You Might Have Too Little Stomach Acid
If you reach for antacids when your digestion feels off, you're not alone. The assumption most of us carry is that digestive discomfort means too much acid. But in clinic, the picture I see far more often is the opposite. Low stomach acid is often behind so many of the gut complaints my clients come to me with: bloating, heaviness after meals, undigested food in stools, reflux, poor iron levels, and low B12. And once you understand what stomach acid actually does, it becomes hard to overstate how central it is to everything else.
Your Digestion Starts Before You Even Pick Up a Fork
Here's something that surprises most people: digestion begins in the brain, not the stomach. The moment you smell food, think about what you're going to eat, or sit down to a meal, your vagus nerve fires and kicks off what's called the cephalic phase of digestion. This accounts for roughly 20–30% of the stomach acid you produce for that meal.
This is why eating at your desk, scrolling your phone while you eat, or grabbing something on the run really matters. If your nervous system is in a stress response, that first crucial wave of stomach acid production simply doesn't happen properly. In TCM, we talk about the Spleen and Stomach needing calm, warm conditions to do their work. The cephalic phase is essentially that principle written in physiology.
Once food actually lands in the stomach, a second phase kicks in - gastric distension and the presence of proteins both stimulate further acid production, accounting for around 60–70% of the total output from a meal. The stomach is supposed to be a highly acidic environment, sitting at a pH of roughly 1.5–3. That's about a million times more acidic than your blood.
What Stomach Acid Is Actually Doing
Stomach acid (hydrochloric acid, or HCl) is produced by specialised cells in the stomach lining called parietal cells. These same cells also produce something called intrinsic factor, which is the only carrier protein your body has for absorbing B12. Without adequate HCl production, you can eat all the B12-rich food you like and still come up deficient.
Beyond B12, HCl is doing the following essential work with every meal:
Denaturing proteins so digestive enzymes can break them down properly
Activating pepsinogen into pepsin (your main protein-digesting enzyme)
Triggering the release of secretin, which prompts the pancreas to release its digestive enzymes
Stimulating the gallbladder to contract and release bile, essential for fat digestion
Sterilising the small intestine, which helps prevent bacterial overgrowth (SIBO)
Facilitating the absorption of iron, calcium, magnesium, and zinc
Maintaining the right pH gradient throughout the digestive tract for a healthy, diverse microbiome
When HCl is low, this whole cascade starts to fall apart. Proteins aren't properly broken down. The gallbladder doesn't get its signal to contract. Nutrients slip through unabsorbed. Bacteria that should be killed off survive to set up camp further down the gut.
Why So Many of Us Are Running Low
A few key drivers come up again and again in clinic:
Stress is probably the most common. When your nervous system is in a sympathetic state, the physiological equivalent of running from a threat, blood flow is redirected away from the digestive system. The proton pump that creates stomach acid requires ATP (cellular energy) to function. If that energy is being diverted to deal with chronic stress, a demanding job, a difficult relationship, or even an ongoing infection, digestive function gets deprioritised. There is a real and well-documented link between chronic fatigue and poor digestion for exactly this reason.
H. pylori is a bacterial infection that colonises the stomach lining and directly suppresses parietal cell function, driving HCl production down. It's more common than most people realise, and it can sit quietly for years before symptoms surface, which can include a gnawing or burning feeling in the stomach between meals or at night, hiccups, dark tarry stools, nausea, and persistent bloating. It can be tested via a breath test or stool test; your GP can arrange the breath test. If H. pylori is suspected, it's worth addressing before doing anything else to support stomach acid.
PPIs and antihistamines are two medication classes worth understanding. PPIs (proton pump inhibitors) work by binding to the very pump that makes stomach acid, and once bound, that pump is inactivated permanently. New pumps are synthesised to replace them, which is why it takes several days for PPIs to reach full effect, and why coming off them abruptly causes a significant rebound surge in acid. If you're working towards reducing or stopping PPIs, a structured, supported taper is essential; a sudden stop is likely to make things feel considerably worse before they improve. First-generation antihistamines (the older kind, like original Benadryl) work by blocking acetylcholine, which also directly stimulates acid production, they're why these drugs cause dryness, constipation, and digestive sluggishness as side effects.
Age is a contributor. Stomach acid production declines naturally over time, with research suggesting roughly a 30% reduction by the age of 55.
Zinc deficiency matters here too. The enzyme that produces HCl - carbonic anhydrase, requires zinc as a cofactor. Low zinc impairs acid production and also the bicarbonate production that protects the duodenum. This is why zinc is frequently included in gut support protocols.
Signs Your Stomach Acid Might Be Low
Rather than self-diagnosing, I'd encourage you to look at the full picture. The following symptoms, especially in combination, are worth taking seriously:
Burping frequently during or after meals
Gas and bloating within an hour of eating
Feeling of fullness or heaviness after meals that sits for a long time
Difficulty digesting high-protein meals, meat or eggs that feel like they're "sitting" in your stomach
Offensive breath
Hard, slow bowel movements
Finding it difficult to digest raw fruit and vegetables
Visible undigested food in stools
Where to Start
The apple cider vinegar test is a first step. Dilute two tablespoons in a small glass of water and drink it with a meal. If you feel a burning sensation, the priority is to heal the gastric mucosa first, your gut lining needs some support before you add any acidity. DGL (deglycyrrhizinated liquorice root), slippery elm, marshmallow root, and aloe vera inner leaf gel are all useful here, and a practitioner-led protocol typically runs for six to eight weeks.
If there's no burning sensation, a single HCl capsule (600–750mg) with your largest meal is a common starting point. The goal is to support, not replace, what your body should be making. Rebuilding parasympathetic tone through diaphragmatic breathing, mindful eating, and slowing down at mealtimes is just as important as any supplement.
This is work I support my clients with through nutritional consultations. If you're dealing with persistent gut symptoms, booking a full assessment is always the best place to start, symptoms rarely exist in isolation, and understanding the whole picture makes the difference.