Resistant starch (RS) is starch and starch degradation products that escape digestion in the small intestine of healthy individuals. Resistant starch is considered the third type of dietary fiber, as it can deliver some of the benefits of insoluble fiber and some of the benefits of soluble fiber.
Some carbohydrates, such as sugars and most starch, are rapidly digested and absorbed as glucose into the body through the small intestine and subsequently used for short-term energy needs or stored. Resistant starch, on the other hand, resists digestion and passes through to the large intestine where it acts like dietary fiber.
Resistant starch has been categorized into four types:
RS1 Physically inaccessible or digestible resistant starch, such as that found in seeds or legumes and unprocessed whole grains
RS2 Resistant starch that occurs in its natural granular form, such as uncooked potato, green banana flour and high amylose corn
RS3 Resistant starch that is formed when starch-containing foods are cooked and cooled such as in legumes, bread, cornflakes and cooked-and-chilled potatoes, pasta salad or sushi rice. The process of cooking out the starch and cooling it is called retrogradation.
RS4 Starches that have been chemically modified to resist digestion. This type of resistant starches can have a wide variety of structures and are not found in nature.
There is some discussion about resistant dextrins being described as "resistant starch". Resistant dextrins are not starches, and they can be soluble or insoluble. They might be described as "starch degradation products", which is literally included in the EURESTA definition, but their characteristics and performance are very different than insoluble resistant starches.