Resistant starch

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Resistant starch (RS) is starch that escapes digestion in the small intestine of healthy individuals.^[1] 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 bread, cornflakes and cooked-and-chilled potatoes or retrograded high amylose corn

• 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.

As fiber

Examples of naturally-occurring resistant starch^[2]

Public health and scientific experts widely recognize that a significant gap exists between the amount of fiber most of people consume and the optimal amount of fiber for health and wellness. The National Academy of Sciences of the Institute of Medicine within the United States has recommended a daily intake of 38 grams/day for adult men and 25 grams/day for adult women. Many countries around the world recommend 25-30 grams of fiber/day for their populations. Resistant starch assists in increasing dietary fiber consumption because it can be incorporated into foods without having an impact on the taste or texture of the food.

Health benefits

Many public health authorities and food organizations such as the Food and Agricultural Organization, the World Health Organization^[3], the British Nutrition Foundation^[4] and the U.S. National Academy of Sciences^[5] recognize resistant starch as a beneficial carbohydrate. The Joint Food and Agricultural Organization of the United Nations/World Health Organization Expert Consultation on Human Nutrition stated, "One of the major developments in our understanding of the importance of carbohydrates for health in the past twenty years has been the discovery of resistant starch.”^[6]

Substantial research of natural resistant starches from high amylose corn indicates benefits in intestinal/colonic health as well as metabolically important benefits in glycemic management and energy.^{[citation needed]} Studies have shown that different classes of resistant starch are digested and/or fermented differently and thus must be considered individually.^{[citation needed]}

Weight management

Consumption of foods containing natural resistant starch may positively affect weight management in three ways.

Fiber fortification: When added to foods such as bread, biscuits, sweet goods, pasta, nutritional bars and cereal, resistant starch can increase fiber content without affecting taste or texture. In 2003, the World Health Organization concluded that dietary fiber was the only dietary component that had convincing evidence showing a protective effect against weight gain and obesity^[7]. While the exact mechanisms of fiber protecting against weight gain are still under investigation, its ability to increase satiety and decrease subsequent hunger, along with the altering the secretion of hormones related to food digestion, are considered likely mechanisms.^[8]

Calorie reduction: Resistant starch lowers the caloric content of foods when it is used to replace flour or other rapidly digested carbohydrates. Natural resistant starch delivers between 2-3 kilocalories/gram (8-12 kilojoules/gram) versus 4 kilocalories/gram (16 kilojoules/gram).^[9][10] Consequently, resistant starch is a valuable tool for formulators of reduced-calorie foods.

Lipid oxidation: Resistant starch may help burn fat and may lead to lower fat accumulation. A recent clinical trial with high amylose corn resistant starch showed that it increased fat oxidation after a meal. These findings suggest a possible metabolic effect of resistant starch that may affect body weight.^[11]

Energy management

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Eating foods with natural resistant starch helps balance energy in the hours following a meal, mitigating a drop in blood sugar.

Resistant starch releases part of its energy in the small intestine as glucose, and part of its energy in the large intestine as fermentation by-products.

Resistant starch delivers slowly released energy, providing moderate rises in blood sugar levels. Resistant starch also helps moderate the rapid rise in blood glucose resulting from consumption of processed carbohydrates.

Blood sugar response/glycemic management

Natural resistant starch helps maintain healthy blood sugar levels by increasing insulin sensitivity in healthy people. Incorporation of resistant starch into processed foods (i.e. as a flour substitute) reduces the glycemic impact of that food and increases insulin sensitivity, which research suggests may help to reduce the risk of type 2 diabetes.

Studies suggest continual exposure to elevated levels of insulin as a result of a high glycemic diet may contribute to reduced sensitivity by cells to the insulin (insulin resistance) and a higher risk of diabetes. As insulin resistance increases, the body produces more insulin to maintain adequate blood sugar control. With rising resistance, even more insulin is required, and the body may not be able to keep up or the pancreatic cells producing insulin may stop functioning.

Consumption of natural resistant starch by humans has been shown to result in decreased glycemic response in healthy individuals,^[12] decreased glycemic response in diabetics,^[13], increased insulin sensitivity in healthy individuals.^[14][15], individuals with Type II diabetes ^[16] as well as insulin resistant individuals.^[17]

Digestive/colonic health

Natural resistant starch helps maintain a healthy colon and a healthy digestive system via several mechanisms.

It helps to keep you "regular” with a mild laxative effect.

It encourages the growth of healthy bacteria in the bowel and discourages the growth of potentially harmful bacteria, called “prebiotic fiber.” The fermentation of natural resistant starch reduces intestinal pH and the production of potentially harmful secondary bile acids, ammonia and phenols.^[18]

It helps to keep colon tissue healthy by producing protective compounds called short-chain fatty acids. One of these, called butyrate, is particularly important for colon health because it is the primary energy source for colonic cells and has anti-inflammatory properties that are important for keeping colon cells healthy.^[19][20] In addition, butyrate has anti-carcinogenic properties. Published research has shown that butyrate inhibits the growth and proliferation of tumor cell lines in vitro,^{[citation needed]} induces differentiation of tumor cells, producing a phenotype similar to that of the normal mature cell,^[21] and induces apoptosis or programmed cell death of human colorectal cancer cells.

It contributes to oral rehydration solutions for the treatment of diarrhea.^[22][23]

Gluten free

Resistant starch can act as a replacement for wheat products in foods that are required to be gluten-free. Recent scientific studies suggest that resistant starch’s fermentation within the colon may be important because it produces more butyrate than other fibers tested.^[24] Butyrate, a short-chain fatty acid, has been shown to have anti-carcinogenic properties and anti-inflammatory properties, which may be useful for preventing and/or treating Celiac disease and inflammatory bowel disease.

References

External links

• National Starch Food Innovation
• British Nutrition Foundation
• Carbohydrates in human nutrition - FAO / WHO