Carbohydrates, which include sugars and starches, are the body's primary source of energy and, along with fats and proteins, one of the three major nutrients in the human diet. Carbohydrate intolerance is the inability of the body to completely process the nutrient carbohydrate into a source of energy for the body, usually because of the deficiency of an enzyme needed for digestion.

Digestion of food begins in the mouth, moves on to the stomach, and then into the small intestine. Along the way, specific enzymes are needed to process different types of sugars. When these enzymes are inadequate, the result is carbohydrate intolerance.

Carbohydrate intolerance can be primary or secondary. Primary deficiency is caused by an enzyme defect present at birth or developed over time. The most common is lactose intolerance. Secondary deficiencies are caused by a disease or disorder of the intestinal tract, and disappear...