Resistant starch (RS) is starch, including its degradation products, that escapes from digestion in the small intestine of healthy individuals. Resistant starch occurs naturally in foods but is also added to foods by the addition of isolated or manufactured types of resistant starch.
Some types of resistant starch (RS1, RS2 and RS3) are fermented by the large intestinal microbiota, conferring benefits to human health through the production of short-chain fatty acids, increased bacterial mass, and promotion of butyrate-producing bacteria.
Resistant starch in various ways has similar physiologic effect as dietary fiber, which is why it functions as a mild laxative and why consuming it can lead to flatulence at high doses.
The concept of resistant starch arose from research in the 1970s and is currently considered to be one of three starch types: rapidly digested starch, slowly digested starch and resistant starch, each of which may affect levels of blood glucose.
The Commission of the European Communities has supported research eventually leading to a definition of resistant starch.
Resistant starch does not release glucose within the small intestine, but rather reaches the large intestine where it is consumed or fermented by colonic bacteria (gut microbiota). On a daily basis, human intestinal microbiota encounter more carbohydrates than any other dietary component. This includes resistant starch, non-starch polysaccharide fibers, oligosaccharides, and simple sugars which have significance to colon health.
The fermentation of resistant starch produces short-chain fatty acids, including acetate, propionate, and butyrate and increased bacterial cell mass. The short-chain fatty acids are produced in the large intestine where they are rapidly absorbed from the colon, then are metabolized in colonic epithelial cells, liver or other tissues. The fermentation of resistant starch produces more butyrate than other types of dietary fibers.
| Examples of naturally occurring resistant starch |
| Food |
Serving size |
Resistant starch
(grams) |
|
Banana flour, from green bananas |
1/4 cup, uncooked |
10.5-13.2 |
| Banana, raw, slightly green |
1 medium, peeled |
4.7 |
| High amylose RS2 corn resistant starch |
1 tablespoon (9.5 g) |
4.5 |
| Oats, rolled |
1/4 cup, uncooked |
4.4 |
| Green peas, frozen |
1 cup, cooked |
4.0 |
| White beans |
1/2 cup, cooked |
3.7 |
| Lentils |
1/2 cup cooked |
2.5 |
| Cold pasta |
1 cup |
1.9 |
| Pearl barley |
1/2 cup cooked |
1.6 |
| Cold potato |
1/2" diameter |
0.6 - 0.8 |
| Oatmeal |
1 cup cooked |
0.5 |
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RS1 – Physically inaccessible or undigestible resistant starch, such as that found in seeds or legumes and unprocessed whole grains.
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RS2 – Resistant starch is inaccessible to enzymes due to starch conformation, as in high amylose corn starch
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RS3 – Resistant starch that is formed when starch-containing foods are cooked and cooled, such as pasta. Occurs due to retrogradation, which refers to the collective processes of dissolved starch becoming less soluble after being heated and dissolved in water and then cooled.
-
RS4 – Starches that have been chemically modified to resist digestion
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