Why does a person with low production of stomach acid have difficulty protein digestion?

Protein digestion primarily occurs in the stomach and small intestine. Hydrochloric acid (HCl) secreted by the stomach plays a crucial role in protein digestion by creating an acidic environment necessary for the activation of pepsin, the primary enzyme responsible for breaking down proteins into smaller peptides.

When a person has low production of stomach acid (hypochlorhydria or achlorhydria), the pH level of the stomach becomes less acidic, impairing pepsin's activity. As a result, proteins are not adequately broken down in the stomach, leading to difficulties in protein digestion.

Here's how low stomach acid affects protein digestion:

Impaired Pepsin Activation: Pepsin requires an acidic environment with an optimal pH of around 1.5-2.0 for its optimal activity. Low stomach acid production leads to a higher pH, inhibiting pepsin's ability to break down proteins.

Reduced Protein Denaturation: The acidic environment in the stomach also helps denature proteins, unfolding their complex structures, making them more accessible to pepsin and other digestive enzymes. Low stomach acid impairs this process, making proteins more challenging to digest.

Impaired Absorption: Undigested or partially digested proteins can reach the small intestine, where further breakdown and absorption occur. However, the presence of undigested proteins in the small intestine can interfere with the absorption of other nutrients, such as vitamin B12, iron, and calcium, which are typically absorbed along with amino acids.

Therefore, low production of stomach acid can lead to incomplete digestion of proteins, resulting in various digestive issues, including protein maldigestion, protein malabsorption, and potential nutritional deficiencies.