Stomach Acid Provides Immune Protection
True, the process is not 100% effective. Nevertheless, gastric acid does kill most of the bacteria that enter the body with food. Of course, some bacteria survive to take up residence and multiply in the intestinal tract, particularly the large intestine. Bacteria do not thrive in an acidic environment, and it takes an average of 45 minutes for stomach acid to be produced (by healthy, young adults). However, the resting pH of the normal stomach is usually between 5.0 and 6.0, unless proton-pump inhibitors or H2 blockers are being used. Then the pH rises, becomes alkaline, and bacterial microorganisms can flourish, such as helicon pylori bacteria. Actually, it is not the only one, but there will be more about that in the next article.
In this article, let’s discuss stomach acid—hydrochloric acid, to be precise. Those unfamiliar with the digestive process often believe that hydrochloric acid digests salivary and food enzymes (proteins) as soon as they move into the stomach. Even if it did, the enzymes would have 45 minutes to work, much longer for those older than 50. However, hydrochloric acid does not digest food at all! Only enzymes can do that. Rather, hydrochloric acid activates protein-digesting enzymes.
Hydrochloric acid production is under both autonomic and hormonal control. Stimulation to the vagus nerve first affects the enteric nervous system of the stomach wall, and then the oxyntic cells secrete pepsinogen and a smaller amount of stomach acid.
Vagus stimulation also excites the production of the hormone gastrin, which is secreted by the cells in the upper one-third of the stomach and, to a lesser degree, by Brunner’s cells in the duodenum. The stimulation to produce gastrin comes from the stretching of the stomach wall and by the presence of small amounts of either alcohol or caffeine. The hormone is carried by the blood to the oxyntic cells, which greatly increase their secretion of hydrochloric acid and, to a lesser extent, pepsinogen.
In this article, let's discuss stomach acid—hydrochloric acid, to be precise.
The Acidity of the Stomach
The chief cells in the middle portion of the stomach (fundus) secrete the protein-digesting enzyme known as pepsinogen. Pepsinogen is an inactive enzyme that requires hydrochloric acid to be activated and begin protein digestion. So, the major role of hydrochloric acid is to reduce pepsinogen and activate the new molecule, which becomes known as pepsin. Pepsin then splits protein into small peptide fragments.
Those unfamiliar with the digestive process often believe that hydrochloric acid digests enzymes, which are partly protein, when they enter the stomach. However, hydrochloric acid does not digest food—only enzymes can do that. Rather, hydrochloric acid activates the protein-digesting enzyme pepsin.
Pepsin is one of three principal proteases in the human digestive system. The other two—chymotrypsin and trypsin—are produced by the pancreas and become active in the duodenum.
During the process of digestion, these enzymes, each of which is specialized in severing links between various amino acids, collaborate to break down dietary proteins into their components, which can be readily absorbed by the small intestine. The cleavage specificity of pepsin is broad, including amino acids, such as tryptophan, tyrosine, and phenylalanine.
Stomach acid is not made by the cells of the stomach. The ingredients for hydrochloric acid, namely hydrogen (H+) and chloride (C1-), are donated from the blood if it can spare it adequately without disturbing the delicate pH of the blood, which must remain within very narrow limits. Therein lies the key to understanding whether the digestive system is capable of protecting the body and sparing its immune system.
The ingredients H+ and Cl- must pass through the parietal cells and are combined inside the stomach then. This is an important point because stomach acid could easily destroy the wall of the stomach if it were not protected by a thick layer of mucus. Like the salivary glands in the mouth, mucus is secreted by the cells in the stomach to protect it.
Pepsin is one of the primary causes of mucosal damage during gastric reflux. While enzymatically inactive in the alkaline pH (6.8) of the esophagus, pepsin does remain intact (stable) following a gastric reflux event. However, it can then be reactivated upon subsequent acid reflux events. Exposure of the laryngeal mucosa to enzymatically active pepsin (not irreversibly inactivated pepsin or acid) results in reduced expression of protective proteins and erosion of the protective mucosal lining.
When a person needs antacids for their indigestion, it is because the stomach cannot produce a good, quality mucus to protect itself—not because there is too much acid (a physiological impossibility).
In conclusion, stomach acid does protect the body and spare its immune system in a limited capacity. However, the mucosal lining of the entire gastrointestinal tract that houses aggregated lymphatic follicles (white blood cell “hotels,” if you will) attempts to prevent entry of foreign material, such as viruses and bacteria, from entering the body. Inadequate digestion, or reduced hydrochloric acid production, only makes that job more difficult.
This is the third article in this series intended for your family members and patients. I invite your comments and questions by email at [email protected].
Dr. Howard F. Loomis Jr. has an extensive background in food enzyme nutrition. He is the president of the Food Enzyme Institute. The Food Enzyme Institute offers in-person and online seminars to healthcare practitioners around the country. Dr. Loomis published Enzymes: The Key to Health in 1999, The Enzyme Advantage in 2015, and The Enzyme Advantage for Women in 2016. His latest book, What Is Your Nutritional Deficiency?: Find It, Fix It, and Feel Better! was published in 2019. Contact info: 478 Commerce Dr. Suite 201, Madison, Wl 53719, customerservice@ foodenzymeinstitute.com, 800-662-2630.
