About Resistant Starch
Not all fiber is the same!
When it comes to eating fiber, just about everyone could do a lot better. In fact, most people could significantly increase their current fiber intake and still not reach the recommended targets of between 25 grams (for women) and 38 grams (for men) each day. The World Health Organization currently recommends consumption of foods containing >25 grams of total dietary fiber/day. In fact, the WHO has identified dietary fiber as the only dietary ingredient with “Convincing Evidence” showing a protective effect against weight gain and obesity.1
Traditionally, people get their fiber from sources like whole grains, produce and beans. Now there’s an exciting new way to reach these goals and gain a wide variety of additional important help benefits – resistant starch.
Without changing their diets, without sacrificing taste and convenience, consumers can obtain additional fiber and other valuable health advantages by eating popular foods like breads, pasta and cereal containing this natural fiber from corn.
This page explains what resistant starch is, its many health benefits and its unique advantages over other fiber sources.
What is resistant starch and what is it “resisting”?
Resistant starch is starch that “resists” digestion in the small intestine. In fact, resistant starches have been defined as “the sum of starch and products of starch digestion not absorbed in the small intestine of healthy individuals.”2
In general, carbohydrates can be divided into two groups: those that are digested in the small intestine and those that are not.
- Sugars and most starches fall into the first group. They are rapidly digested and absorbed, and subsequently used for short-term energy needs or stored. These are referred to as available, digestible or glycemic carbohydrates.
- Resistant starch and dietary fiber constitute the second group. By definition, they pass through the small intestine and provide no short-term energy but have a variety of physiological effects in (and emanating from) the large intestine. Natural resistant starches are fermented like some dietary fibers and provide long-term energy. These are referred to as non-glycemic carbohydrates.
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Is resistant starch new?
Not at all. Resistant starches have always been with us. But it is only recently that we have begun to understand them. For many years, scientists thought that all starches were fully digested. Today, more sophisticated research techniques have disclosed that some starches move undigested into the large intestine where, through fermentation, they take on many of the roles – and provide the benefits of – other carbohydrates long recognized as dietary fiber.
For the past two decades, there has been a steady increase in our knowledge of the sources, uses and physiological effects of resistant starch. However, it has only been in the past decade that the use of ingredients with high resistant starch content has occurred in foods, initially in Australia, but now throughout the world. This has allowed consumers everywhere to take advantage of the important health advantages of this ingredient.
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Are all resistant starches the same?
No they’re not! Today’s resistant starches are typically categorized into four classes:
RS1 Physically inaccessible or digestible resistant starch, such as that found in seeds, 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 (i.e. HI-MAIZE®).
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 (i.e. NOVELOSE®).
RS4 Selected chemically-modified resistant starches, not found in nature.
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Which type of fiber is resistant starch?
It’s long been thought that there were only two kinds of fiber – soluble and insoluble. Over the last 20 years nutrition research has demonstrated that there is a third kind – resistant starch. All three kinds of fiber are essential to health.
· Soluble Fiber (e.g., pectins, gums, mucillages, and some hemicellulose): Helps lower blood cholesterol levels and controls blood sugar. It is found in fresh and dried fruit, vegetables, oats, legumes and seeds. Soluble fibers can be fermented by the bacteria in the large intestine, and may promote intestinal health (known as a “prebiotic” fiber).
· Insoluble Fiber (e.g., cellulose, lignan and hemicellulose): provides bulking and helps keep us “regular.” It is found in whole grain bread, wholegrain cereals, fruits, vegetables, unprocessed bran and wheat germ.
· Resistant Starch – These are starches that escape digestion in the small intestine. Natural resistant starch (RS2) is insoluble, is fermented in the large intestine and is a prebiotic fiber, providing some of the health benefits of both soluble and insoluble fiber – plus some unique advantages of its own. The characteristics of other types of resistant starches vary and the benefits are largely unknown.
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Is resistant starch in the foods we already eat?
Resistant starch is naturally present in foods such as unprocessed whole grains, legumes, cooked-and-chilled pasta, cold rice (as in sushi) and potato salad. As researchers learn more and more about its health benefits and ease of use, resistant starch is quickly gaining attention as an ideal way to add fiber to a wide range of foods. Many public health authorities and food organizations such as the Food and Agricultural Organization, the World Health Organization3, the British Nutrition Foundation4 and the U.S. National Academy of Sciences5 now recognize resistant starch as a beneficial carbohydrate and a type of dietary fiber.
Currently, there is only one commercially-available natural resistant starch from corn on the market – HI-MAIZE. This natural fiber made from corn can be added to breads, cereals, pasta, nutrition bars and more.
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How is resistant starch made?
Natural resistant starch used as food ingredients begin with high amylose corn hybrids produced through traditional plant breeding. Other naturally occurring sources do not have the process tolerance offered by high amylose corn. A mild heat/moisture treatment helps to align the amylose chains within the natural starch granule. Because it retains its natural granule structure, it is a Type 2 Resistant Starch (RS2).
Retrograded resistant starches used as food ingredients can also be made from high amylose corn. An enzyme treatment combined with a mild heat/moisture treatment helps align the amylose chains outside of the starch granule. Because it is “retrograded” or crystallized after the starch granule has been disrupted (known as “gelatinization”), it is a Type 3 Resistant Starch (RS3).
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What are the health benefits of RS2 resistant starch?
There is substantial research on the health benefits of RS2 resistant starches from high amylose corn, including more than 200 published, peer-reviewed studies that indicate benefits in intestinal/colonic health as well as metabolically important benefits in glycemic management and energy.
Of the 200 nutritional studies mentioned above, more than 70 studies in humans using high amylose corn (RS2), show that RS2 starches contribute specific health benefits. Just a few examples:
This substantial amount of data provides a high level of confidence in the benefits that could be obtained through the consumption of RS2 resistant starches. For more information on research on resistant starches from high amylose corn, see the Clinical Studies section of this website
- A recently published clinical trial by Dr. Joanne Slavin and her colleagues at the University of Minnesota demonstrated that eating food made RS2 resistant starch and RS3 resistant starch from high amylose corn had more of an impact on satiety than other types of fibers (corn bran, barley beta-glucan, and polydextrose). This study suggests that added fibers will not impact satiety uniformly and that the type of fiber must be carefully considered in new product development.
- Several studies have been published by Dr. Denise Robertson and her colleagues at the Oxford Lipid Metabolism Group and the University of Surrey (UK). The most recent study, (Bodinham PNAS 2008) found that that dietary consumption of HI-MAIZE resistant starch resulted in 10% fewer calories being consumed in the following 24 hours. There was also significantly lower energy intake at the ad libitum test meal.
- Dr. Anne Nilsson and her colleagues at Lund University (Denmark) found that when resistant starch from HI-MAIZE resistant starch and from barley kernels (another natural source of resistant starch) was consumed in the evening meal, it resulted in improved glucose tolerance, lowered inflammatory biomarkers and increased satiety after a standardized, high glycemic breakfast the following morning.
- Numerous studies demonstrate that RS2 and RS3 resistant starches from high amylose corn promotes intestinal/colonic health through their fermentation and action as prebiotic fibers. They encourage the growth of health-promoting bacteria, reduce pH and increase the production of butyrate via fermentation. Buytrate, a short-chain fatty acid, is important for colonic health and has been shown to have many health-promoting properties.
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How much resistant starch should we consume daily?
Public health authorities and governments have not yet set recommended levels for resistant starch consumption. The Joint Food and Agricultural Organization of the United Nations/World Health Organization Expert Consultation on Human Nutrition stated "Perhaps the greatest impact of recent knowledge is our growing understanding of the diverse physiological roles that carbohydrates have, depending to a great extent on the site, rate, and extent of their digestion and fermentation in the gut…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
In Australia, where resistant starch has been most extensively studied, the Division of Human Nutrition at CSIRO (Commonwealth Scientific and Industrial Research Organization – Australia’s national scientific research organization) advises that "... intakes in the order of 20 grams per day of resistant starch may be needed to obtain some of the bowel related benefits.” 7
Resistant starch intakes vary greatly around the world. Currently most developed countries consume between 3-7 grams of resistant starch per day.
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Is there an upper limit for resistant starch consumption?
The entire daily-recommended intake of dietary fiber (>25 grams according to the World Health Organization) could be consumed from natural resistant starch without digestive side effects. Clinical studies have shown that high levels of RS2 resistant starch from high amylose corn (even those exceeding the recommended intake of dietary fiber) can be consumed with modest or no digestive side effects.
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How many calories does resistant starch have?
RS2 resistant starch actually delivers fewer calories than flour and is a valuable part of diets designed for maintaining healthy weight. The energy value has been estimated to be between 2 and 3 calories (8-12 kilojoules), depending on each individual’s metabolism. By comparison, digestible starch – like flour -- delivers 4 calories (16 kilojoules).
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How is resistant starch labeled?
Consumers won’t usually see “resistant starch” in a list of food ingredients. Different types of resistant starch must be labeled in different ways as food ingredients. Natural RS2 analyzes as dietary fiber and is listed as fiber on the nutritional information on product labels. The type-2 resistant starches are usually designated simply as “resistant cornstarch” or “corn starch” on food product labels. For other classes of resistant starch, the label varies. Type 3 resistant starches can be labeled as “maltodextrin”, or "resistant cornstarch". Chemically modified starches (RS4) are labeled as “modified food starch.” Some products of starch degredation (dextrins) may be considered resistant starch and may be labeled as "dextrin".
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What foods can feature resistant starches?
Resistant starches have been used successfully in breads, cakes, pasta, cereals, snacks and other baked goods. They can also be added to some beverages, mashed potatoes, casseroles and other mixed entrees.
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What advantages does RS2 resistant starch offer, over other fiber sources?
Resistant starch offers three main advantages over other fiber-fortification options like bran, cellulose and inulin.
1) RS2 resistant starch offers unique health benefits, including intestinal/colonic health and metabolically important benefits in glycemic management and energy. Other non or less fermentable fibers such as wheat bran and cellulose cannot match RS’s benefits because many of the benefits stem from RS’s fermentation in the large intestine.
2) Resistant starch is “invisible” in foods – it doesn’t affect taste and texture like other insoluble fiber sources often do.
3) Resistant starch has unique functional properties yielding high quality foods, and is especially appropriate for grain-based low- and moderate-moisture foods because it commonly replaces flour. Its physical properties, particularly its low-water-holding capacity, enable it to be used to provide good food processing characteristics and desirable textural attributes such as crispness and expansion when compared to foods of similar fiber content.
4) Due to the slow fermentation characteristic of resistant starch’s insoluble structure, RS2 can be consumed at significantly higher quantities without digestive side effects common to soluble fibers like inulin and fructo-oligosaccharides.
1. World Health Organization, Joint WHO/FAO Expert Consultation “Diet, Nutrition and the Prevention of Chronic Diseases” 2003, WHO Technical Report Series 916.
2. Asp, N-G. Resistant Starch. Proceedings from the second plenary meeting of EURESTA: European FLAIR Concerted Action No.11 on the physiological implications of the consumption of resistant starch in man. Preface. European Journal of Clinical Nutrition, 1992 46 Suppl 2 S1
3. Carbohydrates in Human Nutrition, Joint FAO/WHO Expert Consultation in Human Nutrition, April 1997
4. Nugent, A.P., Health properties of resistant starch, 2005, British Nutrition Foundation Nutrition Bulletin, Vol. 30, No. 1:27-54.
5. “Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fatty Acids, Cholesterol, Protein and Amino Acids (Macronutrients)” The Institute of Medicine of the National Academies, September 5, 2002.
6. de Haen, H. (FAO Assistant Director-General, Economic & Social Dept), Carbohydrates in Human Nutrition, FAO Food & Nutrition Paper – 66. A Joint FAO/WHO Expert Consultation on Human Nutrition, Rome, April 14-18, 1997.
7. Baghurst PA, Baghurst KI, Record SJ, Dietary fibre, non-starch polysaccharides and resistant starch – a review. Food Australia, 1996 Vol 48, No. 3:S1-S35.