Resistant starches are complex carbohydrates that resist digestion by your small intestines. They enter your large intestine, or colon, intact and are then excreted. Resistant starch is sometimes isolated from its original food source and used as a functional fiber. When included as an ingredient, functional fibers fortify processed foods, thus boosting their fiber content. There are four types of resistant starch.
Resistant Starch Type 1
Resistant starch type 1, or RS1, can be partially digested by your small intestine in its natural form, or totally digested if it is milled, according to Pei Tze Ang of the University of Nebraska-Lincoln. When you chew RS1, you're partially breaking down the starch and making it easier for your small intestine to digest it. This type of resistant starch resists digestion because in its natural form it is trapped inside a non-digestible matrix formed by the cell walls of the plants from which it is derived. RS1 is found in grains, seeds and legumes that are whole or partially milled. It is also found in pasta made from these grains, seeds and legumes.
Resistant Starch Type 2
Resistant starch type 2, or RS2, undergoes very little digestion in the small intestine when consumed raw, and the scant amount of digestion that does happen occurs very slowly. This form of starch occurs in a granulated form that resists digestion. When resistant starch type 2 is processed or cooked, however, it becomes completely digestible. Resistant starch type 2 is found in high amylose corn starch, which is derived from non-genetically modified specialty maize varieties. It is also found in raw green bananas and raw potatoes.
Resistant Starch Type 3
Resistant starch type 3, or RS3, is partially digestible by your small intestine, but digestion occurs very slowly. Cooking and cooling certain foods creates this type of starch. When those foods are reheated, their digestibility increases. Foods containing RS3 include potatoes that have been cooked and cooled, bread and corn flakes. RS3 is also found in many foods that have been prepared from RS2 through processes involving heat and the addition of moisture.
Resistant Starch Type 4
Resistant starch type 4, or RS4, consists of starches that have been chemically modified or industrially processed to resist digestion by blocking the activity of digestive enzymes. This type of resistant starch is used as an ingredient in processed foods such as breads and cakes. According to a study published in the "Journal of Nutrition and Metabolism" in 2010, a type of RS4 derived from wheat was found to be effective at lowering blood glucose levels.
References
- University of Nebraska-Lincoln; Adaptation and Validation of Existing Analytical Methods for Monitoring Prebiotics Present in Different Types of Processed Food Matrices; Pei Tze Ang; 2011
- "Journal of Nutrition and Metabolism; Different Types of Resistant Starch Elicit Different Glucose Reponses in Humans; Mark D. Haub, et al.; January 2010
- Plantic: High Amylose Corn Starch
- University of Colorado Extension; Dietary Fiber; Jennifer Anderson, et al.; December 2010
