It’s common knowledge that the cause of heartburn, indigestion, and GERD is too much stomach acid bubbling up into the esophagus. At least that’s what the commercials for antacids and acid blocking drugs would like us to believe. But is this really the case? When we look at how the digestive system works, the answer is actually just the opposite.
Low Stomach Acid and Heartburn
Heartburn is commonly caused by low stomach acid, or hypochlorhydria. Too little stomach acid, you ask? Yes. In fact, it’s estimated that 90% of heartburn, indigestion, and gas is due to low stomach acid.  To understand how low stomach acid can cause digestive pain, we need to understand how the digestive cascade works, and the role of stomach acid in the cascade.
In simple terms, stomach acid is responsible for the final break down of food in the stomach so that it can be absorbed in the small intestine. The stomach is a very acidic environment in which food is broken down chemically. The pH of the stomach ranges from 1 to 5, depending on where in the digestive process one is. Remember from chemistry, the lower the pH, the higher the acidity. Upon the sight, smell, and taste of food, the hormone gastrin signals cells in the stomach to release acid. The body is anticipating food and produces acid in preparation for break down.
As food enters the stomach at a relatively high pH, gastrin picks up the pace of acid production. In a properly functioning digestive cascade, enough stomach acid is produced to mix with the food and bring the pH to between 1 and 3. At this point, the food (now called chyme) is ready to enter the small intestine by way of the pyloric sphincter. The pyloric sphincter, which connects the stomach and small intestine, is triggered open when chyme reaches the low pH.
In the case of hypochlorhydria, the stomach does not produce enough stomach acid to mix with the chyme for it to reach the required acidity level.
Instead, the chyme is trapped in the stomach and begins to produce pressure and gas. The pressure builds as the chyme expands (think of food sitting in a warm and moist environment). Rather than move down through the pyloric sphincter and continue in the digestive cascade, the chyme is pushed up through the lower esophageal sphincter (LES), which connects the esophagus and stomach, and into the esophagus.
While the chyme is not acidic enough to move to the small intestine, it is much more acidic of a substance than what is intended for the esophagus. The acidic chyme in the esophagus often results in reflux and heartburn, but it is due to low levels of stomach acid, not high.
While low stomach acid is the most common cause of heartburn, it is not the only cause. High stomach acid can be the culprit, though it is thought to be the cause in only 10% of cases.  Another cause is a weakened LES, which results in the sphincter opening inappropriately and allowing stomach acid to enter the esophagus. Pregnancy, hiatal hernia, caffeine, nicotine, alcohol, and some medications are associated with a weakened LES.
Why Low Stomach Acid Matters
Stomach acid plays a critical role in both our digestive and immune systems. Hypochlorhydria’s reach is more than gas, indigestion, and heartburn, and can result in nutritional deficiencies and immune dysfunction.
I’ve written about how nutrition is not just what we eat, it’s also what our body is able to do with the food we eat (click here for that post). The benefits of high quality food are often not realized due to poor digestive function. The nutrients in food can be lost out on if the food is not broken down and absorbed properly; proper stomach acid levels are key for both. For example:
- Poor break down of amino acids. Pepsin is an enzyme that breaks down proteins into amino acids. When pH levels rise above 5, studies have shown that the amount of protein digested drops from 75% to 25% due to reduced pepsin.  Amino acids are the building blocks of neurotransmitters, which communicate information throughout our body and brain. They help regulate important body functions like mood, sleep, and libido, to name a few.
- Malabsorption of vitamins and minerals. Similar to break down, low stomach acid can result in nutritional deficiencies due to a lack of absorbing needed vitamins and minerals, which are critical to thousands of processes in the body. With low stomach acid, iron, calcium, folate, and B12, as examples, can skip absorption and instead be excreted. In the case of B12, stomach acid works to break the bond between the vitamin and the protein it is attached to when it arrives in the stomach. If there is not sufficient stomach acid to break the bond, B12 is not made available for absorption when it moves through the small intestine.
You may have heard that around 70% of your immune system is in your gut. Immune health is usually associated with taking vitamin C and hand washing. But what about gut health and immune health? Not surprisingly, low stomach acid can impact your immunity.
- A reduced first line of immune defense. Stomach acid is our first line of defense against pathogenic microorganisms. Yeast, bacteria, viruses, and parasites are proteins. With proper pH levels, enough pepsin is produced to digest the organisms. Without enough stomach acid, the organisms thrive and cause havoc in the gut.
- Leaky gut. When undigested food makes it way into the small intestine (because eventually the pyloric sphincter will open and allow the chyme to move on, even if it’s not been properly digested), it can tear holes in the intestinal lining. This allows proteins to leave the gut and enter the body, starting an immune response against the foreign invaders. Leaky gut is linked to food sensitivities and allergies, as well as many autoimmune diseases.
So, it turns out low stomach acid is often the cause of heartburn, among other issues. But how does one end up with low stomach acid? And are there ways to naturally increase stomach acid? Look for these answers in an upcoming post! (While I don’t go into food and supplement options for increasing stomach acid, I do talk about lifestyle factors that can improve digestion in this post.)
A Note on Heartburn Medications
The conventional way of treating heartburn, indigestion, and GERD is to use antacids or acid blocking drugs. Antacids work by neutralizing acid. Acid blockers reduce the amount of acid that the stomach produces, and some stop it from producing any at all. Both only address the symptoms of heartburn; they lower the pH of the food that makes its way up the LES, so the burning sensation is not felt in the esophagus. But the spiral of low stomach acid levels continues, if it’s not made worse.
Of course, I am not a doctor. If you are currently taking prescription medication to address acid reflux, you must consult with your prescribing physician regarding your personal decision to discontinue use prior to doing so.