Resistant starch is a type of starch that is not digested in the small intestine. Instead, this starch is digested in the large intestine, much later in the digestive process. Because of this, resistant starch has properties that are very similar to those of dietary fiber.
This type of starch has many health benefits. One is that, because this starch behaves in a fashion similar to fiber, eating foods containing resistant starch can improve digestion and help maintain bowel movement regularity. Worldwide, many countries recommend an average daily fiber intake of between 25 and 30 grams; eating foods containing resistant starches can help boost fiber intake to the recommended level. Resistant starches also are thought to help promote digestive health by encouraging the growth of healthy intestinal bacteria.
Another health benefit of resistant starches is that they help regulate blood sugar. This is because only a small portion of the energy in this type of starch is released in the small intestine in the form of glucose. Much of the energy is released later in digestion, in the large intestine. This helps prevent a spike in blood sugar after eating and helps prevent sudden decreases in blood sugar between meals.
Most naturally occurring resistant starch can be found in foods that are traditionally thought of as starchy. These foods include navy beans, lentils, oatmeal, whole grains, wholegrain bread products and pearl barley. Cold pasta and cold potatoes also are good sources. Bananas are one of the best naturally occurring sources of this type of starch and are an even richer source when eaten while green.
These different food sources help illustrate the fact that there are several different types of resistant starch. These are categorized according to the types of foods in which they naturally are found. The four types are called RS1, RS2, RS3 and RS4.
RS1 is found mainly in unprocessed whole grains and in seeds and legumes. This type of starch is naturally resistant to small intestine digestion because it is physically inaccessible. This is because the starch is protected by the hard outer coating of the seeds, grains and legumes. RS2 is starch that is resistant in its natural form because the body does not produce enzymes capable of breaking it down. Foods containing RS2 include plantains, green bananas and raw potatoes.
RS3 is found in starchy foods that have been cooked and cooled. These include bread products made of whole grain, certain types of cereal and potatoes and pasta that have been cooled after cooking. The last category, RS4, comprises resistant starches that are not naturally occurring. These are starches that have been modified to increase their resistance to digestion.