RS2 and RS3 are Not Exactly the Same Thing(Hat tip: M. McEwen) Feeding raw potato (RS2) in this ancestral diet study (human v. Theropithecus
gelada) appeared to overfeed and increase the RS2-chomping gut populations—Bacteroides and E. rectale—in the human simulated gut. Populations that do not eat RS2 at all or proficiently—lactobacilli and bifidobacteria—were decreased with raw potato. These sub-colonies prefer dining on oligosaccharides (beans, inulin, endive, banana), RS3 and other fiber.
However, with simulated gelada baboon gut, minimal changes were observed and this is consistent with animals without salivary amylase. Only Old World primates known as ceropithecines have evolved AMY1 (salivary alpha-amylase) to consume starches from fruit seeds that they carry in their cheek pouches.
RS2 Alone Burns FAST&FURIOUSLY in Proximal Colon; But, No Change in Stool pH
RS2 is butyrogenic, (mildly)bifidogenic and burns with smoking hawwt intensity at the caecum.
However, to flood the entire colon with health promoting butyrate, other plant fibers (including RS3) are needed to add bulk and carry the beneficial granules distally toward the rectum. In human
RS2 alone trials, stool pH failed to improve compared with controls indicating
that little fermentation occurred toward the end of the colon (here, here, here).
One experiment was 4 weeks and low fiber. These experimental diets used RS2
alone + NSP ~10 g/day, similar to that typically observed in low fiber S.A.D.,
Paleo, VLC or Atkins induction diets (e.g. 1 fruit + 100 g/day vegetable +
little legumes or whole grains). Conventional fiber is also known as NSP,
Two cups of romaine lettuce is ~ 2 g NSP fiber; one 7.5 inch carrot, 2.3 g.
High stool pH indicates a lack of both colon fermentation and butyrate flooding the
colon. More and more studies are showing that stool pH can be a reliable marker
for colorectal cancer (Walker et al 1986; Newmark, Lupton 1990).
Granular RS2 particles are covered with a brilliant number of constellations for
bacterial amylases to adhere and attack. On the other hand, crystalline RS3
matrices are gradually, slowly degraded with quite a lot of endearing and
sustained fermentation to the distal colon, unlike granular RS2 starch
(hat tip: Gemma).
“The starch granule size seemingly presents a
very favourable target for attack by amylase
with many potential sites for binding of the
enzyme. In spite of this apparent binding advantage, the
complete breakdown of starch within an intact granule is a
fairly slow process. Crystalline areas tend to be unfavourable
for enzyme attack and, in addition, the granules may
contain small but variable amounts of proteins and lipids
that can also hinder starch–amylase interaction. Most of
the starch consumed by humans will have been cooked
and/or subjected to various processes during food production
that disrupts the granules to a greater or lesser
extent, but raw starch is consumed in many animal feeds.
Processing that disrupts general granule integrity and
reduces the degree of crystallinity, increases the susceptibility
We like RS a lot. It’s an unconventional fiber, and synergistic with other gut fuel. Together, they are bionic nourishment that our intestinal cohabitants are intimately familiar with for tens of millenia, if
While technically correct that raw potato starch is a valid form of RS2, using it as a
sole source of RS for your gut microbes is probably not the best plan of action.
Looking back at studies that used just RS2, we see that RS2 is somewhat unique
in that in ‘burns fiery hot’ once it exits the small intestines. This means
that the RS2 granules are converted to short chain fatty acids SCFA, mostly
butyrate, in the cecum. SCFA and butyrate are mildly acidic and lower pH. In
many ways RS2 ‘behaves’ physiologically and biologically like soluble
fiber. Like pectin or gums, it does not bulk stools significantly compared with
non-soluble fibers or retrograded RS3.
RS3 Burns Perfectly Prolonged All the Way to the Distal End of the Colon
Cooked-cooled, retrograded RS3 starch is a insoluble, large matrix of crystalline
structures, and on the other hand, ‘burns slowly.’ It is insoluble and behaves like
insoluble fiber and architecture to soft stools and providing bulk by increasing
water holding capacity. I believe it provides a solid scaffolding for microbial
ecosystems to colonize and flourish.
Ever notice how hardly anyone complains of flatulence when eating RS3 rich foods such
as cooked and cooled potatoes and rice? This is probably due to the fact that
it is slowly fermented and the gasses produced are dealt with by gas-degrading
microbes in a timely fashion. We had originally taken the lack of gas to
indicate lack of performance, but this is wholly unfounded. The older ileostomy
studies prove conclusively that the RS3, formed from cooked and cooled starches,
arrives intact in the large intestine and modern microbe studies using 16s rRNA
sampling prove that RS3 has profound effects on the gut microbiota leading to all of the positive changes we desire.
studies on consumption of RS3 rich foods like beans and lentils show protection
as well as colon
In moderate fiber human studies (here,
the combination of RS3, RS2, RS1 (total 38 g/day) + NSP 20 g/day (including raw
green banana flour) was associated with significant improvements of every marker
of gut health, including the largest drop in stool pH recorded in human studies.
The lower and improved pH mark how microbiota fermentation and butyrate very
likely and consistently flooded the entire length of the colon to the distal
end. Also, dilution of ammonia and lower concentrations of fecal carcinogens
(p-cresol, phenols) were noted.
The mix of cooked RS3 and fiber produced outcomes that vastly contrast with the
human study where RS2 did not dilute ammonia, but retrograded RS3 did.
Therefore, we feel it prudent to not seek total intake of prebiotic, fermentable fiber from
isolated RS2 sources. A diet supplying very little fiber, regardless of total
carb count, and supplemented only with a refined RS2 (such as Bob’s Red Mill
potato starch or Hi-Maize corn starch) will not be nearly as healthful as it
could be if the RS2 was augmented with an array of other
Both insoluble fiber and RS3 are enriched in low GI starchy foods -- lentils, peas, legumes, whole GF grains. Other roots/vegs and tubers are also abundant in either RS3 (sago, cassava, taro, heirloom potatoes) or insoluble fuel (turnips, okra).
RS and Total Dietary Fiber
From the ancestral evidence and modern studies, just getting the USDA recommended
25g/day of fiber is not enough. More likely 40-80g/day would be optimal.
“Fiber” is such a fickle word...the fiber listed on nutrition labels is
considered TotalDietary Fiber which includes every type of fiber that resists digestion. Googling
for the information you can get ‘conventional fiber’ charts.
If you are concerned about the effect on blood glucoses (BG) and the glycemic load
on the above foods, be assured that all the above have low GIs (glycemic
indices) of ~20-50. Each meal contains 1 to 2 servings of carbs (15 net carbs)
and need to be adjusted and personalized based on individual insulin
sensitivity, exercise, diet, relaxation, stress, sleep, hormone status and health goals. PHD
is 150 g/day high GI ‘white’ carbs, in other words, ~10 servings carbs.
Fermenting (soaking) lentils and legumes completely changes the structure of the beans and unlocks many nutrients, cooking then enrihes insoluble fiber in addition to creating more resistant starch—besides making them edible. Cooling them crystallizes further resistant starch. Expanding on raw and cooked tubers and root vegetables, consuming a diverse and variety of plant fiber
(green banana/plantains, lentils, legumes, gluten-free grains, nuts) secures phytochemicals
which are anti-aging and cancer-protective antioxidants.