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Low Stomach Acid
Low stomach acid weakens protein digestion, mineral and B12 absorption, and the first barrier against microbes. We look at age, H. pylori, autoimmunity, stress, zinc, and medications.
What you may be noticing
Heaviness and fullness after protein meals. Burping and bloating soon after eating. Undigested food in the stool. Brittle nails, thinning hair, and fatigue that may reflect low iron, zinc, or B12. Some people even feel reflux, which can seem confusing when acid is low.
Vomiting blood, black stools, difficulty swallowing, or unexplained weight loss need prompt medical evaluation.
Why it is rarely one thing
Stomach acid has three essential jobs. It begins protein digestion by activating pepsin. It releases B12, iron, calcium, and zinc from food so they can be absorbed. And it forms the first chemical barrier against microbes arriving with food. Acid in the upper small intestine also signals the pancreas and gallbladder to release their part of the cascade.
Acid output can fall with age, chronic stress, H. pylori infection, autoimmune gastritis that targets the acid-producing parietal cells, zinc deficiency, and long-term use of acid-suppressing medications. When acid is low, protein digests poorly, minerals and B12 decline, and bacteria may survive into the small intestine, setting the stage for SIBO.
I think of digestion as an information decoding system. Food arrives as complex information, and the stomach begins translating it. When proteins arrive in the gut poorly broken down, the immune system may read them as a threat, a working hypothesis that helps explain why food reactions can follow weak digestion. Autoimmune gastritis and H. pylori-related low acid are well established. Mild hypochlorhydria is harder to measure.
Patterns we look for
- H. pylori infection.
- Autoimmune gastritis: parietal cell and intrinsic factor antibodies.
- B12, ferritin, zinc, and magnesium status.
- Long-term acid-suppressing medication use.
- Stress and sympathetic dominance, since digestion depends on parasympathetic signaling.
- SIBO and microbiome imbalance.
- Thyroid function, including Hashimoto, which travels with autoimmune gastritis.
- Bile flow and pancreatic signaling downstream.
How I evaluate it
The comprehensive functional neurological exam includes autonomic testing and vagal function, because the cephalic phase of digestion begins in the brain at the sight and smell of food.
Functional labs may include B12 with methylmalonic acid, ferritin and iron studies, zinc, a complete blood count, H. pylori testing, parietal cell and intrinsic factor antibodies, gastrin, a thyroid panel, and a comprehensive stool analysis. I coordinate with your gastroenterologist when endoscopy is indicated.
How we address it
In my 8R gut model this is the Replace step: stomach acid integrity, bile flow, pancreatic signaling, and the mineral cofactors that digestive chemistry depends on, such as zinc.
- Identify the cause: infection, autoimmunity, medication, or stress.
- Treat H. pylori when present, with your physician.
- Never stop acid-suppressing medication on your own. Any change is made with your prescriber.
- Support the cephalic phase: slow, seated meals, chewing well, and a calm state before eating.
- Replete B12, iron, and zinc in absorbable forms.
- Use digestive support categories such as bitters, enzymes, and acid support where appropriate, with your care team.
- Then address SIBO, barrier repair, and thyroid or autoimmune balance where present.
Digestion is a cascade that starts at the top. Restore the first step, and the rest can follow.
Book your Comprehensive Functional Medicine Eval/Neurological Exam today to discover what the contributing root causes are that are underlying your health concerns.