Based on a 2,000 calorie diet, it is recommended that 55 to 60 percent of total daily calories be from carbohydrates.

Some of the most common foods contain mostly carbohydrates. Examples are:

• Bread
• Potatoes
• Legumes
• Rice
• Spaghetti
• Fruits
• Vegetables

Many of these foods contain both starch and fiber. The digestible carbohydrates are broken into simpler molecules by enzymes in the saliva, in juice produced by the pancreas, and in the lining of the small intestine.

Starch is digested in two steps: First, an enzyme in the saliva and pancreatic juice breaks the starch into molecules called maltose; then an enzyme in the lining of the small intestine (maltase) splits the maltose into glucose molecules that can be absorbed into the blood. Glucose is carried through the bloodstream to the liver, where it is stored or used to provide energy for the work of the body.

Table sugar is another carbohydrate that must be digested to be useful. An enzyme in the lining of the small intestine digests table sugar into glucose and fructose, each of which can be absorbed from the intestinal cavity into the blood. Milk contains yet another type of sugar, lactose, which is changed into absorbable molecules by an enzyme called lactase, also found in the intestinal lining.

Source – digestive.niddk.nih.gov