Whether breaking down foods or healing from injury, nearly every process the human body performs involves chemical reactions. Enzymes are proteins that act as the catalysts for these chemical reactions. Every cell in the body uses enzymes for building, maintenance, and repair. The human body produces many enzymes on its own, however natural production of enzymes begins to decline as early as age 25. Joint pain, circulatory problems, slower healing, and an increase in the incidence of disease are all too common with people who are enzyme deficient and suffering the effects of aging. Types of Enzymes Enzymes fall into three main categories: food enzymes, digestive enzymes, and systemic enzymes. Food enzymes.