A change in the pH, or acidity level, can change the shape of an enzyme, preventing it from fulfilling its purpose, according to a Florida State University biochemistry laboratory manual. According to Elmhurst College, enzymes increase the rate of cellular reactions.
One example of an enzyme is lipase. According to Elmhurst College, lipase breaks down lipid triglycerides, or fats. According to Worthington Biochemical Corporation, lipase in the stomach works best when the pH is between 4.0 and 5.0. If the pH falls below 4.0 or rises above 5.0, lipase function decreases and may even stop, preventing the body from breaking down fats in the digestive system. Optimal pH varies for different enzymes.