Role of Stomach Acid in Digestion

Written by Lindsay Boyers; Updated December 02, 2018

Digestion is a complicated process that involves a lot of structures, digestive juices and enzymes all the way from your mouth to, well, the other end of your body. One of the most important substances involved in digestion is hydrochloric acid (HCl for short) or, in other words, your stomach acid. Without it, digestion and absorption of certain nutrients wouldn't even be possible. Stomach acid allows you to digest protein, helps prevent you from developing infections and food poisoning, makes sure you're absorbing vitamin B12 properly and signals the other digestive organs to release their juices and enzymes and muscular contractions that make digestion smooth and easy.

Protein Digestion

Stomach acid doesn’t digest protein directly, but it activates an enzyme called pepsin, which breaks proteins down into amino acids that your body can absorb. When you eat protein, the chief cells in your stomach wall release a substance called pepsinogen. When pepsinogen mixes with stomach acid, it activates to become pepsin. Before stomach acid is released into the stomach, the stomach has a pH between 5.0 and 6.0. When the stomach acid enters the stomach, it drops the pH to a range of 3.0 to 5.0. Pepsin only activates in this acidic pH range, so if there isn’t enough stomach acid, the activation of pepsin, and the resulting protein digestion, would be impossible.

Infection Prevention

The food and drinks you consume naturally contain microbes, or bacteria and fungi. There’s really no way around that; but these bacteria and fungi cannot survive in an acidic environment. Because of this, stomach acid plays a critical role in preventing these pathogens from causing an infection. For example, research shows that E. coli is inactivated when stomach acid creates a pH of 1.5 to 4.0 in the stomach. On the other hand, if your body is low in stomach acid, it makes you more likely to develop infection and foodborne illness.

Vitamin B12 Absorption

The most significant dietary sources of vitamin B12 are animal products, which are also rich in protein. In order to get access to the vitamin B12 attached to these proteins, you need stomach acid to activate pepsin, which breaks down the protein and releases the vitamin B12. Without adequate amounts of stomach acid, vitamin B12 stays bound to proteins and never becomes free to bind with other substances that carry it through the intestinal wall into your blood.

Chemical Signaling

The release of stomach acid into the stomach also produces chemical signals that trigger other parts of digestion and other digestive organs. The presence of stomach acid and the drop in pH that follows signal the pancreas to produce and release its digestive juices and enzymes, which include bicarbonate, protease, lipase and amylase. Bicarbonate helps neutralize stomach acid, while protease, lipase and amylase help break down proteins, fats and carbohydrates, respectively. The presence of stomach acid also triggers peristalsis, or the muscle contractions of the intestines that help crush and physically move the food and digested particles through the rest of the digestive tract.

About the Author

Lindsay Boyers

Lindsay Boyers is a holistic nutritionist with a Bachelor's degree in food and nutrition and a certificate in holistic nutrition consulting. She has a background in functional nutrition and 10 published books, including The Everything Guide to Gut Health, The Everything Guide to the Ketogenic Diet, and The Everything Guide to Intermittent Fasting.

bibliography-icon icon for annotation tool Cite this Article