The glossary.Theglossary.

The most common short-chain fatty acid made in the colon, when microbes ferment fibre. It’s the same molecule that makes vinegar sour (acetic acid).

Channel GG’s name for the stomach, where acid brings the pH down to about 1.5 to 3.5.

An enzyme that unbolts the galactose from raffinose and stachyose, the sugars in beans. Your body doesn’t make it; microbes do.

A building block of protein. About 20 kinds turn up in the proteins you eat; proteases cut proteins back into them.

An enzyme that chips starch into shorter sugars. It’s in saliva and in the juice from your pancreas.

Apple juice fermented twice: yeast turns the sugar into alcohol, then acetic acid bacteria turn the alcohol into acetic acid.

A rod-shaped bacterium that packs itself into a tough spore, rides through stomach acid and germinates in the intestine. Scientists now call it Heyndrickxia coagulans.

A genus of branched, often Y- or V-shaped rods that live mainly in the colon and love fibres like inulin and FOS. “Bifid” means split in two.

A soapy fluid made by the liver and stored in the gallbladder. It breaks fat into tiny droplets so lipase can work. It isn’t an enzyme.

The soft ball of chewed food your tongue shapes and swallows.

A protease from pineapple. It’s why fresh pineapple stops gelatin dessert from setting.

A short-chain fatty acid made when colon microbes ferment fibre. It’s the main fuel for the cells lining the colon.

Colony-forming units: a count of the live microbes in a serving of a probiotic.

The thick soup of food, acid and enzymes that the stomach pushes on into the small intestine.

The most common protein in your body: rope-like strands in skin, tendons and bone. Gelatin is collagen that’s been cooked.

The large intestine: about 1.5 m long, home to most of your gut microbes. It takes back water and hosts the fermentation.

The first milk a mammal makes after giving birth. It carries antibodies such as IgG.

The first stretch of the small intestine, where bile and pancreatic juice pour in. The name comes from Latin for “twelve”: it was measured as about twelve finger-widths long.

The gut’s own nervous system: hundreds of millions of neurons in the gut wall that run digestion, with or without the brain’s input.

A protein shaped to speed up one kind of chemical reaction, such as cutting one kind of bond, without being used up. Enzymes aren’t alive.

The flap that folds over your windpipe when you swallow, so food goes down the right tube.

The single layer of cells lining the gut. It absorbs nutrients, keeps most microbes out and is replaced every few days.

Microbes breaking food down without oxygen, making acids and gas. It’s how you get yogurt, sauerkraut and, Downtown, short-chain fatty acids.

The parts of plant food your own enzymes can’t digest. Some of it feeds the gut microbes; some just adds bulk.

Fructooligosaccharides: short chains of fructose, like a mini inulin. A prebiotic that bifidobacteria love.

A small pear-shaped pouch under the liver that stores bile and squeezes it out when fat arrives.

Hydrogen, carbon dioxide and, in some people, methane, made when microbes ferment fibre in the colon.

What a spore does when conditions get comfortable: it wakes up and grows back into an active cell.

An amino acid. L-glutamine is a main fuel for the cells lining the small intestine.

The pouches along the colon’s wall that give it its puckered look.

Immunoglobulin G, the most common kind of antibody. Colostrum carries plenty of it.

A chain of fructose beads that plants like chicory and Jerusalem artichoke store. Your enzymes can’t cut it; colon microbes ferment it.

A knobbly tuber from a kind of sunflower, rich in inulin. Not an artichoke, not from Jerusalem.

Vegetables, usually cabbage, fermented by lactic acid bacteria such as L. plantarum.

An enzyme on the lining of the small intestine that splits lactose into glucose and galactose.

The acid lactobacilli make. It gives yogurt, sauerkraut and pickles their tang.

A genus of rod-shaped bacteria that make lactic acid. In 2020 it was split into 25 genera, which is why some old names grew longer.

Milk sugar: one glucose joined to one galactose.

An enzyme, mostly from the pancreas, that slices fats into fatty acids and monoglycerides.

A large organ with hundreds of jobs. For digestion, the big one is making bile.

All the microbes living in a place, such as your gut, together with their genes.

Tiny projections on the surface of each cell lining the small intestine. They form the “brush border”, where lactase lives.

The slippery gel coating the gut lining. It protects the lining and keeps most microbes at a distance.

The muscular tube, about 25 cm long, that carries food from your throat to your stomach.

A gland behind the stomach that makes protease, amylase and lipase, plus bicarbonate to neutralise stomach acid.

A protease from papaya, richest in the sap of unripe fruit. The working part of many meat tenderisers.

The stomach’s protease. It’s switched on by acid and works best in it.

Waves of muscle squeezes that push food along the gut. It works upside down and in zero gravity.

A scale of how acidic something is. 7 is neutral, lower is more acidic, and each step is ten times stronger.

A fibre made from glucose, linked every which way, so your enzymes can’t cut most of it.

Food for your gut microbes: something your own enzymes can’t digest that certain helpful microbes eat.

Live microbes you take on purpose, in a counted amount.

A short-chain fatty acid made by colon microbes. Most of it travels to the liver.

Any enzyme that cuts proteins, snipping the links between amino acids.

A bean sugar: galactose, glucose and fructose in a row. Humans can’t split it, so colon microbes ferment it.

Starch that amylase can’t get into, so it reaches the colon like fibre. Cooked-then-cooled potatoes and green bananas have some.

The watery fluid your mouth makes, something like a litre a day. It wets food and carries amylase.

A signalling molecule. Most of the body’s serotonin is made in the gut, where it helps time the squeezes. It doesn’t cross into the brain.

Acetate, propionate and butyrate: small acids colon microbes make when they ferment fibre, roughly three acetates for every one of each of the others.

The long, coiled tube after the stomach, several metres of it, where most digestion and absorption happen. Its inner surface is about 30 m².

A ring of muscle that opens and closes a passage, like the one at the bottom of the oesophagus.

A tough, dry, dormant form some bacteria make to survive heat, drying and acid, then wake from later.

A stretchy muscular bag that churns food with acid and pepsin into chyme. pH about 1.5 to 3.5.

A particular genetic version of a microbe species, named with letters and numbers, like L. acidophilus LA85.

A probiotic and a prebiotic packed together: the crew and their lunch.

The protein seal between neighbouring cells of the gut lining.

A long nerve linking the gut and the brain. Most of its fibres carry messages up from the gut.

Finger-like folds, about a millimetre tall or less, lining the small intestine. With microvilli, they make about 30 m² of surface.

Milk fermented by lactic acid bacteria (traditionally L. bulgaricus and S. thermophilus), which turn lactose into lactic acid.

An enzyme made in its switched-off form. The pancreas ships its proteases this way so they don’t snip the pancreas.