Gastric acid present in the stomach already has a fairly low pH but lowering further through diet can cause discomfort and pain. If you have excess acid, then the goal needs to be to neutralize the excess acid. To neutralize an acid, we need to add a base.
acid + base --> salt + water
Many antacids such as Tums(R) and Rolaid(R) and similar medications are made up of weak bases that will react with the acid and result in neutralization of the excess acid. Acid-base neutralization reactions are used frequently in the lab to determine the concentration of an unknown. Acid-base neutralization reactions are also utilized in the clean-up of chemical spills and/or the processing of hazardous waste.