Some good info on resistant starch. Much of this info is found in my book, The Potato Hack: Weight Loss Simplified, but it’s been updated to include new developments in our understanding of resistant starch.
Resistant starch (RS) is starch that does not get digested in the stomach or small intestine and enters the large intestine intact.
This bland definition may be one of the most important things you ever read. This seemingly innocuous substance known as “resistant starch” is a simple solution to a huge problem—the feeding of our intestinal microbiome. For decades now, resistant starch has been exhaustively studied and declared time and again an ideal solution to many of modern society’s health woes. If you find yourself saying, “Why am I just now hearing about this?” you are not alone.
Why Should I Care?
The next question I hope you’ll ask is, “Do I really need resistant starch?” The answer is, “Most likely!”
You may recognize yourself as having the modern, dyspeptic gut: Frequent heartburn, loose stools or constipation, indigestion, smelly gas, GERD, IBS, or worse. You may even have one of the many autoimmune diseases that are running rampant, diabetes, metabolic syndrome, or cancer.
Digestive diseases affect over 70 million people in the US alone! These diseases required 48.3 million ambulatory care visits, 21.7 million hospitalizations, and caused 245,921 deaths in 2009. Total costs for digestive diseases was estimated at $141.8 billion in 2004. And, these stats are getting worse, not better.
It’s estimated that over 90 million Americans use antacids or other digestive upset medicines. Upset stomachs are the number one cause of self-treatment, and those late-night trips to WalMart yield an impressive display of over-the-counter offerings for the modern, dyspeptic human gut.
If none of these describe you, then you have somehow discovered a way to feed your gut flora and you have managed to collect a diverse supply of happy gut bugs—Good Job! But, if you aren’t happy with your gastrointestinal tract or immunity, resistant starch may be just the ticket! There is so much known about resistant starch, yet it is an unknown entity to the people that could benefit from it.
If this article is too long and you don’t want to read it all, the solution is simple: 1-2 spoonfuls of potato starch.
The Revolution that Never Was
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.
— Joint Food and Agricultural Organization of the United Nations/World Health Organization, 1997
The definition normally used for RS is nearly the exact same definition that is used for “dietary fiber,” and a huge reason that RS has escaped the attention of the medical community and the public. RS is not your normal dietary fiber, although it shares similar properties. RS could more technically be called “fermentable starch” or “prebiotic starch,” but since its discovery in 1982, it has been called “resistant starch.” The health implications of RS were not immediately seen, and it’s only been in the last 5-10 years that the huge impact RS can make on the health of humans has been explored. The pioneers in RS as a health booster were pig farmers looking for a way to raise antibiotic-free pigs who found that pigs fed raw potatoes had less infections than pigs fed standard foods. Were it not for this attention, RS may have gone unnoticed to this day.
New FDA Allowable Statements
In December 2016, the FDA ruled that food products that contain high amlyose maize starch (HAMS), or Hi-Maize, the label may display one of the following four statements:
See the full evolution of this FDA health claim here: Regulations.gov, HAMS and Diabetes Docket.
This is just a start for getting RS into the diets of the masses. With this ruling, we should soon see labels that reflect the RS content in foods we buy, hopefully soon more claims will be allowed and more RS sources will be included. Until then, keep in mind that HAMS is about the same thing as raw potato starch and green banana flour.
RS and Fiber
Resistant starch differs from fiber in many ways and should not be confused with the dietary fiber listed on nutrition labels. Let’s look at a standard definition for dietary fiber.
Dietary fiber is the indigestible portion of food derived from plants. There are two main components:
Soluble fiber dissolves in water. It is readily fermented in the colon into gases and physiologically active byproducts, and can be prebiotic and/or viscous. Soluble fibers tend to slow the movement of food through the system.
Insoluble fiber does not dissolve in water. It can be metabolically inert and provide bulking or prebiotic, metabolically fermenting in the large intestine. Bulking fibers absorb water as they move through the digestive system, easing defecation. Fermentable insoluble fibers mildly promote stool regularity, although not to the extent that bulking fibers do, but they can be readily fermented in the colon into gases and physiologically active byproducts. Insoluble fibers tend to accelerate the movement of food through the system.
By this definition, RS does indeed seem to be just another type of dietary fiber—but to call it that, and lump it together with all other dietary fibers was one of the biggest blunders of all time. I hope that the attention RS is getting these days spurs people into action for getting RS classified as an important food ingredient that deserves it’s own special place on nutrition labels and in people’s minds.
In 2003, the World Health Organization attempted to define the perfect diet for world-wide health in their publication: Population nutrient intake goals for preventing diet-related chronic diseases. They made numerous recommendations on dietary fat, sugars, carbohydrates and protein, but when it came to fiber, they admitted defeat in light of new information concerning RS:
The best definition of dietary fibre remains to be established, given the potential health benefits of resistant starch.
This statement, made over 10 years ago, has massive implications for world health and displays the incredible ignorance of modern medicine. At this behest, RS should have become a household word during the last decade. Let’s not wait another decade for the next sound-bite, let’s do something about it NOW.
Four Types of Resistant Starch
RS has been classified into four general types named RS1–RS4, described below:
Type 1 –
RS1 is the physically inaccessible starch that is locked within cell walls such as nuts shells, seed coatings and hulls, and other food matrixes. Milling and chewing can make these starches more accessible and less resistant. While eating whole seeds is very healthy for our digestive systems, RS1 is not an important food source for gut microbes since many of these protective structures cannot be breached and they pass through the body completely undigested. When the coating is breached, RS1 becomes RS2.
Type 2 –
RS2 is in raw starch granules, sometimes called “native starch.” These starch granules are protected from digestion by the structure and composition of the starch granule itself. The structure of the starch granules have an impact on the resistance of the starch—such as the shape of the granule, size of pores or susceptibility of the starch to germinate. Their compact structure prevents digestive enzymes and stomach acid from attacking the starch allowing it to reach the large intestine whole. When RS2 is heated above a certain point, usually around 140 degrees F, it swells and bursts losing it’s RS value completely. RS2 is found in potatoes, green bananas, plantains, taro, cassava, and in most cereal grains. Not all raw starch is resistant starch. Corn and rice starch, for instance are readily digestible for the most part. Potatoes and plantains contain the most resistant starches in nature although there are other good candidates such as mung bean starch and lotus seed starch. In the colon, RS2 is rapidly digested in the caecum and ascending colon, much like high glycemic starch in the small intestine.
Type 3 –
RS3 is retrograded or crystallized starch formed after cooking. This is the starch found in cooked and cooled potatoes, bread crusts, cornflakes, and cold sushi rice. RS3 is non-granular starch that resists digestion. RS3 is interesting because it can withstand heat once it has formed. In most cooking methods, RS2 is destroyed and RS3 takes its place, becoming more dense after repeated heating and cooling cycles. RS3 is the most interesting type of RS and this property to ‘retrograde’ is easily exploited. When fully retrograded, the starch forms a double helix, much like our DNA, and binds water in the interior spaces of the structure. After a few hours in storage, the helices undergo an aggregation and form gels which are thermally stable and resistant to attack by digestive enzymes. In the colon, RS3 acts like slowly digestible/low glycemic starches do in the small intestine—burns long and slow, spreading its influence to the distal ends of the colon.
Type 4 –
RS4 is a man-made, chemically modified or re-polymerized starch. It is not found in nature, but rather manufactured and used widely in the food industry to alter the characteristics of starch to decrease its digestibility. RS4 can be produced by chemical modifications, such as conversion, substitution, or cross-linking, which can prevent its digestion by blocking enzyme access and forming atypical linkages. RS4 does seem to exhibit the same properties as natural RS2 and RS3, so it shouldn’t be dismissed entirely because it is man-made.
Which RS Type is Best?
RS1 is a bit awkward, it’s only as resistant as it’s outer shell, once the shell is breached, it becomes RS2 when liberated from its shell or RS3 if cooked. RS4 is also a bit awkward, it’s a man-made substance and readily used by the food manufacturing industry to add texture and extend shelf life of prepared foods while allowing them to list the food item as “high in fiber.” No one should look to RS4 to fill their need for resistant starch, our ancestors certainly didn’t!
This leaves RS2 and RS3. These are the prehistoric powerhouses that fueled our gut microbes for millions of years. As you can imagine, when we were living a very primitive life we ate our starches raw, consuming only RS2, then later as we learned to cook, RS3 was introduced to the mix. For at least a million years, we likely ate a combination of RS2 and RS3 with hunger and glee. After routine use of controlled fire and larger human settlements, RS3 was undoubtedly used to wean babies, provide consistent meals and energy, and to feed busy hunters and pastoralists. You can bet that at the ancestral hearth, leftovers were not scorned!
Scientific studies show there are slight but significantly noted differences in the two types of RS:
- RS3 was shown to lower fecal ammonia levels better than RS2.
- RS3 was shown to dilute fecal ammonia and other fecal carcinogens whereas RS2 does not unless combined with significant amounts of insoluble fiber to bulk stools.
- RS3 was shown to increase absorption of magnesium, calcium and phosphorous in pigs compared to RS2 (but lowered it in rats).
- RS2 and RS3 have mixed results in initiation and promotion stage in colon carcinogenesis and human colorectal cancer trials however stale cooked maize porridge (RS3) consumed by native Africans was highly associated with protection against colorectal cancer.
- RS3 and starch intakes (but not conventional fiber (NSP)) in epidemiological observations demonstrate 25-50% relative risk reductions in colorectal neoplasms and cancer incidence.
- RS3 was better than RS2 or RS4 at relieving symptoms of constipation.
- RS3 shifts nitrogen excretion from urine to feces better than RS2, implying that RS3 is better for people with kidney or liver impairments than RS2 in mice.
- RS2 showed markedly better growth of Eubacterium rectale, a species associated with high butyrate production, when compared to RS4. Extraordinary increases bifidobacteria were associated with RS4 (10-fold in several human subjects).
Most of the hundreds of studies done over the past 30 years use RS2 from corn or potatoes as their source and see favorable results. RS3, when studied, was mostly in the form of retrograded corn or tapioca starch. Very few studies looked at the benefits of one RS source over another, or RS as found in real foods. We think it is prudent to include both RS3 and RS2 in your diet for the bulk of your RS needs, but don’t shy away from RS1 as intact seeds, legumes and whole gluten-free (GF) grains which have benefits of their own. A natural approach is probably best when it emulates your individual ancestral eating patterns…consume most of your starches fresh, cooked-cooled and some raw. Supplements can maintain or help meet health goals.
No Starch is an Island
Many things go into a healthy gut biome, and resistant starch is just one element of many. Certainly by now you realize that the gut microbiome plays a huge part in the breakdown and health benefits described here. Also, other fibers may be needed to assist resistant starch in its efforts to fuel your gut microbiome with fermentable fibers.
For instance, a fiber found in inulin-rich foods, fructoologosaccharide (FOS) acts synergystically with RS. The combination increases populations of beneficial microbes more than either alone. FOS ferments very fast while RS takes a bit longer to degrade through microbial actions, this factor makes a combination of these fibers more desirable than the fibers administered alone. Inulin acts much like RS3 as a slowly degraded fiber, and when combined with RS and FOS can create an accurate tool for targeted applications of prebiotics to certain areas of the colon. These factors can be exploited easily by the adventurous dieter by eating a well-balanced, fiber-filled meal paying attention to get all the different fermentable fibers together. In an experiment with 32 rats divided into 4 teams, the group fed a combination of RS and inulin for 21 days showed a greater diversity of gut flora, better colon health markers, and improved absorption of dietary calcium and magnesium.
But, But, Isn’t RS a dreaded FODMAP???
What, you don’t know what a FODMAP is?
FODMAP is an acronym for “Fermentable, Oligo-, Di, and Mono-saccharides, And Polyols.”
A diet for people with bowel disorders was developed that limits FODMAPs and is said to relieve symptoms for many, the trouble is, many of the FODMAPs are potent prebiotics and eliminating these compounds essentially starves the gut flora. While this may have short-term therapeutic benefits, it is not healthy in the long-run if gut health is your main concern.
Technically, RS is not a FODMAP, but the “F” kind of catches it as a fermentable substance. Really, it could have just as easily been called the “F” diet—not for the grade I give it, but for the avoidance of all things fermentable.
If you are following a strict no FODMAP diet, you’ll want to add RS to the list. You’ll also want to re-evaluate your reasons for avoiding all food for your gut bugs—it’s cruel and unusual punishment for trillions of hapless bystanders. While you may enjoy the relief afforded by FODMAP restriction it is at great cost to your gut flora. Seek and destroy the offending pathogens, and start eating prebiotics as soon as you can.
The Father of RS
Hans N. Englyst first coined the term “resistant starch” in 1982 while attempting to measure dietary fiber. He found that certain starch granules hindered his attempts to recreate digestion in a test tube and labeled the undigested portions of starch “resistant starch.” It seems at this point, RS was little more than a nuisance to researchers, but Englyst went on to publish dozens of papers discussing RS and ways to measure it.
At first, Englyst used ileostomy patients to measure RS. Ileostomy patients provide a perfect way to test for undigested starches because all of the food that leaves their small intestine is collected in a pouch and can be examined for anything that escaped digestion. Many of the RS content lists that were developed by Englyst using the ileostomy method are used to today as the “gold standard” to compared more modern methods of RS testing against.
How much RS is in this?
One reason you won’t be seeing RS listed on nutrition labels any time soon is because it’s so hard to measure. Take the potato for instance, the RS content changes drastically as the raw potato is cooked, cooled, and reheated numerous times. The variety of potato and cooking methods also impact the RS content. Except for the case of highly processed snack foods and bakery items, it’s better you simply learn which foods are rich in RS and how to best prepare them to maximize RS for your health.
Several different methods have been developed to measure the RS content in foods beyond a simple examination of ileostomy bags.
- The Berry Method was derived from Englyst’ experiments using pancreatic enzymes from pigs, but proved unreliable.
- The Champ method modified the Berry method to correct for pH and temperature and gave consistent RS measurements.
- Muir and O’Dea used a similar method, but the food was first chewed by human volunteers
- Bednar and associates developed a method in 2001 to measure RS using dogs with modified digestive systems and surgically implanted tubes to measure RS at different stages. This method was very accurate, but probably not very popular.
AOAC Method 2002.02 is now the standard method for measuring RS.
The Association of Official Agricultural Chemists adopted this method in 2002, and describe the method:
Starch is solubilized and hydrolyzed to glucose by the combined action of pancreatic-amylase and amyloglucosidase (AMG) for 16 h at 37°C. The reaction is terminated by addition of ethanol or industrial methylated spirits (IMS) and RS is recovered as a pellet by centrifugation. RS in the pellet is dissolved in 2M KOH by vigorously stirring in an ice–water bath. This solution is neutralized with acetate buffer and the starch is quantitatively hydrolyzed to glucose with AMG. Glucose is measured with glucose oxidase–peroxidase reagent (GOPOD), which is a measure of RS content. Nonresistant starch (solubilized starch) is determined by pooling the original supernatant and the washings and measuring the glucose content with GOPOD.
Even with this agreed-upon measuring standard in effect, differences are seen between testing labs and the terminology used makes it all very confusing for the average consumer.
Prior to adopting this standard, the AOAC sent identical samples of green banana, potato starch, corn starch, corn flakes, kidney beans, and several types of RS4 to 37 different labs for independent testing. The results were fairly consistent, but quite variable. For instance, the raw potato starch showed an average RS content of 63% on an “% as is” basis, with the ranges being between 56% and 76%.
To add to the complication, all of the labs present their data in three ways: “As-is basis,” “Dry-weight basis,” and “RS as a percentage of total starch.” When compared with these three terms, raw potato starch from 37 different labs is expressed like this:
RS Content of Raw Potato Starch, AOAC Method 2002.02
- As-is basis – 63%
- Dry-weight basis – 72%
- RS as a percentage of total starch – 73%
For reference, here are the RS contents of raw potato starch using the various other testing procedures: (all expressed as a percentage of total starch)
- Ileostomy patient studies—up to 83%.
- The Champ method—87.5%.
- Models that use human volunteers to pre-chew food—66%.
- Canine models of digestion—68%.
As you can see, pinning down the actual value of RS is not an extremely accurate science. With the AOAC testing standard in place, we at least have a common reference for all RS tests.
What can RS do for me?
Hundreds of studies have been conducted over the last 30 years on the effects of RS to:
- Improve bowel health
- Lowers pH
- Increases epitheleal thickness
- Kills cancer cells
- Lower postprandial glycemia
- Increase insulin sensitivity
- Reduce body weight and prevent weight regain
- Decrease inflammation in the intestines and entire body
- Reduce risk of breast cancer and colorectal cancer
- Reduce cholesterol/triglycerides
- Increase production of brain neurotransmitters serotonin and melatonin
- Remove certain pathogens from small intestine
- Preserve Vit D in the body
- Increase mineral and vitamin production and uptake
- Remove toxins and heavy metals from the bloodstream
- Increase satiety and regulate hunger hormones
- Reduce fat storage after meals
- Improve the gut microbiome (synergy, prebiotic, symbiotic)
- Protects probiotic bacteria
Looking closely at the list of studied benefits of RS, you can almost see a linear progression from its simple physical properties to its in-depth role in maintaining a healthy gut microbiome. This is also exactly how biological science has progressed during the same time as newer methods to test gut microbes come to light. Many of the older studies that yielded mixed results are being done again with a focus on how RS affects the microbiome and when looked at in that way, the studies prove successful, or shed light on why they failed.
Here are a few of the more common, well-studied, and much sought-after results of increasing RS in your diet:
Glucose Response and Insulin Sensitivity:
Probably the most widely studied effect of RS and one of its biggest “selling points” is in its control of blood sugar. From a well-documented “second-meal effect” to complete reversal of Type 2 Diabetes, RS could be a godsend for many and is being studied extensively for ways to bring it to the masses. Studies looking at different types of RS, found that they are equally effective at controlling postprandial blood glucose spikes and that RS exerts a stability in blood glucose levels.
Other notable studies have shown increases in “whole body insulin sensitivity,” the holy-grail for weightlifters and body-builders who often go to great lengths to achieve this effect, and since insulin resistance is closely associated with complications of diabetes and heart disease this remains at the forefront of RS research. The blood sugar changes that are seen when RS is incorporated into the diet can be compared to the blood sugar changes seen when diabetics undergo gastric bypass surgery, an almost immediate increase in insulin sensitivity results and is closely associated with changes to the microbiome of intestinal bacteria.
Body Weight Regulation:
As a diet aid, RS will fall short. It’s not as simple as taking a diet pill and the studies in this area have shown mixed results, but what is very apparent in the studies of RS and weight is that a when gut bugs are fed RS, they will do everything in their power to help get you to a lean, healthy state. Studies that look simply at weight often fail to see reductions because RS can actually lead to a heavier, thicker, healthier intestinal tract and increase the numbers of bacteria living there—a weight gain everyone should be happy with. Another interesting field of research into RS has to do with re-gaining weight lost through exercise; it was found that after losing a considerable bit of fat, keeping it off was easier with RS than with continued exercise—and certainly intestinal microbe driven through better hunger signals and fat storage hormones. What is really exciting is that the addition of RS, post weight loss, clearly showed a trend toward muscle growth and away from fat storage—the main goals for improving insulin sensitivity.
You may have heard of “cortisol,” a stress hormone that often stymies weight loss and muscle building progress, well, cortisol is no match for RS…cortisol is lowered on an RS supplemented diet and helps explain the reduction in weight regain and also has been implicated in whole-body energy metabolism. The cortisol connection is entirely driven by gut bugs and possibly one of their most important contributions to our overall health.
There are very few studies looking at the antiinflammatory effects of RS, but almost every study on gut microbes addresses the fact that gut bugs play a huge role in lowering inflammation. The studies in which inflammation were addressed showed conclusively that the addition of RS to the diet decreased inflammation in the intestines and body-wide. This area will undoubtedly be explored further as new evidence on the connection between gut bugs and inflammation come to light. Inflammation is characteristic of heart disease, diabetes, obesity, and many other diseases. RS is one of the keys to unlocking the mystery behind inflammation.
Cholesterol and Triglycerides:
Chronic RS intake reduces levels of ldl (bad) cholesterol and triglycerides. That’s really all you need to know, but in case you love facts, RS also lowers fasting serum triglycerides and cholesterol levels and RS lowers levels of liver triglycerides and cholesterol as well as triglycerides found in adipose (fat) tissue. Furthermore, genes in the liver which control cholesterol production were lower and genes which clear cholesterol were higher after continued feedings of RS.
Early investigations into RS focused on positive changes to the colonic environment such as lowered pH and elevated production of butyrate. Both of these changes decrease levels of pathogenic intestinal microbes and improve bowel functions. As more research is done on the positive effects of a well-fed gut microbiome, the importance of RS has been elevated to epic proportions. Many of the old studies from the 80’s and 90’s are being re-created with a focus on gut bugs and through test methods for gut microbes that didn’t exist back then, the studies are proving very insightful.
In numerous early studies, researchers were confused as to why the results of RS experiments varied widely between study participants. Modern studies looking at microbes eating RS have discovered that certain key microbes must be in place before RS can be fully utilized. For instance, when a gut microbe known as Ruminococcus bromii is thriving, RS causes massive increases in beneficial gut microbes Bifidobacterium and Bacillus species. When Ruminococcus bromii is absent, no change in Bifidobacterium or Bacillus is detected. This discovery led to new theories on the fermentation of RS by gut bacteria, one theory, known as the “Keystone Species Theory” describes that RS is not fermented simply by many different microbes, but selectively targeted by only a few “Keystone” species and the byproducts are then consumed by RS co-feeders in a remarkable progression of events which leads to the production of important chemicals and compounds important to intestinal health.
Nearly all of the studies done on RS in the last 3 years have been centered around cancer prevention and cures—and not just colorectal cancer, but also breast cancer and the use of RS as a chemotherapy enhancer. 20
RS has been shown to reduce the survival of human colon cancer cells through its stimulation of short-chain fatty acids. When cancer cells are exposed to high doses of RS boosted butyrate, they are killed through DNA fragmentation, also known as cell apoptosis. A diet high in RS has been shown to prevent the formation of cancer cells altogether.
A few years back, lots of press was given to the reports that red meat consumption causes cancer. What wasn’t widely disseminated were the studies that showed when RS was fed alongside red meat, the cancers never formed and the damaging effects of meat were totally negated and that the intestinal cells that are at risk for meat-induced damage were made much healthier with the inclusion of RS.
Researchers often inject animals with powerful carcinogens and assess their health after testing anti-cancer protocols. One such study looked at the effects of raw starches (RS2) and man-made starches (RS4) comparing their anti-cancer properties. In a head-to-head comparison, the raw starches beat the man-made starches in fermentation and anti-cancer properties. However, in another study, both RS2 and RS4 were equally effective at providing cancer protection.
Due to it’s “resistant” nature, RS is being used in chemotherapy to protect cancer drugs from digestive processes and to target colon cancer cells. When drugs are coated with an RS layer of a particular thickness, a very precision targeting method is produced with profound impact on the treatment of bowel cancer.
And lastly, breast cancer is seeing the benefits of RS therapy. Breast cancer is a huge concern for women on estrogen therapy—recent mouse studies have shown a decrease in breast cancer cells and improvements to how their bodies metabolized circulating estrogen.
Preserves Vitamin D:
Another very recent discovery is that when eating a diet high in RS, symptoms of vitamin D deficiency are ameliorated. This is especially important for Type 1 and Type 2 Diabetics with impaired kidneys who excrete excess vitamin D in their urine. Diabetes is becoming an epidemic and RS has been shown to mitigate the effects of diabetes, and may eventually prove to be the cure.
An interesting advancement in RS technology has been its synergistic effects when combined with live probiotic bacteria prior to consumption. RS displays an amazing ability to “capture” nearby microbes through a process known as ligand mimicry. This same process that is used to treat cholera patients is also used to package probiotic microbes in the supplement industry.
Through a modern invention known as “microencapsulation,” tiny beads of RS are coated with beneficial bacterial strains and they, in turn, are coated with more RS. This provides protection and food for the live organisms to survive lengthy storage times on the shelf and also provides protection from harsh stomach acid and digestive enzymes which normally destroy live bacteria destined for the large intestine. Early attempts at this synergistic feature of RS and probiotics were undertaken using ice cream with a high RS content to capitalize on the effects of low temperature on the survival of probiotic strains of microbes, however, these methods have been replaced in favor of microencapsulation, although the ice cream method has returned recently and a 2013 study showed it may prove highly stable.
For the adventurous home-enthusiast of RS consumption, the property of RS to preserve microbes can be used to increase the effectiveness of your expensive probiotic supplements. Simply mix your supplements with a cold liquid containing a spoonful of a raw starch such as potato, plantain, or tapioca starch, stir and drink. Probiotic pills in capsule form can be emptied into the mixture for good effect. If you are a consumer of yogurt, kefir, kombucha, or kvass, adding a spoonful of RS to the mix will increase the likelihood of the bacteria present in these getting to, and making a home in, your large intestine.
How much do we eat? What about everyone else?
As worldwide cancer and disease rates climb, researchers have been examining the diets of different populations. One thing modern civilizations have in common is their distinct lack of RS. In 2004, the AOAC conducted a survey and found the worldwide consumption of RS was 7 grams per day, with the United States and western European countries on the lower end and less developed countries at the higher end.
- Sweden – 3.2g
- United States – 4.9g
- Australia – 5.3g
- Italy- 8.5g
- China – 14.9g
Stale Maize Porridge
There are so many factors in play here that there can be no simple correlations, however, a really great study was done in 2007 to compare the relatively high rates of colorectal cancer among African Americans and the very low rates found in Native Africans living a simple, rural life.
In this study, the diets and lifestyles of 17 African American and 18 Native Africans were examined. The colorectal cancer rates between these groups was less than 1 in 10,000 for the Native Africans and 65 in 10,000 for the African Americans. During the intense scrutiny, several glaring disparities were evident…the Native Africans were consuming much more resistant starch. A staple in the Native African diet was cornmeal porridge which was their main source of carbohydrates, and approximately 20% resistant starch. Their intake was close to 50 grams per day of RS compared to the African American intake of less than 5 grams per day.
An examination of the rural African diet showed that it was relatively lacking in dietary fiber, but very high in RS which ensures their colons remain very resilient to cancer formation. Interestingly, it’s not only the choice of food (maize porridge) but the traditional preparation method that makes it so high in RS. Typically the maize porridge is made by heating cornmeal in boiling water. The finished product is then stored for days and consumed cold—this leads to the formation of retrograded RS3 and when consumed is fermented into the short-chain fatty acids such as butyrate and propionate leading to increased numbers of beneficial gut bacteria and healthier colons almost completely lacking in signs of inflammation and cancer.
Furthermore, these same groups of stale maize porridge eaters were studied in 1986 where it was determined that the simple, high fiber diet significantly lowered fecal pH, and indicator of gut health, and protected the connoisseur of such tasty fare from colorectal cancer.
The Australian Paradox
Earlier we said, “don’t confuse resistant starch with dietary fiber.” The Australian Paradox illustrates our point. Nearly 30 years ago, Australia was faced with a crisis—they had one of the highest rates of colorectal (bowel) cancer among all ‘civilized’ nations. When they examined what the average Australian was eating, it was clear that they lacked dietary fiber. The Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO), the Australian federal government agency for scientific research, began a systematic approach to increasing the fiber intakes of Australians. Through research, advertising, and training Australians now eat more fiber per capita than any other Western nation…and they also still have the highest rate of bowel cancer. Clearly something is wrong! This seeming mismatch has been termed, “The Australian Paradox.” A high fiber diet should lead to reduced risk of colorectal cancer, not increased.
Rural Native Africans eating a very basic diet high in resistant starch and low in dietary fiber have a colorectal cancer rate of less than 1 in 10,000. Australians eating a diet low in RS and high in dietary fiber have a colorectal cancer rate of 1 in 12.
As you can imagine, CSIRO is shifting their focus from dietary fiber to resistant starch. They have issued a recommendation of 20 grams of RS per day, the first such recommendation in the world, and have begun numerous partnerships with food producers to increase RS in the food supply. While RS may not be the ultimate solution to the Australian Paradox, emulating a diet where colorectal cancer is nearly unheard of is a good start.
The Butyrate Paradox
Another paradox exists in the study of colorectal cancer called the “Butyrate Paradox.”
Butyrate is formed by intestinal microbes from highly-fermentable fiber residues, such as those from resistant starch, oat bran, pectin, and guar. Resistant starch consistently produces more butyrate than other types of dietary fiber but is largely missing from most diets, as are the other main butyrate producers. The role of butyrate in normal cells is completely different from its role in cancer cells—the butyrate paradox.
In normal colon cells, butyrate has an anti-inflammatory, health promoting effect, but just the opposite effect on cancer cells—butyrate causes cancer cells to self-destruct and die. Little is known about the signaling circuits that cause cancer cells to undergo apoptosis when exposed to butyrate, but a recent hypothesis has been proposed:
In a normal, healthy large intestine, butyrate is a preferred energy source. However, in the shortage of butyrate, attributed partly by “Western diet”, glucose is substituted as the energy source for survival of these colonocytes. As they evolve to adapt to the new conditions, genetic manipulations are initiated with subsequent loss of function of critical genes and eventual loss of ability to undergo programmed cell death. These cells may therefore be considered as “normal” so that if the initial or healthy environment has been re-introduced, for example, by the presence of higher concentrations of butyrate, they will not be able to adapt rapidly due to their altered genetic make-up. Hence, they will undergo butyrate-induced apoptosis, as seen in many in vitro and animal studies.
In short, the answer to the butyrate paradox is to eat more resistant starch and other dietary fibers that produce butyrate. Without a steady supply of butyrate, colon cells turn to other fuels and don’t behave normally. They lose their ability to self-destruct and turn cancerous. Normal cells self-destruct on a regular basis and when they are damaged, this keeps the colon health and cancer-free. A colon devoid of butyrate will soon become ill. A colon flooded with resistant starch will be happy and provide many years of trouble-free service.
The Carbohydrate Gap
Another major discrepancy in nutritional health science is found in our requirement for butyrate versus what the normal diet provides. Long-standing recommendations for 20-30 grams of fiber per day might be enough to produce all the butyrate we need if it all came from highly fermentable, butyrate producing fiber types, but sadly it doesn’t. The fiber in most people’s diet is comprised of cellulose and plant cell walls, known as non-starch polysaccharides (NSP), and these produce very little butyrate. Oligosaccharides (OS), such as inulin and pectin, produce more butyrate than NSP, but are not found in large quantities in nature.
It’s been calculated that we’d need to consume over 80 grams of fiber per day to meet our requirements for butyrate, and this is only if all of the fiber were highly fermentable. As discussed previously in the book, some of our ancestors appeared to have eaten over 130 grams of fermentable, OS-type fiber daily—a feat that would be hard to match today. The 15-20 grams of dietary fiber that most people consume daily doesn’t even account for 25% of the butyrate producing fiber we need, however, adding in 20-40 grams of resistant starch would bridge this gap nicely.
Throughout the history of mankind, we enjoyed resistant starch. Whether by accident, luck or design, it’s undeniable that RS is a big part of our past.
After we marched out of Africa, the first areas we settled were filled with palms. Palmae is one of the oldest plant families on earth and many early societies developed entire lifestyles in synergy with the various palm species:
- Date palm (Phoenix dactylifers) – Arabs of the sub-Saharan
- Palmyra palm (Borassus flabellifer) – Inhabitants of South India
- Lontar palm (Borassus sundaicus) – Roto islanders of Indonesia
- Coconut palm (Cocos nucifera) – Indo-Pacific Islanders
- Oil palm (Elaeis quineens) – West Africans
- Sago palm (Metroxylon sagu Rottboll) – Malaysians
- Moriche palm (Mauritia flexuosa) – American Paleo-Indians
What all of these palms had in common were amazing sources of fiber, particularly resistant starch. For instance, the Sago palm was the main source of subsistence throughout southern Asia until rice was introduced in 2500 BC. The sago palm is an amazing RS factory. The first part of its life it looks like a short, trunkless palm tree, but when it is about 10 years old, it will send up a trunk 20-30 feet tall after which it flowers and dies. The year before it flowers, the large trunk is filled with up to 2000 pounds of easily extracted starch. The starch is unique in that it was easily isolated and dried, and when cooked and cooled, retrogrades into one of the most stable RS3 sources on the planet. Products made from sago starch can be stored for exceptionally long periods and helped the seafaring Malaysians travel far and wide throughout the Malay Archipelago. To this day, 25-40,000 tons of sago products are exported annually from Malaysia to the rest of the world.
One of the best sources of RS2 comes from the mountainsides of Asia.
Dioscorea opposita, also known as Nagaimo, Japanese Mountain yam, Chinese yam, and Korean yam. It is often used in the Japanese noodle dish tororo udon/soba and as a binding agent in the batter of okonomiyaki. The grated nagaimo is known as tororo (in Japanese). In tororo udon/soba, the tororo is mixed with other ingredients that typically include tsuyu broth (dashi), wasabi, and green onions. Also eaten in China, Japan, Vietnam, Korea and the Philippines.
Raw Chinese yam (Dioscorea opposita) is an excellent source of RS, as studied here:
We examined the effects of raw Chinese yam (Dioscorea opposita), containing resistant starch (RS), on lipid metabolism and cecal fermentation in rats. Raw yam (RY) and boiled yam (BY) contained 33.9% and 6.9% RS, respectively…These results suggest raw yam is effective as a source of RS and facilitates production of short chain fatty acid (SCFA), especially butyrate.
Our past is filled with ample consumption of RS2, raw starch granules:
There were also societies that utilized isolated, raw starches (RS2) in a variety of interesting ways, but never as a main source of calories and nourishment.
- Horchata de Chufa, a tiger nut starch drink that is still enjoyed by many around the world even today;
- Fufu, a starchy dough made from cassava root eaten in Africa;
- Chicha, similar to Horchata de Chufa but made with corn
- Chuno, a dehydrated potato staple of the Andes
- Tororo, made of the Asian yam Dioscorea opposita, often eaten with Natto
- Nuts and Seeds, probably every single culture in the history of mankind has enjoyed munching on raw nuts and seeds. Sunflower seeds, pumpkin seeds, chia, flax, and all manner of tree and ground nuts are universally enjoyed by people around the world and contribute to a healthy gut
Additionally, much evidence of RS3 consumption abounds:
- Yam cakes
- Dried, cooked tubers (ie. potato chips)
It may be the “leftovers” that have given us our biggest supply of RS3 over the years. People living in so-called “Blue Zones” known for tremendous longevity are known to subsist on meager rations of leftover pasta and legumes.
While there has been no official policy in the US or any other country, Australian officials are recommending a minimum of 20 grams of RS daily. Many of the studies we looked at used a range of 20-50 grams per day of RS to achieve the colon health and other aspects attributed to RS. No upper limit has been defined except in the case of excess gas or bloating noted by some study participants, but any excess starch consumed will simply pass through the entire digestive system undigested and harmlessly be eliminated.
In the absence of any official guidelines, I’d like to offer these:
Eat daily from a selection of beans, rice, potatoes, bananas, plantains, sweet potatoes, squash, and other plants, roots, and tubers known to be rich in RS and inulin.
Prepare your starchy foods in a way that will maximize the RS value, ie. cooking and cooling, raw or dried.
For a supplement, use 1-2TBS of potato starch, Hi-Maize corn starch, or banana flour. There are even supplements availble that contain RS and other fibers, like Gut Garden’s Blend. Add it to a smoothie or just mix in water/yogurt. Most people find that 1-2TBS seems to be the sweet spot, but don’t be afraid to try more or less. Many people like 4TBS a day, others 1 teaspoon.
Calorie counters rejoice!
When counting either total calories or carbohydrate calories, resistant starch is treated a bit differently. RS is not absorbed in the small intestine, therefore providing no direct energy (calories) to fuel your body. It is, however, converted into short-chain fatty acids in the large intestine. These fatty acids are either absorbed into the bloodstream or used by cells that line the colon as energy to fuel their activities.
Every 1 gram of RS is thought to provide approximately 1.5 calories (kcal) to the human body in terms of energy. Therefore, a daily intake of 40g RS would account for only 60 calories and should be counted as “fat” calories, not “carbs.”