Hydrochloric Acid & Protein Digestion

If you experience acid reflux, you may suppress stomach acid with antacids. Yet as long as it stays where it belongs, hydrochloric acid -- a main component of stomach acid -- is extremely important. One of its roles in keeping you healthy is protein digestion. Everything you eat must be broken down by digestive enzymes in order to be absorbed, but protein is the only nutrient that needs to be prepared by hydrochloric acid before your stomach's naturally occurring enzymes can work properly.

Bite of meat on a fork (Image: hillaryfox/iStock/Getty Images)

Protein Structure

Proteins are composed of a long series of molecules called amino acids joined together by peptide bonds. The long strands, or peptide chains, fold up into various configurations, or three-dimensional structures, that hide many of the peptide bonds from digestive enzymes. To absorb protein, your body breaks it down into individual amino acids. The first digestive enzyme that comes into play is pepsin, which is secreted by special cells in the stomach in an inactive form called pepsinogen.

How Hydrochloric Acid Works

Before pepsin can do its job, protein’s three-dimensional structure must be unraveled to expose the peptide bonds to digestive enzymes. This process is called denaturation and happens during cooking and exposure to acid. Hydrochloric acid does not affect peptide bonds. Only enzymes can do that. In addition to denaturing the three-dimensional structure of dietary protein, hydrochloric acid activates pepsinogen and converts it to the enzyme pepsin. Pepsin then begins to break the peptide bonds, forming smaller peptide chains.

What Happens Next

Smaller peptide chains formed with pepsin leave the stomach and enter the small intestine, where they are further broken down by other enzymes secreted by the pancreas. The job of hydrochloric acid is done. It becomes neutralized by bicarbonate, also secreted by the pancreas. The peptide chains are broken down until they can be absorbed as individual amino acids. Protein digestion begins in the stomach with hydrochloric acid and continues in the small intestine without it. The stomach is the only organ where acid belongs.

The Importance of Stomach Acid

Many digestive problems are thought to be the result of too much stomach acid, but that is often not the case. If hydrochloric acid is suppressed, so is protein digestion. This can cause stomach upset, and it also means protein is not absorbed properly. Eventually this can result in protein deficiency. If you are experiencing acid reflux, consult a health care provider to determine whether acid-blocking medication is the best treatment. Hydrochloric acid is also needed for proper absorption of vitamin B-12, which is found in animal protein foods such as meat and dairy. Hydrochloric acid also helps kill microbes that may be in your food.

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