Hydrochloric acid in the stomach lowers the pH to the ideal environment for enzymes to digest proteins into units that the body can use. This acidic environment creates an antibacterial environment that protects the body from disease.
The food an individual ingests must be broken into molecules that are able to enter the cell walls. The digestive system uses mechanical breakdown, such as the breakdown that occurs though chewing with the teeth and churning of the stomach. However, the digestive juices are the primary method of breaking food down into usable molecules.
The anticipation of eating, along with smelling and tasting food, causes the stomach to begin secreting hydrochloric acid. By the time the first bite of food enters the stomach, the cells have produced 30 percent of the hydrochloric acid needed to digest the meal. As the stomach fills and is stretched, it produces another 60 percent of the acid. The final 10 percent forms as the material enters and stretches the small intestine.
Patients who take medication to reduce stomach acid production or have low stomach acid for other reasons are at greater risk of digestive tract infections and certain types of food poisoning. The bacteria that normally die in the acidic stomach environment can pass through to the intestines, creating gastric upset.