What is Resistant Starch?
Resistant starch (RS) a type of carbohydrate that isn?t readily digestible. It is generally thought to pass through the small intestine undigested, making it to the large intestine where it is slowly fermented. Once in the large intestine, it feeds bacteria and may provide numerous health benefits.
RS is metabolized about 5-7 hours after consumption. This is much slower than normally cooked starch, which is digested right away. Physiologically, RS behaves similarly to soluble fiber, with effects such as improved bowel health and glycemic control, lowered cardiovascular disease risk factors, and improved colonic health.
Resistant starch is unique in that it is not inherently indigestible and is not a fixed entity. The degree of digestibility and effects of consumption are determined by the digestive function of the individual and the form, processing and
storage of the RS source itself.
There are 4 commonly recognized forms of resistant starch:
RS1 – Physically inaccessible to digestion because it?s trapped within the food itself. Some examples of foods with RS1 are seeds, legumes, and unprocessed whole grains.
RS2 – Sometimes referred to as ungelatinized starch, RS2 is resistant to digestion before cooking. The structure of the starch itself makes it resistant to digestion. It is present in foods like plantains, unripe bananas, and uncooked potatoes.
RS3 – Retrograded starch – found in some starchy foods that have been cooked and cooled. RS3 remains even when food is reheated.
RS4 – Chemically modified starch that is not found in nature.
The term prebiotic refers to any food ingredients or nutrients, usually carbohydrates, that pass through the upper digestive tract without being digested and go on to be fermented by bacteria in the lower digestive tract. This activity changes both the composition and activity of the gut microbiome. RS acts as a prebiotic to help beneficial microorganisms such as Bifidobacterium move through the small intestine and make it to the colon. The resistant starch creates a protective environment for probiotics and carries the bacteria through the gastrointestinal tract, protecting it from damage. Once in the large intestine, RS serves as a substrate to promote the growth of probiotics. It appears to selectively increase populations of Bifidobacterium and Bacillus species.
RS can have a synergistic effect when combined with other fermentable fibers such as fructooligosaccharides (FOS). Together, these prebiotics can increase the growth of a wider variety of bacteria and have beneficial effects such as improved absorption of minerals such as zinc, calcium, magnesium, and iron.
Butyrate and Cancer Prevention
One of the suspected reasons for the benefits of RS is its contribution to increased butyrate production by bacteria. Butyrate is associated with improved colonic health and lowered colorectal cancer risk. Indigestible carbohydrates in general promote butyrate production, but RS appears to be uniquely beneficial in its ability to promote a higher proportion of butyrate production.
Fermentation of RS by anaerobic bacteria in the colon creates short chain fatty acids (SCFAs), primarily acetic, propionic, and butyric acids, which are known to lower the pH of the lumen. Lower pH environments are less prone to the development of cancerous tumors. Presence of butyrate in the large intestine is inversely associated with DNA damage to colonocytes. Butyrate prevents large intestinal cells from becoming malignant and can induce apoptosis in cancerous cells.
RS consumption may also have implications for the prevention of cancers other than colorectal cancer. In one study, breast tumor growth was inhibited and tumor size was reduced in mice fed RS and fructo-oligosaccharides. There is more research forthcoming with regard to the potential for RS to help with cancer prevention and for use as an adjunct to existing treatment options.
There is some compelling evidence for the ability of resistant starch to assist with weight management. Some of this may be attributed to reduced glucose response, improved insulin sensitivity, and increased satiety following RS-containing meals. Experiments have shown an overall decrease in food intake over a 24-hr period following RS consumption. The decrease is likely due at least in part to the production of the appetite-suppressing hormones glucagon-like peptide 1 and peptide YY when RS is fermented in the large intestine.
RS also significantly lowers insulin levels following consumption of other starches, even when the starches are consumed during later meals. Consuming resistant starch following a weight loss regimen may also help to prevent fat regain. Lastly, there is evidence that replacing carbohydrates with RS can reduce fat accumulation via increased lipid oxidation following meals.
Triglycerides – There is evidence that consumption of resistant starch can help to lower triglyceride levels, which is pretty universally seen as a health benefit.
Gallstones – While digestible starch is thought to contribute to the formation of gallstones, resistant starch lowers their incidence.
Safe for SIBO?
There are conflicting reports as to whether consumption of resistant starch may increase problems associated with SIBO. I think this is a legitimate concern. There are certain species of bacteria that are known to degrade resistant starch in the large intestine. In SIBO, these and other bacteria migrate up into the small intestine, so it wouldn?t be surprising if those bacteria digest RS in the small intestine and perpetuate SIBO symptoms. RS is expected to pass undigested through the small intestine, but if RS-digesting bacteria have migrated into the small intestine, there is reason to believe that it could be digested there as well and contribute to problems associated with SIBO.
Including RS in the Diet
There are a variety of ways to add whole food resistant starch to your diet. Green bananas and raw green plantains are great sources of RS2. If green bananas aren?t your favorite, you can throw them in a smoothie to minimize the starchiness. I slice up green plantains and dehydrate them into chips to snack on alone or dip in guacamole.
Another convenient source of resistant starch is cooked and cooled white potatoes. A good rule of thumb is to bake potatoes then stick them in the fridge overnight. Once cooked and cooled, the potatoes can be reheated and will retain their RS content. I know some people who have had found benefits from consuming unmodified potato starch, usually a tablespoon or so stirred into water. Cooked and cooled white rice also contains?a good amount of resistant starch.
If legumes are part of your diet, they can also be a good source of RS. In fact, high RS1 content may be one reason diets high in legumes have been shown to be beneficial. I would actually venture to guess that it?s the primary reason. If you do consume legumes, I strongly suggest properly preparing them via soaking and fermenting if possible.
RS is also added to processed food products such as cookies and bread. However, I do not consider this a good source of RS, because it involves eating processed ?foods? that I would never advocate eating. There are some really great whole food sources of RS, so I see no reason to eat RS-supplemented processed foods.
For a more complete list of foods that contain resistant starch, check out this chart from Free the Animal.
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Fuentes-Zaragoza et al.(2011). Resistant starch as a prebiotic: A review. Starch, 63, 406-415.
Haenen et al. (2013). A diet high in resistant starch modulates microbiota composition, SCFA concentrations, and gene expression in pig intestine. The Journal of Nutrition, 143, 274-283.
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Higgins et al. (2011). Resistant starch and exercise independently attenuate weight regain on a high fat diet in a rat model of obesity. Nutrition and Metabolism, 8(49), 1-15.
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