| I was so surprised to see this! A really well-written piece on RS, all
of the facts were right and she even mentioned me. Of course I just had
to jump in and help with the comments. I hope I didn't steal their
thunder, but I tried to leave the hard, medical questions to the experts. Some very good comments, go check them out. I think what amazed me more was the depth of the discussion. This shows me that people are taking gut health serious and looking at RS as a tool to achieve gut health and exploring the alternatives. Also some great comments by my partners in crime: Duck Dodgers, PaleoPhil, and Gemma! |
How Resistant Starch Will Help to Make You Healthier and Thinner
I asked Dr. Amy Nett, MD, to
contribute this guest post. She recently joined my private practice and
will be working with me in the clinic. Amy initially completed her
medical training in radiology at Stanford University Hospital, but
wanted to work more directly with patients, helping them to prevent and
reverse chronic disease and truly transform their health. Combined with
her passion for nutrition she decided to pursue a career in functional
medicine, and is excited to have the opportunity to work more closely
with patients in achieving their goals and realizing their best
potential. You’ll be hearing more from Amy in the future!
Over the past several years there has
been an exponential increase in the number of studies linking imbalances
or disturbances of the gut microbiota to a wide range of diseases
including obesity, inflammatory bowel diseases, depression and anxiety (1,2,3,4,5).
One of the best ways to establish and support a healthy gut microbiome
is by providing the right “foods” for your gut bacteria. These “foods”
are called prebiotics.
Why you should add resistant starch to your diet.
Prebiotics are indigestible
carbohydrates, or at least indigestible to us, that reach the colon
intact and selectively feed many strains of beneficial bacteria.
Prebiotics are generally classified into three different types:
non-starch polysaccharides (such as inulin and fructooligosaccharide),
soluble fiber (including psyllium husk and acacia fibers), and resistant
starch (RS). Each of these types of prebiotics feeds different species
of gut bacteria, but among these, RS is emerging as uniquely
beneficial.
The distinctive benefits of RS seem to be unequivocally recognized, even amongst advocates of a low carbohydrate diet.
What is resistant starch?
Resistant starch is a type of starch that
is not digested in the stomach or small intestine, reaching the colon
intact. Thus, it “resists” digestion. This explains why we do not see
spikes in either blood glucose or insulin after eating RS, and why we do
not obtain significant calories from RS.
There are four types of resistant starch:
RS Type 1: Starch is physically
inaccessible, bound within the fibrous cell walls of plants. This is
found in grains, seeds, and legumes.
RS Type 2: Starch with a high amylose
content, which is indigestible in the raw state. This is found in
potatoes, green (unripe) bananas, and plantains. Cooking these foods
causes changes in the starch making it digestible to us, and removing
the resistant starch.
RS Type 3: Also called retrograde RS
since this type of RS forms after Type 1 or Type 2 RS is cooked and then
cooled. These cooked and cooled foods can be reheated at low
temperatures, less than 130 degrees and maintain the benefits of RS (6).
Heating at higher temperatures will again convert the starch into a
form that is digestible to us rather than “feeding” our gut bacteria.
Examples include cooked and cooled parboiled rice, cooked and cooled
potatoes, and cooked and cooled properly prepared (soaked or sprouted)
legumes.
RS Type 4: This is a synthetic form of RS
that I’m including for completeness, but would not recommend. A common
example is “hi-maize resistant starch.”
Once RS reaches the large intestine,
bacteria attach to and digest, or ferment, the starch. This is when we
receive the benefits of RS.
How resistant starch impacts our health
The normal human gut has hundreds of
bacterial species, some good and some not so good. The overall number
and relative quantity of each type has a profound effect on our health
and well being. Resistant starch selectively stimulates the good
bacteria in our intestines, helping to maintain a healthy balance of
bacteria (7).
These good bacteria “feed” on RS and
produce short chain fatty acids (through fermentation), the most
significant of which are acetate, butyrate, and propionate. Of these
three short chain fatty acids (SCFA), butyrate is of particular
importance due to its beneficial effects on the colon and overall
health, and RS appears to increase butyrate production more when
compared with other soluble fibers (8).
Butyrate is the preferred energy source
of the cells lining the colon, and it also plays a number of roles in
increasing metabolism, decreasing inflammation and improving stress
resistance, as described in more detail below and previously in this great article by Stephan Guyenet.
Resistant starch helps to lower blood glucose levels and improve insulin sensitivity
Insulin resistance and chronically
elevated blood glucose are associated with a host of chronic diseases,
including metabolic syndrome. Several studies have shown that RS may
improve insulin sensitivity (9), and decrease blood glucose levels in response to meals (10, 11, 12).
In one study, consumption of 15 and 30 grams per day of resistant
starch showed improved insulin sensitivity in overweight and obese men,
equivalent to the improvement that would be expected with weight loss
equal to approximately 10% of body weight (13).
Further, RS has been shown to exert a
“second meal effect.” This means that not only does RS beneficially
decrease the blood glucose response at the time it’s consumed, but,
somewhat surprisingly, blood glucose and insulin levels also rise less
than would otherwise be expected with the subsequent meal (14).
Why the popular press has touted resistant starch as a “weight loss wonder food”
RS appears to have several beneficial
effects that may contribute to weight loss, including decreased blood
insulin spikes after meals (as discussed above), decreased appetite, and
decreased fat storage in fat cells. There may also be preservation of
lean body mass, though further studies in humans are needed to confirm
if there is a significant impact in overall body weight (15).
Further, several studies have shown
alterations in the gut microbiome in association with obesity, which
subsequently change towards that seen in lean individuals with weight
loss (16, 17). For example, one study demonstrated that the relative composition of the gut microbiota of two predominate beneficial bacteria, Bacteroidetes and Firmicutes, varied considerably in association with body composition. Specifically, obese individuals often have a higher proportion of Firmicutes to Bacteroidetes, which may be reversed with weight loss, gastric bypass surgery, or treatment with prebiotics (3).
However, not all studies confirm a significant or measurable change in
the composition of the microbiome in obese compared to lean individuals,
and further studies are needed (18, 19).
Butyrate plays an important role in gut health and decreasing inflammation in the gut and other tissues
As mentioned above, RS intake allows for
increased production of butyrate by our gut microbes. Butyrate acts as a
powerful anti-inflammatory agent for the colonic cells, and functions
to improve the integrity of our gut by decreasing intestinal
permeability and therefore keeping toxins in the gut and out of the
bloodstream. (20, 21).
The SCFAs that aren’t utilized by the
colonic cells enter the bloodstream, travel to the liver, and spread
throughout the body where they exert additional anti-inflammatory
effects.
Resistant starch is also associated with
decreased risk of colorectal cancer, thought to occur through several
different mechanisms including: protection from DNA damage, favorable
changes in gene expression, and increased apoptosis (programmed cell
death) of cancerous or pre-cancerous cells (22, 23).
Adding resistant starch to your diet
Some common food sources of RS include
green (unripe) bananas, plantains, properly prepared cooked and cooled
parboiled rice or legumes, and cooked and cooled potatoes. See this link for a more complete list of RS quantities in food.
However, if you are on a low carbohydrate
diet or don’t tolerate those foods well, you can add RS to your diet
without adding digestible carbohydrates.
Bob’s Red Mill Unmodified Potato Starch
(NOT potato flour) is one of the best sources of RS with approximately
eight grams of RS in one tablespoon. Potato starch is generally well
tolerated even by those who react adversely to nightshades.
Plantain flour and green banana flour are
also excellent sources of RS, and there may be benefit to including all
three of these sources (specifically alternating your source of RS
rather than relying on a single one).
These are relatively bland in flavor and
can be added to cold or room temperature water, almond milk, or mixed
into smoothies. But to maintain the benefits of RS, these should not be
heated above 130 degrees.
Tim Steele (Tatertot) has written
about some of the research on RS supplementation, and in particular the
potential further benefit of combining potato starch with psyllium husk
fiber to even further increase butyrate production in the colon.
Take it slow
If you choose to try supplementing with
RS, start with small doses of about ¼ teaspoon once daily, and very
gradually increase the amount as tolerated. Some increased gas and
bloating is expected as your gut flora changes and adapts, but you do
not want to feel uncomfortable. If you experience marked discomfort,
then decrease the amount you’re taking for a few days until your
symptoms resolve, and then try increasing again gradually.
Studies indicate that the benefits of
resistant starch may be seen when consuming around 15 to 30 grams daily
(equivalent to two to four tablespoons of potato starch). This may be
too much for some people to tolerate, particularly in the setting of gut
dysbiosis, and going above this amount is not necessarily beneficial.
If you experience marked GI distress with
even small amounts of RS, this may be an indication of SIBO (small
intestinal bacterial overgrowth) or microbial dysbiosis, and you may
need to consider working with a healthcare practitioner to establish a
more balanced gut microbiome through the use of herbal antimicrobials
and probiotics before adding RS or other prebiotics.
