Gulp: Adventures on the Alimentary Canal

Amylase is a digestive enzyme found in human saliva that breaks down starches into simple sugars that the body can absorb and use for energy. This enzyme is the primary digestive component in stimulated saliva, regardless of a person’s age. Roach explains that readers can actually taste amylase working when they chew bread, as a sweet flavor emerges from the interaction between saliva and starch. The presence of amylase in saliva demonstrates that digestion begins immediately in the mouth, before food even reaches the stomach.

Autocoprophagia is the practice of consuming one’s own feces, a behavior that Roach explores extensively in the context of animal nutrition and digestion. This biological phenomenon occurs naturally in many species, including rodents, rabbits, and other non-ruminant animals, as a way to obtain essential nutrients that are produced by bacteria in the large intestine but not fully absorbed during the first pass through the digestive system. Roach presents autocoprophagia as a normal and necessary nutritional strategy that allows animals to access B and K vitamins, along with other nutrients synthesized in the colon.

Autointoxication was a widespread but scientifically unfounded medical theory popular in the early 1900s that claimed fecal matter remaining in the colon poisoned the body from within. Proponents of this theory believed that waste materials absorbed into the bloodstream caused various health problems ranging from fatigue and headaches to serious diseases. The concept led to aggressive marketing of laxatives, enemas, and colonic irrigation devices as supposed cures for numerous ailments. Medical researchers eventually debunked autointoxication through controlled experiments that demonstrated constipated subjects showed no signs of internal poisoning. Roach uses autointoxication as an example of how commercial interests can promote health myths that contradict the body’s natural evolutionary design.

A bolus refers to the mass of chewed, saliva-moistened food particles that forms in the mouth during the eating process. This formation represents food that has been transformed into what researchers describe as the “swallowable” state through the coordinated action of teeth, tongue, lips, cheeks, and saliva. The creation of a proper bolus requires the entire oral processing system to work together, breaking down food into particles small enough and moist enough to be safely swallowed. In Roach’s exploration of oral processing research, the bolus becomes a central focus for scientists studying dysphagia and swallowing disorders, as the formation of an adequate bolus is essential for safe eating.

Compliant refers to the stretchy, accommodating nature of certain digestive systems that can expand dramatically to hold large quantities of food. In the context of Gulp, Roach uses this biological term to describe stomachs that function as physiological storage units, allowing predators to consume massive meals when prey is available and then digest slowly over extended periods. Animals with compliant stomachs, such as pythons and lions, can accommodate prey many times wider and bulkier than their normal body dimensions. This evolutionary adaptation serves as a feast-or-famine strategy, enabling these predators to maximize food intake during successful hunts and sustain themselves through periods when prey is scarce. The compliant stomach represents a crucial survival mechanism for animals at the top of the food chain, who can afford to remain stationary and vulnerable while digesting without fear of becoming prey themselves.

Fletcherism was an extreme chewing practice promoted by Horace Fletcher in the early 1900s that required individuals to masticate each bite of food hundreds of times until it completely liquefied before swallowing. Fletcher claimed this method would double nutrient absorption while allowing people to consume half their normal food intake, supposedly saving money and improving health. The practice became a widespread fad that attracted followers including famous writers like Henry James and Franz Kafka, as well as government officials who considered implementing it as national policy during World War I. Fletcherism represented one of many dubious nutritional theories of the era that exploited public interest in efficiency and scientific progress while lacking legitimate medical foundation. Modern digestive science has largely debunked Fletcher’s claims, demonstrating that the human digestive system already efficiently extracts nutrients from food without requiring excessive mastication.

The ileocecal valve is an anatomical structure that serves as a one-way portal between the small intestine and the colon, allowing digestive material to flow from the small intestine into the large intestine but preventing backward flow. This valve plays a crucial role in Roach’s discussion of autointoxication because it demonstrates that fecal matter cannot naturally travel backward from the colon into the small intestine, where most nutrient absorption occurs. The valve’s function contradicts the central premise of autointoxication theory, which claimed that waste materials routinely moved backward through the digestive system to poison the body.

Muktuk is a traditional Inuit food consisting of uncooked narwhal skin that serves as an important source of nutrition in Arctic communities. In Gulp, Roach encountered this delicacy during her visit to Igloolik. Despite her initial cultural resistance to eating raw whale skin, Roach discovered that muktuk has a surprisingly pleasant taste. She uses the delicacy as an example of how cultural conditioning shapes food preferences. Additionally, muktuk demonstrates the nutritional wisdom of traditional Arctic diets, as it contains significant amounts of vitamin A and vitamin C, nutrients that are essential in regions where fresh fruits and vegetables are scarce.

An obligate carnivore is an animal that requires meat as its primary food source and cannot survive on a plant-based diet due to biological necessity. In Gulp, Roach uses the cat as the primary example of an obligate carnivore, explaining that cats have evolved to depend entirely on nutrients found in animal tissue. Unlike omnivores such as dogs and humans, obligate carnivores lack the biological mechanisms to process plant matter effectively and obtain essential nutrients from vegetation. The term illustrates how evolutionary adaptation shapes digestive systems, as obligate carnivores have developed specialized organs and metabolic processes designed specifically for processing meat and animal proteins.

Orthonasal olfaction refers to the familiar process of smelling aromas through the external nostrils. This type of olfaction occurs when aromatic molecules enter the nose directly from the environment, such as when someone deliberately sniffs food or when scents naturally drift into the nasal passages during breathing. In Gulp, Roach explains that orthonasal olfaction represents only one component of how humans experience flavor, working alongside retronasal olfaction to create the complete sensory experience of eating and drinking.

A palatant is a flavor coating or additive designed to make food more appealing and appetizing to animals, particularly pets. In the context of Gulp, palatants are the chemical compounds that pet food manufacturers like AFB International apply to dry kibble to entice cats and dogs to eat nutritionally complete but otherwise bland food. These substances work primarily through smell and taste enhancement, often containing ingredients like liver and other organ meats that naturally attract animals. Palatants represent the intersection of animal biology and commercial food production, as they must satisfy both the sensory preferences of pets and the practical needs of human consumers who purchase and serve the food.

Retronasal olfaction describes the internal smelling process that occurs when aromatic gases travel from the mouth through the posterior nares (internal nostrils at the back of the mouth) to reach olfactory receptors in the upper nasal cavity. This process happens when food is chewed or when beverages are held in the mouth, as the warmth releases volatile compounds that then waft upward through internal passages. Roach emphasizes that retronasal olfaction is crucial to flavor perception because it allows people to smell food from the inside while eating, contributing significantly to what most people mistakenly attribute solely to taste buds on the tongue.

The silent period describes a brief moment when jaw muscle activity completely stops during the chewing process. This phenomenon occurs at the precise millisecond when food gives way between the teeth, causing the jaw muscles to reflexively reduce their force to prevent the teeth from colliding with each other. This protective mechanism demonstrates the sophisticated neuromuscular control system that prevents people from damaging their teeth with their own powerful jaw muscles. Roach presents the silent period as evidence of the remarkable sensitivity and precision built into the human chewing apparatus.

Stimulated saliva is the type of saliva that flows from the parotid glands, located between the cheek and ear, when a person eats or anticipates eating. This form of saliva makes up 70-90% of the total saliva that humans produce daily, which is typically between two to three liters. Stimulated saliva appears clear and flows like water, consisting of 99% water along with proteins and minerals. Unlike unstimulated saliva, stimulated saliva has a thin consistency that allows it to mix easily with food and aid in swallowing and digestion.

Unstimulated saliva is the background saliva that flows continuously in the mouth at a much slower rate than stimulated saliva. This type of saliva has a thick, viscous consistency due to mucins, which are long chains of amino acids that create vast webs within the fluid. Unstimulated saliva forms a protective film that clings to tooth surfaces, helping to remineralize enamel and trap bacteria that are then swallowed and destroyed by stomach acids. Despite being more difficult for researchers to work with due to its slimy texture, unstimulated saliva plays a crucial role in maintaining oral health and protecting against infection.