Resistant starch is a type of starch that resists digestion in the small intestine and reaches the large intestine intact. It is found in various foods such as grains, legumes, fruits, and vegetables, and can also be produced through food processing. Resistant starch has been associated with various health benefits, including improved glycemic control, increased satiety, and improved gut health.
Definition
Resistant starch (RS) is a type of dietary starch that resists digestion in the small intestine and reaches the large intestine intact. This is due to its chemical structure, which makes it resistant to the action of digestive enzymes. Instead, it undergoes fermentation by the microbiota in the large intestine, producing short-chain fatty acids and other metabolites that have various health benefits. RS is classified into four types based on its physical and chemical properties: RS1, which is physically inaccessible starch; RS2, which is resistant starch granules; RS3, which is retrograded starch; and RS4, which is chemically modified starch. Dietary sources of resistant starch include whole grains, legumes, some fruits and vegetables, and cooled or reheated starchy foods.
Properties
Resistant starch (RS) has several properties that distinguish it from other types of starch:
- Resists digestion: As the name suggests, RS resists digestion in the small intestine, reaching the large intestine intact.
- Fermentable: RS is fermented by the microbiota in the large intestine, producing short-chain fatty acids (SCFAs) such as butyrate, propionate, and acetate.
- Low glycemic index: RS has a lower glycemic index than other types of starch, meaning it causes a slower and more sustained increase in blood glucose levels.
- Low calorie content: RS has a lower calorie content than other types of starch, as it is not fully digested and absorbed in the small intestine.
- Prebiotic: RS promotes the growth of beneficial bacteria in the large intestine, such as bifidobacteria and lactobacilli, which have been associated with various health benefits.
- May reduce the risk of chronic diseases: Studies have suggested that RS intake may reduce the risk of several chronic diseases, such as colon cancer, type 2 diabetes, and cardiovascular disease.
- May increase mineral absorption: Some types of RS have been shown to increase the absorption of minerals such as calcium and magnesium.
- Heat-stable: Unlike other types of dietary fiber, RS is resistant to heat and can retain its properties even when cooked or processed.
Types
There are generally considered to be five types of resistant starch:
- RS1: Physically inaccessible starch, which is trapped within the food matrix in proteins, cell wall materials, and other physical barriers in whole or partly milled grains, tubes, and seeds.
- RS2: Raw granular starch with a B- or C-type polymorph, which is comprised of native, uncooked granules with B- or C-type polymorphs, such as those found in raw potatoes, unripe banana starches, and high-amylose maize starches.
- RS3: Retrograded starch, which is first gelatinized in hot water and then cooled for retrogradation, during which the two polymer chains reassociate to form double helices stabilized by hydrogen bonds, making the structure more resistant to enzymatic hydrolysis.
- RS4: Chemically modified starch, which includes the modifications of esterification, etherification, or cross-linking.
- RS5: Amylose-lipid complex and resistant maltodextrin, which has been proposed as two different components involving amylose-lipid complexes and resistant maltodextrins obtained by subjecting native starch to sequential applications of pyroconversion and enzymatic hydrolysis.
Production
Resistant starch can be produced through several methods, including:
- Physical processing: This method involves physically processing starch-containing foods to create resistant starch. For example, cooking and cooling starchy foods, such as potatoes or rice, can convert some of the digestible starch to resistant starch.
- Chemical modification: Resistant starch can also be produced by chemically modifying starch. The most common method is cross-linking, which involves chemically bonding starch molecules to create a more complex structure that resists digestion by enzymes in the small intestine.
- Enzymatic modification: Enzymes can also be used to produce resistant starch. For example, some enzymes can break down amylose and amylopectin molecules into smaller chains that are resistant to digestion.
- Genetic modification: Scientists have also developed genetically modified crops, such as high-amylose corn, that naturally produce more resistant starch.
- Extraction from natural sources: Some natural sources, such as green bananas or plantains, contain high amounts of resistant starch that can be extracted and used in food products.
The production of resistant starch can vary depending on the specific method used and the desired application.
Applications in food
Resistant starch (RS) has several applications in foods. Here are a few examples:
- Baked goods: RS can be added to bread, muffins, and other baked goods to increase their fiber content and improve their nutritional profile. It can be added directly to the dough or used as a coating on the surface of the baked product.
- Pasta and noodles: RS can be added to pasta and noodles to improve their texture, reduce stickiness, and increase their resistant starch content. RS can also be used to coat the surface of pasta and noodles to prevent them from sticking together during storage and cooking.
- Snacks and cereals: RS can be added to snacks and cereals to increase their fiber content and improve their nutritional profile. It can be used as a coating on the surface of the snack or cereal, or it can be incorporated directly into the product.
- Beverages: RS can be added to beverages such as smoothies and shakes to increase their fiber content and improve their nutritional profile. RS can be used as a thickening agent or added directly to the beverage.
- Dairy products: RS can be added to dairy products such as yogurt and cheese to improve their texture and increase their fiber content. RS can be added directly to the product or used as a coating on the surface of the product.
Overall, RS can be added to a wide range of foods to improve their nutritional profile, increase their fiber content, and improve their texture and other functional properties.
The Health Effects
Resistant starch has been studied extensively for its potential health benefits. Some of the reported health effects of consuming resistant starch include:
- Improved digestive health: Resistant starch has been shown to improve gut health by increasing the production of short-chain fatty acids (SCFAs) in the colon, which promotes the growth of beneficial bacteria in the gut.
- Lowered glycemic response: Resistant starch has a lower glycemic response than digestible carbohydrates, which can help regulate blood sugar levels and reduce the risk of type 2 diabetes.
- Increased satiety: Resistant starch can increase feelings of fullness and satiety, which may lead to reduced calorie intake and weight loss.
- Improved lipid profile: Resistant starch has been shown to improve lipid profiles by reducing total cholesterol, LDL cholesterol, and triglycerides.
- Reduced inflammation: Resistant starch can reduce inflammation by decreasing the production of pro-inflammatory cytokines.
- Reduced risk of colon cancer: Resistant starch has been associated with a reduced risk of colon cancer due to its ability to promote the growth of beneficial bacteria and decrease inflammation in the colon.
It’s important to note that not all studies have shown these health benefits, and more research is needed to fully understand the effects of resistant starch on human health. Additionally, the health effects may vary depending on the type and amount of resistant starch consumed.