PlantainsStarch, forbidden blood sugar spiker for some, “Perfect Health” food for others, but what if there was more to starch than meets the eye, or should I say gut? Resistant starch (“RS”) is currently a hot topic in the Ancestral Health community because of its impact on gut bacteria and the potential benefits this may confer. Supporters cite deeper sleep, decreased body fat, and a host of other benefits, but is RS all good or should we exercise some healthy skepticism?

Starch 101 – The Basics

Starch is how green plants store energy. This energy is formed by way of the interaction between sunlight and specialized plant cell structures called chloroplasts. During this process, generally known as photosynthesis, chloroplasts combine water and carbon to form glucose.

In some circumstances, however—lets say a particularly sunny day—excess glucose may be formed. This is where starch comes in. By stringing together individual molecules of glucose, plants form tightly bound granules of starch that can be tucked away in roots, shoots, or other parts of the plant. On a cloudy day, when sunlight is scarce, plants can then break down their stored starch for energy.

Varieties of Starch

Plants don’t store all of their starch in the same way, however, and for this reason, whole food sources of starch—such as a green plantain, a grain of rice, or a potato—contain a variety of starches. The first of these varieties, and typically the most abundant, is amylopectin. The amylopectin molecule has many branches that you could visualize as similar to the arms of a tree. Tree branches serve the purpose of creating more surface area, and the branching arms of amylopectin do the same thing. All that surface area exposes the molecule to digestive enzymes which, in both plants and humans, allows amylopectin to easily be converted back to sugar.

The second primary form of starch, amylose, lacks the branches possessed by its sister molecule amylopectin. You could imagine amylose as something more akin to a bare tree trunk. Tree trunks are solid and strong, as is amylose. The tight structure of this molecule presents less surface area for digestive enzymes to attach to and because of this, it’s said that amylose resists digestion. As you might imagine, this is why amylose is referred to as resistant starch (RS).

Amylose isn’t the only type of resistant starch however. For a variety of reasons, even digestible starch can be referred to as resistant, so to keep everything straight, the following categories are used:

RS Type 1 – Starch bound by indigestible plant cell walls; found in beans, grains, and seeds.

RS Type 2 – Starch that is intrinsically indigestible in the raw state due to its high amylose content; found in potatoes, bananas, plantains, Type 2 RS becomes accessible upon heating.

RS Type 3 – Retrograded starch; when some starches have been cooked, cooling them (fridge or freezer) changes the structure and makes it more resistant to digestion; found in cooked and cooled potatoes, grains, and beans.

RS Type 4 – Industrial resistant starch; type 4 RS doesn’t occur naturally and has been chemically modified; commonly found in “hi-maize resistant starch.”

(Category list from, “The Definitive Guide to Resistant Starch)

RS and Blood Sugar

Because of it’s unique properties, RS doesn’t behave the same way regular digestible starch does. When you eat digestible starch, the molecules are quickly broken down by enzymes in your saliva and gut, converted to glucose, and absorbed by the small intestine. In some cases, this process can occur so fast that the resultant blood sugar spike from eating starch is higher than if you ate pure sugar!1

Consuming RS, on the other hand, not only keeps blood sugar levels on an even keel, it may even improve insulin sensitivity in some individuals.2  This is certainly a quality that suggests RS is an interesting subject for personal experimentation—especially for those who have long shunned starch, fearing an out-of-bounds blood glucose spike.

Bacteria and Butyrate

Stable blood sugar levels aren’t the only attractive properties of RS. While our human digestive tract lacks the ability to fully break down resistant starches, these molecules create a feeding frenzy for the billions of bacteria living in our guts. The gut microbiome is complex and the introduction of RS sets off a chain reaction with different species of bacteria playing different roles. One or more types of bacteria may feed directly off of RS, while others take advantage of the waste products created by their bacterial brethren. It’s thought that some of the beneficial effects attributed to RS are actually the result of these bacterial waste products. One “waste” product that is particularly useful to our body is the short chain fatty acid butyrate.

Butyrate is found in other foods however, with butter being the richest natural source, so is RS necessary? According to Dr. Grace Liu, Richard Nikoley, and Tim Steele—a trio separated by geography but united in their passion for unlocking the possibilities of superior gut health—it most certainly is. They offered to tackle this question, and a few others, in the following three sections.

Part 1: Butter Cannot Match Microbial-Made Butyrate in Our Guts

There are no studies to be found on the effects of dietary butyrate as a means to fuel colonocytes (the cells of the large intestine).  All dietary butyrate, including that derived from ingested butter, is treated as normal fat in the stomach and small intestine, and absorbed into circulation by the time it reaches the large intestine. Dietary butyrate cannot provide energy to the colonocytes which require ample butyrate to fuel their performance.

In butter, butyrate is approximately 4% by weight. One would need to consume 170g (2/3 cup) of butter to obtain the identical amount of butyrate that’s fermented daily by the average person’s gut microbiota. This also assumes that all that dietary butyrate somehow managed to actually arrive at the large intestine intact, bypassing the digestive processes of the small intestine in the process.

There have been a few studies with butyrate supplied in pills to treat Crohn’s disease and butyrate enemas; both share mixed results.3 4 5 The best place to get butyrate is from your own butyrate factories— your gut bugs.  Many different fiber types result in butyrate production, but resistant starch clearly comes out on top in study after study. Interestingly, the production of butyrate is only one of RS’ tricks.

Part 2: Beyond Butyrate

As a prebiotic, RS stimulates the growth of bifidobacteria and other major butyrate producers.6 Bifidobacteria is a microbial species that is considered an “A-List” gut bug, associated with improvement of various conditions, as well as production of B and K vitamins.7 8

RS is a fiber and prebiotic, plain and simple. Our ancestors never worried about eating enough fiber or prebiotics, just as they didn’t worry about vitamin D from sunlight or getting enough probiotics. Their perfect probiotic was called dirt, which coated nearly every morsel that touched their lips and every item they owned or shared.

One of the earliest prebiotics that fed us and our morphological evolution was RS.  It was found in soft and palatable RS-enriched underground storage organs that grew all over the African landscape where we evolved.  It’s no great secret that our ancestors ate large amounts of yams, seeds, nuts, roots, and sedge tubers. In turn, their guts were full of beneficial butyrate-pumping strains of microbes which were fueled at every meal and snack.

RS is a great source of food for our gut microbes.10 11 When we eat RS-deficient paleo diets, refined foods, or low starch diets that are completely digested in our small intestines, there’s nothing left for the trillions of hungry symbiotic inhabitants in our large intestine.They will eat—they are survivors after all—or go extinct. The populations of beneficial microbes can be quickly taken over and crowded out by the mongrels that are only out for themselves.  Many changes can ensue: pH rises, muscles weaken, immunity suffers, permeability surges and allows toxins, microbes and undigested food to breach the gut into the bloodstream.12

Part 3: Recommendations for RS supplementation:

  • Attempt to eat 20-40 grams of resistant starch daily; start low, go slow.
  • Eat from a selection of cooked and cooled beans, rice, and potatoes; green, unripe bananas and plantains (good in smoothies, or dehydrated and used as a dipping substrate—such as for hummus, another RS rich food); sweet potatoes, squash, and other plants; nuts, roots, tubers, and soaked non-gluten grains known to be rich in many kinds of fiber including RS; oligosaccharides, and others.
  • Maximize the RS value of starchy foods by cooking them and then allowing them to cool (re-heating is OK) or eat them raw or dried.
  • Use a prebiotic supplement to make up the difference:  Potato starch, green plantain or green banana flour, for instance.
  • Diversify fruits and vegetable, and don’t rely exclusively on an extracted source of RS for the bulk of your prebiotic needs.

RS Cautions and Concerns

The benefits of RS seem to be undeniable. However, all guts are not created equal and some individuals may not respond favorably to increased RS intake. According to Norm Robillard Ph.D., microbiologist and author of the “Fast Tract Digestion” book series, if you suffer from small intestinal bacterial overgrowth (SIBO), irritable bowel syndrome (IBS), acid reflux, or have an autoimmune condition such as rheumatoid arthritis or ankylosing spondylitis, large amounts of RS may worsen symptoms.

“IBS is linked to an increase in Firmicutes type bacteria over Bacteroidetes bacteria but an overall decrease in microbiota diversity,” Robillard states. He explains that a healthy gut is like a rainforest, with a variety of bacterial species all competing with each other in an environment that presents a broad spectrum of possible food sources. An unhealthy gut, by comparison, is much less diverse where certain types of bacteria dominate. In the latter scenario, if one group of bacteria like Firmicutes, which is able to effectively utilize RS as food, is out of proportion, adding RS to ones diet can cause the bacterial population to surge, and along with it, increase symptoms such as intestinal gas.

“The diet that continues to make the most sense for people with SIBO in my view, is one that quantitatively limits, not eliminates, fermentable carbs,” Robillard suggests, “This effectively puts the polysaccharide loving microbes on a diet.” He recommends limiting fermentable carbohydrate, including resistant starch, intake to 45 grams per day and to eat them in combination with animal-based foods. According to Robillard, this will promote bacterial species that metabolize amino acids and other animal-based macronutrients as well as a moderate level of Firmicutes that prefer complex carbs. The results will be greater diversity in gut bacteria, fewer symptoms and overall improvement in SIBO-related illnesses.

Final Thoughts

Our understanding of the complex relationship between our human bodies and the trillions of microbes that live on and in it is still in it’s infancy. After it was realized in the later part of the 19th century that bacteria and other microorganisms were the cause of many diseases we sought to eliminate them with antibiotics, obsessive sterilization routines, and hand sanitizers. This “war on bacteria” has undoubtedly saved millions of lives, but we are now entering an era where the negative consequences of this war are being realized.

The needle is swinging and we are now learning to embrace and even encourage our resident bacterial populations. RS may represent part of this healing process, a way for us to feed what we have long fought, but unfettered optimism still needs to be tempered with an undeniable reality; our bodies are not pristine and our homes are are a long way from the ancestral savannah. The path of self exploration and self study is a noble one, but if history is to be our guide, we would do well to tread carefully when tinkering with nature, even when it is our own.


For more information about RS (and the gut microbiome in general), be sure to visit the following links

  • “A Resistant Starch Primer for Newbies” on Richard Nikoley’s “Free the Animal” blog

 RS Recipes



1. “Glycemic index and glycemic load for 100+ foods

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