Science journalist Mary Roach has chosen the alimentary tract as the subject of her latest book. She takes us on a tour through the digestive tube from the entrance to the back passage with flexible scope for illuminating the journey with extraordinary facts and figures on the way. The tales of eccentric scientists and their studies along with the footnotes are worth the price of admission to the exploration alone. Taste and smell are the doormen for the digestive tract, chemical scanners for possible dangerous elements (bitter, sour) and desirable (salty and sweet). Saliva is more than a lubricant. It contains enzymes that start breaking down food that are also used in laundry detergents. How we chew is a physiological fingerprint and we learn of Fletcherism, chewing each bite at least 70 times to release nutrients, still used today by some as a slimming aid. Chew and spit as a weight loss strategy is mentioned. Elton John was falsely accused of practising this by a tabloid and received healthy damages. Chewing without swallowing is counterproductive. Everything above the neck (smelling, tasting, seeing) drives eating and everything below puts the breaks on. Why do we enjoy crispy, crunchy foods that the food industry has exploited? Why do Inuits prefer Caribou liver, brain, eyes and stomach contents to eat rather than steak, or babies preferring brain and bone marrow over sweet foods when presented with a selection of mashed foods? The likely answers are here.
Air swallowing (aerophagia) or overeating producing burps , belching and heartburn are explained, as are stomach rupture and competitive eating with startling revelations. The small bowel is not given much detail (it absorbs digested food) although stories of 'tummy' rumbles due to gas (borborygmi) led patients to believe they had snakes, frogs or newts inside them sometimes resulting in needless surgery, in the 1800's. The large bowel (colon) and beyond are more interesting to the author. Smuggling drugs, mobile phones, razor blades, but not explosives, either by swallowing or rectal insertion (hooping) are covered. Flatus and it's many properties are discussed in detail with anecdotes of the dangers of its flammability. Megacolons (both grossly increased in length and diameter) are linked to constipation and death. Elvis Presley is subjected to lengthy speculation concerning the role of his large bowel in the cause of his demise. The colon is a drying machine with the products stored in the rectum before passage to the sensitive anus ('it has to know what's knocking on it's back door') before defaecation. The use of per anum (via the anus) is amusingly confused with per annum (yearly). Hence the Sri Lankan importer who needed 3,600 metric tons of garlic per anum and someone who questioned how many people died from horse riding per anum?
Mary Roach has given a humorous well-researched account of the subject in her inimitable style. As a doctor I am familiar with the digestive tract and particularly enjoyed the history, bizarre facts and presentation from a completely different perspective. Recommended as a funny and educational read without laying the science on too thickly.