Resistant starch

Resistant starch (RS) is starch, including its degradation products, that escapes from digestion in the small intestine of healthy individuals.

Resistant starch is a type of carbohydrate that resists digestion in the small intestine and travels to the large intestine where it ferments and produces short-chain fatty acids. 

This process is similar to the fermentation of dietary fiber. 

Resistant starch can be found in foods like potatoes, green bananas, lentils, and whole grains. 

It has been linked to several health benefits, including improved insulin sensitivity, reduced inflammation, and improved gut health.

Some benefits of consuming resistant starch:

Improved digestive health: Resistant starch helps to promote bowel regularity by increasing fecal bulk and creating an environment that supports the growth of beneficial bacteria in the gut.

This can help prevent constipation, diarrhea, and other digestive issues.

Blood sugar management: Resistant starch has been shown to improve blood sugar control by reducing the glycemic response of foods.

By slowing down carbohydrate absorption, resistant starch can help prevent spikes in blood sugar levels after a meal.

Increased satiety: Resistant starch can help increase feelings of fullness, thereby reducing hunger and food intake.

This can be beneficial for weight management.

Improved insulin sensitivity: Resistant starch can increase insulin sensitivity, which is particularly important for people with insulin resistance or type 2 diabetes.

5Lowered risk of colorectal cancer: Resistant starch has been shown to have protective effects against the development of colorectal cancer.

This may be due to its ability to promote a healthy gut microbiome and improve digestive health.

Reduced inflammation: Resistant starch has been shown to reduce inflammation, which is associated with a range of chronic diseases, including cardiovascular disease, type 2 diabetes, and Alzheimer’s disease.

Overall, incorporating resistant starch into the diet may provide a range of health benefits.

Foods high in resistant starch include legumes, oats, green bananas, and cooked and cooled potatoes and rice.

Resistant starch occurs naturally in foods, but it can also be added as part of dried raw foods, or used as an additive in manufactured foods.

Some types of resistant starch 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 has similar physiological effects as dietary fiber, behaving as a mild laxative and possibly causing flatulence.

Resistant starch is currently considered to be one of three starch types: rapidly digested starch, slowly digested starch and resistant starch.

Each starch type of may affect levels of blood glucose.

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 the gut microbiota.

The 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 in 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.

 Modest amounts of gases such as carbon dioxide, methane, and hydrogen are also produced in intestinal fermentation. 

One study estimated that the acceptable daily intake of resistant starch may be as high as 45 grams in adults, an amount exceeding the total recommended intake for dietary fiber of 25–38 grams per day.

When isolated resistant starch is used to substitute for flour in foods, the glycemic response of that food is reduced.

There is limited evidence that resistant starch can improve fasting glucose, fasting insulin, insulin resistance and sensitivity, especially in individuals who are diabetic, overweight or obese.

Resistant starch may reduce appetite, especially with doses of 25 grams or more. 

Resistant starch may reduce low-density cholesterol.

There is limited evidence that resistant starch may improve inflammatory biomarkers, including interleukin-6, tumor necrosis factor alpha, and C-reactive protein.

Resistant starch does not appear to reduce colorectal cancer risk.

Starch is stored in tightly packed granules, consisting of layers of amylose and amylopectin.

The size and shape of the starch granule varies by botanical source: the average size of potato starch is approximately 38 micrometers, wheat starch an average of 22 micrometers and rice starch approximately 8 micrometers.

Maize / corn 5-30 micrometers

Waxy maize 5-30 micrometers

Tapioca 4-35 micrometers

Potato 5-100 micrometers

Wheat 1-45 micrometers

Rice 3-8micrometers

Compound granules 68-78

High amylose maize5-30

Raw starch granules resist digestion, e.g., raw bananas, raw potatoes. 

Its resistance to digestion does not depend on the amylose or amylopectin content, but rather the structure of the granule protecting the starch.

When starch granules are cooked, water is absorbed into the granule causing swelling and increased size, and amylose chains can leak out as the granule swells. 

The viscosity of the solution increases as the temperature is increased.

The gelatinization temperature is defined as the temperature at which maximum gelatinization or swelling of the starch granule has occurred, and is the point of maximum viscosity. 

Further cooking bursts the granule apart completely, releasing all of the glucose chains. 

Viscosity is reduced as the granules are destroyed. 

The glucose chains can reassociate into short crystalline structures, which typically involves rapid recrystallization of amylose molecules followed by a slow recrystallization of amylopectin molecules in a process called retrogradation.

Plants produce starch with different structures and shapes which may affect digestion. 

Smaller starch granules are more available to enzyme digestion because the larger percentage of surface area increases the enzyme binding rate.

Starch consists of amylose and amylopectin which affect the textural properties of manufactured foods. 

Cooked starches with high amylose content generally have increased resistant starch.

Resistant starch (RS) are starch digestion products that are not digested and absorbed in the stomach or small intestine and pass on to the large intestine. 

RS has been categorized into five types:

RS1 – Physically inaccessible or undigestible resistant starch, such as that found in seeds or legumes and unprocessed whole grains. 

This starch is bound within the fibrous cell walls.

RS2 – Resistant starch is inaccessible to enzymes due to starch conformation, as in green bananas, raw potatoes, and high amylose corn starch.

RS3 – Resistant starch that is formed when starch-containing foods, such as rice, potatoes, that 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.

RS5 – Starches that are complexed with lipids.

Processes that break down structural barriers to digestion reduce resistant starch content, with greater reductions resulting from processing: Whole grain wheat may contain as high as 14% resistant starch, while milled wheat flour may contain only 2%.

Resistant starch content of cooked rice may decrease due to grinding or cooking.

Processing that increases resistant starch content: If cooking includes excess water, the starch is gelatinized and becomes more digestible. 

However, if these starch gels are then cooled, they can form starch crystals resistant to digestive enzymes.

Type RS3 or retrograded resistant starch occur in cooked and cooled cereals or potatoes.

Cooling boiled potatoes overnight at 4°C (39.2°F) increases the amount of resistant starch by a factor of 2.8.

High amylose varieties of corn, wheat, barley, potato and rice have been bred to increase the resistant starch content.

These breeding changes allow survival of baking and mild extrusion processing, enabling  the delivery of resistant starch in processed foods.

Resistant starch is both a dietary fiber and a functional fiber, depending on whether it is naturally in foods or added.

Food Serving size 

(1 cup is ≈227 grams) Resistant starch 

(grams) grams per 100 grams (%)

Banana flour, from green bananas 1 cup, uncooked 42–52.8 ~20.9 (dry)

Banana, raw, slightly green 1 medium, peeled 4.7

High amylose RS2 corn resistant starch 1 tablespoon (9.5 g) 4.5 47.4 (dry)

High amylose RS2 wheat resistant starch 1/4 cup (30 g) 5.0 16.7

Oats, rolled 1 cup, uncooked (81.08 g) 17.6 21.7 (dry)

Green peas, frozen 1 cup, cooked (160 g) 4.0 2.5

White beans 1 cup, cooked (179 g) 7.4 4.1

Lentils 1 cup cooked (198 g) 5.0 2.5

Cold pasta 1 cup (160g) 1.9 1.2

Pearl barley 1 cup cooked (157 g) 3.2 2.03

Cold potato 1/2″ diameter 0.6 – 0.8

Oatmeal 1 cup cooked (234 g) 0.5 0.2

Dietary Fiber definitions: functional fiber as isolated, nondigestible carbohydrates that have beneficial physiological effects in humans.

Dietary fiber defined as nondigestible carbohydrates and lignin that are intrinsic and intact in plants.

It has been estimated that average resistant starch intake in developed countries ranges from 3–6 grams/day for Northern Europeans, Australians and Americans, 8.5 grams/day for Italians and 10–15 grams/day in Indian and Chinese diets.

The higher consumption of starch-containing foods like pasta and rice likely accounts for higher intake of resistant starch in Italy, India and China.

The  traditional African diet is high in resistant starch.

Rural black South Africans consume an average of 38 grams of resistant starch per day: cooked and cooled corn porridge and beans.

RS2 resistant starch from high amylose wheat and high amylose corn can be baked into foods, usually replacing flour or other high glycemic carbohydrates.

Isolated and extracted resistant starch and foods rich in resistant starch have been used to fortify foods to increase their dietary fiber.

Typically, food fortification utilizes RS2 resistant starch from high amylose corn or high amylose wheat, 

RS3 resistant starch from cassava and RS4 resistant starch from wheat and potato, can survive varying degrees of food processing without losing their resistant starch content.

Resistant starch has a small particle size, white appearance, bland flavor and low water-holding capacity.

Resistant starch typically replaces flour in foods such as bread and other baked goods, pasta, cereal and batters because it can produce foods with similar color and texture of the original food.

Resistant starch  also has also been used for its textural properties in imitation cheese.

Some types of resistant starch are used as dietary supplements in the United States. 

RS2 from potato starch and green banana starch maintain their resistance as long as they are consumed raw and unheated; If they are heated or baked, these types of starch may become rapidly digestible.

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