When the Fire Goes Out

Autoimmune Gastritis and the Stomach’s Silent Collapse
How the loss of stomach acid and parietal cells disrupts one of the body’s most elegant feedback systems — and why awareness matters.

By Rex Wiig
Author, Engineer, and Founder of Subsurface Press
Adapted from Thank God for Oxes (forthcoming)

Author’s Note

For most of my life I never gave digestion a thought. Food went in, and chemistry took care of the rest — until the day it didn’t.

When I was diagnosed with pernicious anemia, the end stage of autoimmune gastritis, I began to see digestion not as magic but as engineering — a network of sensors, pumps, and timing loops tuned in perfect feedback. When that design begins to fail, the disturbance ripples far beyond the stomach.

The Stomach — Alchemy of Acid, Enzyme, and Mechanics

By the time food arrives, the stomach is fully awake. The brain has issued its signal, the glands are primed, and the chamber begins its transformation — turning a meal into the elemental fuel of life.

The stomach is a muscular crucible, not a passive sack. About three times each minute it squeezes and folds food through waves of antral peristalsis, kneading it into a uniform slurry called chyme. It’s the biological equivalent of kneading bread dough — each compression mixing nutrients more evenly until acid and enzymes can reach every surface.

Inside, rugal folds unfurl as the chamber fills, guiding flow toward the outlet. They act like internal baffles in an engine, shaping turbulence so that mixing is deliberate, not random.

Beneath these folds, interstitial cells of Cajal serve as pacemakers, controlling the rhythm of contraction. They are the stomach’s metronome — a steady drumbeat keeping muscle, chemistry, and timing in sync.

At the chemical level, the stomach secretes a fluid more potent than battery acid. Hydrochloric acid dissolves food and sterilizes pathogens; pepsin breaks proteins into smaller fragments. The key players are the parietal cells, which create acid and also release intrinsic factor, the carrier protein that allows vitamin B12 absorption in the small intestine.

Through a finely tuned feedback loop, the hormone gastrin regulates these parietal cells. As food dilutes the acid, pH rises; G-cells sense the change and release gastrin, which re-activates the proton pumps to restore acidity — typically below pH 2.0. It’s one of the body’s most precise control systems, adjusting chemistry in real time to match the meal.

When the Fire Goes Out

In autoimmune gastritis, the immune system turns on its own hardware, slowly destroying the parietal cells that maintain this loop. As their numbers decline, acid output and intrinsic factor fall with them.

The stomach keeps calling for acid through surging gastrin signals, but no workers remain to answer. At this point — known clinically as pernicious anemia — acid is gone, B12 absorption collapses, and energy production falters. The conductor keeps waving, but the orchestra pit is empty.

Autoimmunity shows that even a flawless design can fail from self-destruction rather than error.

When Chemistry and Mechanics Falter

Without acid, rhythm weakens. The pyloric sphincter — the muscular valve at the stomach’s exit — no longer receives its chemical cues. Food may linger and ferment or rush through half-digested.

The downstream organs still try to keep pace. The pancreas releases enzymes, and the small intestine absorbs what it can, but efficiency plunges. Proteins remain partly digested; minerals like iron, calcium, and magnesium stay bound; vitamin B12 never arrives.

It’s the same as a factory whose first processing station has failed — the rest of the line still moves, but the product loses quality. Over time, the body runs at half-power: alive, but under-fueled.

Systemic Consequences

As acid wanes, muscle contractions slow and weaken. Food becomes sluggish and under-mixed. When the diluted chyme finally reaches the duodenum (the first part of the small intestine), it lacks the acidity needed to trigger the next relay.

The duodenum releases less secretin and cholecystokinin (CCK) — the hormones that tell the pancreas to send enzymes and the gallbladder to deliver bile. With that signal lost, bile trickles instead of flows; fat digestion stalls. The coordination between stomach, pancreas, liver, and intestine drifts out of phase.

When stomach acid disappears, the digestive orchestra plays out of tune — like a fifth-grade music class trying to find its rhythm. Magnesium needs acid to stay soluble; without it, absorption drops, energy wanes, and muscle tone weakens. Calcium uptake slows, iron remains locked away, and subtle malnutrition accumulates year after year.

Mild low acid (hypochlorhydria) may only dull a few notes — not even noticeable to the untrained ear — but complete loss (achlorhydria) silences the symphony.

The Role of pH and Feedback

Acid doesn’t only digest — it directs. It’s the metronome that keeps timing across the system. When acidity falls, the feedback loop between stomach and duodenum loses calibration. The pylorus may close too soon, trapping food, or open too early, sending chaos downstream.

To the patient, this feels paradoxical: hunger and fullness at the same time, reflux and emptiness alternating without logic. The sensors still exist, but their signals are weak and unreliable.

In chronic atrophic gastritis, even the stomach’s rugal folds flatten and stiffen. Capacity shrinks; mixing power fades. A healthy stomach can stretch to hold nearly two liters, but an atrophic one may manage only half.

When the stomach loses its folds, acid, and rhythm, the burden shifts upward. Every chew matters. Chewing thoroughly isn’t etiquette — it’s compensation. The mouth becomes the new mixing chamber, the tongue and teeth the rugae that no longer exist. So listen to your mother — chew your food!

Passing the Baton

When all systems align, digestion is a masterpiece of timing — feedback loops, valves, and motion running as one. When one link breaks, the entire chain shudders.

Sometimes food lingers too long; sometimes it escapes too early. Either way, what leaves the stomach sets the tone for every system downstream.

Restoring balance begins with understanding. Stomach acid is not an enemy to be suppressed but a spark to be preserved — the ignition that keeps the body’s engine running.

About the Author

Rex Wiig is an author, engineer, and founder of Subsurface Press. After developing autoimmune atrophic gastritis, he applied his background in systems engineering to study how the body’s feedback networks fail — and how awareness can help restore their rhythm.