered by stretch sensors in the stomach lining will kick in before it bursts. However, various things ranging from opium to physical block at to willpower can subvert that.

C11: Up Theirs: The Alimentary Canal as a Criminal Accomplice

This is better than the last two, but still there the signal to noise ratio is pretty low. The dominant theme of the chapter is smuggling contraband in the rectum; there is a little bit of interesting physiology behind how this works.

Six to eight times a day a peristaltic contraction squeezes the contents of the colon along; this can be triggered by eating via something called the gastrocolic reflex.
When a load presses against the rectal walls with sufficient pressure, stretch receptors trigger the defecation reflex which involves the rectal walls squeezing and the anus relaxing.
According to one man who smuggles things in his rectum, although one must initially combat the urge to defecate, after several rounds of suppressing it, it will subside. This is confirmed by the experience of medical doctors.
People can suppress defecation for a long time — on the order of days — and one smuggler is reported to have suppressed it for twenty four days. Once the rectum becomes distended, this will trigger a slowing or cesssation of activity in the intestines and even the stomach.
Anal tissue is among the most densely inervated in the body. It must be able to distinguish between solid, liquid and gas, and selectively release all or a part of it.

…reading break…

Inflamable You: Fun with Hydrogen and Methane

About 80% of flatus is hydrogen.
About 30% of people also produce methane in their guts.
The flammability of hydrogen and methane is one reason for the thoroughness of colonoscopy preparation; there is at least one incident of a fatality due to ignition of flatus during the cauterization of polyps during a colonoscopy.
Ruminants do not belch, but rather can reroute flatus to their lungs. The theory is that the prevents noises that might alert predators.

Dead Man’s Bloat: …Flatulence Research

Difficulties digesting oligosaccharides (e.g. in beans) and lactose (e.g., milk) can lead to flatulence; in both cases taking appropriate enzymes can eliminate or minimize these effects.

Smelling a Rat: …noxious flatus…

Three chemicals are largely responsible for the smell of flatus: hydrogen sulfide, (rotten eggs) is the major contributor to odor, even though it is only 1-3 ppm of flatus; two other odor-producing components are methanethiol (decaying vegetables), and dimethyl sulfide (sweet).
Hydrogen sulfide appears to prevent inflammation in the gut, and reduces ulcerative colitis and cancer; aspirin and other NSAIDs cause inflammation in the gut.
Activated charcoal pills are ineffective for dealing with intestinal gas; binding sites appear to be all used up by the time the charcoal makes it to the gut.
Daily doses of peptobismal work, but can irritate the gut.
Devrom, which is bismuth subgallate, reduce 100% of sulfur gas odor.
The ileocecal valve prevents backflow from the colon into the small intestine.

…reading break…

Eat Backwards: Is the Digestive Tract a Two-way Street?

Talks about the history of attempting to provide nourishment through the rectum. The takeaway: It doesn’t work.

I’m All Stopped Up: …constipation

Discusses Hirschsprung’s Disease, in which the nerves that line the colon are not completely laid down, and their is an area where peristalsis ceases to work, and digests builds up, leading to constipation and a huge enlargement of the colon. Elvis Presley apparently suffered from this. Besides the discomfort and debilitation, it can lead to death in two ways: one is the effort to move one’s bowels can lead to heart flutter and eventual cardiac problems, and the other is that relaxation following an intense effort can lead to pulmonary embolism caused by a surge of blood afterwards.

The Bristol Stool chart ranges from 7 (liquid), through solid (4 and 3) to constipated lumps (1).

The Ick Factor: …

Discusses the microbiome, with a focus on fecal transplants as a means of addressing C-difficile, Chron’s disease, and other forms of diarrhea. Fecal transplants seem to be extraordinarily effect (80-90% cure rates), but have been very slow to be approved as a certified form of treatment.
For every human cell in your body, there are nine (much smaller) bacterial cells.
Some very beneficial compounds, such as polyphenols, are not absorbed in the intestine and rely on colonic bacteria for their breakdown. Likewise, charred red meat is not carcinogenic until is is metabolized by colonic bacteria. And, more generally, the type of colonic bacteria you have may determine the effectiveness of drugs you are taking.
The bacterial species in your colon are much the same as what you had at 6 months, about 80% of which were passed on from your mother.
The digestive tract has its own immune system and its own ‘brain’ — the enteric nervous system.
Probiotics are mostly just a marketing gimmick: colonic bacteria are aerobic, but probiotics on the market are, with one exception, aerobic.

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