A few years back, I briefly covered a throwaway Yahoo! article  about how “carbs will make you lose weight” because so many readers had emailed about it. It turned out that the “carbs” in the article were resistant starch, a type of carbohydrate that our digestive enzymes cannot break down. I’ll admit now, with regret, that I didn’t look as deeply into the matter as I might have. I didn’t dismiss resistant starch, but I did downplay its importance, characterizing it as “just another type of prebiotic” – important but not necessary so long as you were eating other fermentable fibers. While technically true, we’re fast learning that resistant starch may be a special type of prebiotic with a special place in the human diet.
Before I go any further, though, a series of hat tips to Richard Nikoley , Tatertot Tim, and Dr. BG , whose early and ongoing research into the benefits, real-world implications, and clinical applications of resistant starch have proved to be a real asset for the ancestral health community. Oh, and I even hear tell that they’re writing a book on the subject. Interesting…
What Is Resistant Starch?
When you think about “starch,” what comes to mind?
Glucose. Carbs. Elevated blood sugar. Insulin  spikes. Glycogen  repletion. Basically, we think about starch that we (meaning our host cells) can digest, absorb, and metabolize as glucose (for better or worse).
Officially , resistant starch is “the sum of starch and products of starch degradation not absorbed in the small intestine of healthy individuals.” Instead of being cleaved in twain by our enzymes and absorbed as glucose, resistant starch (RS) travels unscathed through the small intestine into the colon, where colonic gut flora metabolize it into short chain fatty acids. Thus, it’s resistant to digestion by the host.
There are four types of resistant starch:
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.”
It’s almost certain that different RS types have somewhat different effects on our gut flora , but the specifics have yet to be fully elucidated. In general, RS (of any type) acts fairly similarly across the various types.
Where Do We Get It?
We can get RS from food. The richest food sources are raw potatoes , green bananas, plantains, cooked-and-cooled potatoes, cooked-and-cooled-rice , parboiled rice, and cooked-and-cooled legumes.
We can get RS from supplementary isolated starch sources. The best sources are raw potato starch, plantain flour, green banana flour, and cassava/tapioca starch. Raw (not sprouted) mung beans are a good source of RS, so mung bean starch (commonly available in Asian grocers) will probably work, too.
The most reliable way to get lots of RS, fast, is with raw potato starch. There are about 8 grams of RS in a tablespoon of the most popular brand: Bob’s Red Mill Unmodified Potato Starch . It’s also available at Whole Foods.
For an exhaustive compendium of RS sources, check out this PDF  from Free the Animal.
What Does It Do for Us?
Like any other organism, gut bacteria  require sustenance. They need to eat, and certain food sources are better than others. In essence, RS is top-shelf food for your gut bugs. That’s the basic – and most important – function of RS.
What Are the Health Benefits of Consuming RS?
What does the research say?
Preferentially feeds “good” bacteria responsible for butyrate production. It even promotes greater butyrate production than other prebiotics . Since the resident gut flora produce the butyrate, and everyone has different levels of the different flora, the degree of butyrate production varies according to the individual, but resistant starch consistently results in lots of butyrate  across nearly every subject who consumes it. Butyrate is crucial because it’s the prime energy source of our colonic cells (almost as if they’re designed for steady exposure to butyrate!), and it may be responsible for most of the other RS-related benefits.
Improves the integrity and function of the gut. Resistant starch basically increases colonic hypertrophy , making it more robust and improving its functionality. It also inhibits endotoxin from getting into circulation  and reduces leaky gut , which could have positive ramifications on allergies and autoimmune conditions.
Lowers the blood glucose response to food. One reason some people avoid even minimal amounts of carbohydrate is the blood glucose response; theirs is too high. Resistant starch lowers the postprandial blood glucose spike . This reduction may also extend to subsequent meals .
Reduces fasting blood sugar. This is one of the most commonly mentioned benefits of RS, and the research seems to back it up .
Increases satiety. In a recent human study , a large dose of resistant starch increased satiety and decreased subsequent food intake.
May preferentially bind to and expel “bad” bacteria. This is only preliminary, but there’s evidence that resistant starch may actually treat small intestinal bacterial overgrowth by “flushing” the pathogenic bacteria  out in the feces. It’s also been found to be an effective treatment  for cholera when added to the rehydration formula given to patients; the cholera bacteria attach themselves to the RS granules almost immediately for expulsion.
Enhances magnesium absorption. Probably because it improves gut function and integrity, resistant starch increases dietary magnesium absorption .
What do user anecdotes say?
Improves body composition. I’ve heard reports of lowered body fat and increased lean mass after supplementing with or increasing dietary intake of RS. Seeing as how RS consumption promotes increased fat oxidation  after meals, this appears to be possible or even likely.
Improves thyroid function. Many RS supplementers have noted increases in body temperature, a rough indicator of thyroid function.
Improves sleep, conferring the ability to hold and direct (in real time) private viewings of vivid movie-esque dreams throughout the night. I’ve noticed this too and suspect it has something to do with increased GABA (gamma-aminobutyric acid) from the increased butyrate. Another possibility is that resistant starch is feeding serotonin-producing gut bacteria, and the serotonin is being converted to melatonin when darkness falls.
Increases mental calm. Many people report feeling very “zen” after increasing RS intake, with reductions in anxiety and perceived stress. The latest science indicates that our gut flora can impact our brain , and specific probiotics are being explored as anti-anxiety agents , so these reports may very well have some merit.
Are There Any Downsides?
For all the success stories, the message boards are also rife with negative reactions to RS. They take it, maybe too much to start, and get gas, bloating, cramping, diarrhea or constipation, a sense of “blockage,” headaches, and even heartburn. I think RS supplementation may be a good measuring stick for the health of your gut. Folks with good gut function tend to respond positively, while people with compromised guts respond poorly. The gas, bloating, cramps and everything else are indicators that your gut needs work. But it’s not the “fault” of resistant starch, per se.
What to do if you’re one of the unlucky ones? You’ve got a few options:
You could skip it altogether. I think this is unwise, personally, because the role of fermentable fibers , including RS, in the evolution of the human gut biome/immune system has been monumental and frankly irreplaceable. There’s a lot of potential there and we’d be remiss to ignore it.
You could incorporate probiotics. You need the guys that eat the RS to get the benefits of consuming RS. And sure, you have gut flora  – we all do, for the most part, except after colonic sterilization before a colonoscopy or a massive round of antibiotics, maybe – but you don’t have the right kinds. Probiotics, especially the soil-based ones (the kind we’d be exposed to if we worked outside, got our hands dirty, and generally lived a human existence closer to that of our ancient ancestors), really seem to mesh well with resistant starch.
You should reduce the dose. Some people can jump in with a full 20-30 grams of RS and have no issues. Others need to ramp things up more gradually. Start with a teaspoon of your refined RS source, or even half a teaspoon, and get acclimated to that before you increase the dose.
You could eat your RS in food form. Potato starch and other supplementary forms of RS are great because they’re easy and reliable, but it’s also a fairly novel way to consume RS. You might be better off eating half a green banana instead of a tablespoon of potato starch.
The first time I tried potato starch, I got a lot of gas. Not the end of the world, and I realize gas is a natural product of fermentation, just unpleasant. It died down after a few days, but it was only after I added in some of my Primal Flora  probiotic that I started seeing the oft-cited benefits: better sleep, vivid dreams, a more “even keel.”
Now, I do potato starch intermittently. I’m very suspicious of eating anything on a daily basis. I tend to cycle foods, supplements, exercises, everything. Gas production goes up every time I re-start the potato starch, but not unpleasantly so and it subsides relatively quickly, especially when I take the probiotics .
So there’s a learning curve to RS. It’s not a cure all, but neither is anything else. It’s merely an important, arguably necessary piece of a very large, very complex puzzle.
Resistant starch is vitally important for gut (and thus overall) health, but it’s not the only thing we need. It’s likely that other forms of fermentable fiber (prebiotics ) act synergistically with RS.
Hey, it’s almost like eating actual food with its broad and varied range of bioactive compounds, polyphenols, fibers, resistant starches, vitamins, and minerals tends to have the best effects on our gut biome! You can certainly enhance the picture with isolated refined resistant starches and fibers  like unmodified potato starch, but they can’t replace what our bodies really expect: the food.
Let me know what you think, and I hope you find this guide useful.
What’s your experience been with resistant starch? Good, bad, neutral? Let’s hear all about it!
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