Thanks for the perspective. For more perspective can you compare the the colonic processing of resistant startches to that of leafy vegetables?
So What Is Resistant Starch Anyway?
The common run of the mill starch that we are all familiar with is a long chain ( a polymer in chemistry terminology ) of glucose molecules occurring as either amylopectin or amylose in most plants. Proportionally speaking, starch is comprised of 2/3 amylopectin and 1/3 amylose. It turns out that structurally, amylopectin and amylose very closely resemble glycogen, so much so that one of the first informal names for glycogen was animal starch. This being the case, it should be of no surprise that human beings have no trouble in breaking off individual glucose molecules from the polymer via the amylase family of enzymes to use as an energy substrate.
When it comes down to how to make a glucose chain, you tend to be spoilt for choice since glucose is a 6 carbon molecule and each carbon has the capacity to form 4 bonds, giving us roughly 24 binding sites. In practice, however, the vast majority of bonds in amylopectin and amylose chains are formed between the first and fourth glucose carbon atoms ( 1-4 bonds ) while a very small portion of the bonds in amylose chains form between the first and last carbon atoms of the glucose molecule ( 1-6 bonds ).
The Many Flavours of Amylase
You may recall that I mentioned earlier that there is a family of amylase enzymes. There are in fact three variants: alpha, beta, and gamma amylase. All three variants are capable of breaking down glucose 1-4 bonds, but only gamma amylase can process 1-6 bonds. The reality for you, if you are a mammal, is that you only possess alpha amylase, so any starchy food that you eat which has 1-6 glucosidic bonds will pass through your stomach and small intestine and reach your large intestine intact. Or, in other words, 1-6 glycosidic bonds are "resistant" to your amylase.
What's So Great About Carbohydrates That Pass Intact Into the Large Intestine?
Well, in and of itself, nothing, really. However, you do have fairly substantial bacterial colonies in your colon, and it turns out that some of these can ferment various carbohydrates that make it through the digestive tract to reach them. The end products of this fermentation can include short chain fatty acids (SCFA) like acetate, propionate and butyrate, and those in turn serve to nourish the cells lining your colon. Any excess SCFAs are absorbed from the colon and oxidized by the host ( you ).
Some studies have associated colonic butyrate with decreased rates of colon cancer, so there may be something to be said for the occasional butyrate high colonic. But, does this mean that we need to go out of our way to consume indigestible carbohydrates in order to feed our intestinal mucosa?
All that Glitters is not Gold
Any fermentation that goes on in the large intestine occurs principally for the benefit of the bacterial fermentor, it is only incidental that the host ( you ) derives some benefit. Of the end products of fermentation there are two general categories: energetic compounds and wastes. The energetic compounds are extracted and retained by the fermenting bacteria, while the waste products are eliminated to the greater environment. Ultimately then, the SFAs being generated by fermentation are actually a waste product from the perspective of the fermentor. Given this, you might find yourself wondering about what other waste products might result? Typically, these include hydrogen, methane, carbon dioxide, and hydrogen sulfide gases.
Depending on your sense of humour, you might find this amusing, particularly if you find yourself at a posh dinner party where some other guest, hopefully someone you don't particularly like, is undergoing a significant amount of colonic fermentation. But if you reflect for a moment about the many individuals who are lactose intolerant and the degree of intestinal problems they experience from drinking, say, one glass of milk, you might find the prospect of colonic fermentation a bit more sobering.
Consider that in a lactose intolerant individual, the operative mechanism is a deficiency of the enzyme necessary to hydrolyze the lactose disaccharide into its constituent monosaccharides, glucose and galactose. As a result of this, lactose passes through the stomach and small intestine intact … at which point we pick up the earlier thread about the dubious benefits of carbohydrates passing intact into the large intestine.
Whole milk contains approximately 5% lactose, so a 200 ml glass would provide you about 10g of lactose. Which is to say that the difference between the lactose tolerant and someone who is forced to make a mad dash to the bathroom to undergo a bout of explosive diarrhea is a mere 10g of a resistant carbohydrate.
What if I'm Hell Bent on Colonic Fermentation?
You may be fortunate in that you are not lactose intolerant, but it is a safe bet that you are raffinose and stachyose intolerant because humans lack the galactosidase enzyme necessary to metabolize these oligosaccharides. Since you cannot enzymatically process either raffinose or stachyose, these carbohydrates are "resistant" to your digestive efforts.
Beans are relatively high in both of these sugars, so in order to simulate the effects of a 10g lactose load in a lactose intolerant individual you would need to eat 1kg of cooked beans. Of course, for the truly hardcore, don't cook your beans, and you triple the oligosaccharide dose per bean, so only 300g needed … be advised that you may come to hate your bowel movements, however.
Alternatively, since there does seem to be an infatuation with all things potato of late, you could attempt to do this by eating 2.4 kilograms of cold cooked potatoes. If you insist on eating your potatoes warm, however, you're then looking at approximately 5 kgs of potatoes, or 11 lbs. worth.
But Butyrate is Really Good, No?
Actually, yes, butyrate is a reasonably beneficial short chain fatty acid. But there is more than one way to skin the butyrate cat. If we are intent on getting some butyrate in the colon, then the trick is to find some way to bypass digestion and have carbohydrates made available for the intestinal microflora to ferment, but I'll save that for a later post.
Thanks for the perspective. For more perspective can you compare the the colonic processing of resistant startches to that of leafy vegetables?
Four years Primal with influences from Jaminet & Shanahan and a focus on being anti-inflammatory. Using Primal to treat CVD and prevent stents from blocking free of drugs.
Eat creatures nose-to-tail (animal, fowl, fish, crustacea, molluscs), a large variety of vegetables (raw, cooked and fermented, including safe starches), dairy (cheese & yoghurt), occasional fruit, cocoa, turmeric & red wine
Great post, thanks for breaking that down.
That's quite a dissertation there, but I'm not sure what you are getting at.
Many of the items you refer to are not resistant starches (RS), such as milk and bean sugars. These are sugars that are supposed to be digested in the small intestine, but when someone lacks the capacity to digest them there, they end up in the colon where they are fermented into unwanted and sometimes harmful chemicals.
RS is actually a family of 4 types of RS...
RS1 Physically inaccessible or digestible resistant starch, such as that found in seeds or legumes and unprocessed whole grains
RS2 Resistant starch that occurs in its natural granular form, such as uncooked potato, green banana flour and high amylose corn
RS3 Resistant starch that is formed when starch-containing foods are cooked and cooled such as in legumes, bread, cornflakes and cooked-and-chilled potatoes, pasta salad or sushi rice. The process of cooking out the starch and cooling it is called retrogradation.
RS4 Starches that have been chemically modified to resist digestion. This type of resistant starches can have a wide variety of structures and are not found in nature.
These are all true starches that do not digest in anybody's small intestine. Never have, never will. Our colon bacteria have evolved on them and need them for survival. Proof of that is the specialized colonocytes that feed off the butyrate produced by the gut bacteria.
The typical SAD provides about 2-3g per day of RS, the typical LC Paleo provides about zero. I have seen studies that ancestral diets provided about 50g/day, mostly RS-1 and 2 from raw tubers and seeds. Most health boards think the optimal amount is 20-30g/day, but almost no one gets that without trying really hard.
I have no idea what this means...a typical raw potato, about 1/2 pound, contains about 30g of RS2. Cooked, it contains about 3g RS2. Cooked and cooled 9g RS3. A small green banana contains about 5g RS2.Alternatively, since there does seem to be an infatuation with all things potato of late, you could attempt to do this by eating 2.4 kilograms of cold cooked potatoes. If you insist on eating your potatoes warm, however, you're then looking at approximately 5 kgs of potatoes, or 11 lbs. worth.
So, eating 1 potato a day puts you back to SAD levels of RS, eating 1 regular potato, 1 potato cooked and cooled, and a couple slices of raw potato puts you almost at the recommended range.
A couple of studies for you to check out, not that they are a smoking gun for RS, but just to show the extent of research into RS:
Which says in part:
http://scholar.lib.vt.edu/theses/ava...d/ALDfinal.pdfBecause resistant starch (RS) is not absorbed in the small
intestine of healthy individuals (1), but is partly fermented in the
colon, it may have positive effects on putative risk factors for
colon cancer by analogy with dietary fiber. Colonic fermentation
of RS may lead to the production of short-chain fatty acids
(SCFAs) (2–4). Some studies indicate that fermentation of RS
leads specifically to an increase in butyrate (5–7). Butyrate putatively
has a protective effect against colon cancer (8–11).
(Password protected thesis, can't cut-n-paste)
Effects of resistant starch on the colon in healthy volunteers: possible implications for cancer prevention.
Recent evidence suggests that resistant starch (RS) is the single most important substrate for bacterial carbohydrate fermentation in the human colon.
I have plenty more, but don't want to turn this into a 'I have more studies than you' situation. The bottom line is, we know that a healthy gut microflora is very important to overall health, special cells in the colon feed on butyrate produced from RS in the colon, and RS is a special starch and not just anything that happens to end up in the colon [insert funny joke here].
Ingested butyrate doesn't make it to the colon so has no effect on colonocyte health.
I wonder if one takeaway here isn't that one absolutely needs to consume RS, but rather that we've collectively drifted away from high-RS carb sources to what Ian Spreadbury calls "acellular" carbs that cause great upheaval in gut flora further up the line (small intestine). I'm really attracted to the idea that this could be part of a unifying explanation of why people can thrive over such a broad range of carb intake on ancestral diets that exclude industrialized flours & refined sugars but retain varying levels of minimally processed tubers, fruit, even rice.
6' 2" | Age: 42 | SW: 341 | CW: 198 | GW: 180?
“Life can only be understood backwards, but it must be lived forwards.”
― Søren Kierkegaard
What is your point?
Dietary fibre improves first-phase insulin secretio... [PLoS One. 2012] - PubMed - NCBI
I find the evidence so overwhelming that RS is a much needed nutrient. Why anyone would argue against it is beyond me. The solution is quite simple, too: a few, very primal, RS sources added to your diet like potato and rice, and not in the quantities suggested above, but like 1 potato or a serving of rice. Double-down by cooking and cooling, triple-down by eating the potato raw...Previous work has shown increased insulin sensitivity, increased hepatic insulin clearance and lower postprandial insulin responses following treatment with resistant starch, a type of dietary fibre. The objective of this study was to further explore the effects of resistant starch on insulin secretion. Twelve overweight (BMI 28.2±0.4 kg/m(2)) individuals participated in this randomized, subject-blind crossover study. Participants consumed either 40 g type 2 resistant starch or the energy and carbohydrate-matched placebo daily for four weeks. Assessment of the effect on insulin secretion was made at the end of each intervention using an insulin-modified frequently sampled intravenous glucose tolerance test (FSIVGTT). Insulin and C-peptide concentrations were significantly higher during the FSIVGTT following the resistant starch compared with the placebo. Modelling of the data showed significantly improved first-phase insulin secretion with resistant starch. These effects were observed without any changes to either body weight or habitual food intake. This study showed that just four weeks of resistant starch intake significantly increased the first-phase insulin secretion in individuals at risk of developing type 2 diabetes. Further studies exploring this effect in individuals with type 2 diabetes are required.
And this one: http://www.ncbi.nlm.nih.gov/pubmed/21963168BACKGROUND & AIMS:
OK, it's rats, but still...Population studies indicate that greater red meat consumption increases colorectal cancer risk while dietary fibre is protective. Previous work in rats showed that diets high in protein, including red meat, increase colonocyte DNA strand breaks and that this effect is attenuated by resistant starches (RS). Telomeres are long hexamer repeats that protect against spontaneous DNA damage which would lead to chromosomal instability. Telomere shortening is associated with greater risk of colorectal cancer. The current study aimed to determine the effects of cooked red and white meat intake on colonocyte telomere length in rats and whether dietary RS modified their effects.
After four weeks of feeding cooked beef or chicken at 15, 25 and 35% of diet with or without RS, colonocyte telomere length was measured.
Telomere length decreased in proportion to red meat content of the diet. A similar trend was observed in the white meat group. Colonocyte telomere shortening due to increased dietary meat was attenuated by the inclusion of RS.
These data support previous findings of increased colonocyte DNA damage with greater red and white meat intake and also the protective effect of dietary fibre.
Precision Nutrition » All About Resistant Starch
Summary: Resistant starch is a type of starch that isn’t fully broken down and absorbed, but rather turned into short-chain fatty acids by intestinal bacteria. This may lead to some unique health benefits. To get the most from resistant starch, choose whole, unprocessed sources of carbohydrate such as whole grains, fruits, vegetables, and beans/legumes.
What makes a starch “resistant”?
RS is similar to fibre (see All About Fibre), although nutrition labels rarely take RS into account.
SCFAs and RS
When RS is fermented in the large intestine, short chain fatty acids (SCFA) such as acetate, butyrate, and propionate, along with gases are produced. SCFAs can be absorbed into the body from the colon or stay put and be used by colonic bacteria for energy.
Evidence suggests that SCFAs may benefit us in many ways. For instance, they:
stimulate blood flow to the colon
increase nutrient circulation
inhibit the growth of pathogenic bacteria
help us absorb minerals
help prevent us from absorbing toxic/carcinogenic compounds
The amount of SCFAs we have in our colon is related to the amount and type of carbohydrate we consume. And if we eat plenty of RS, we have plenty of SCFAs.
Rate of digestion changes absorption
Since RS is incompletely digested, we only extract about 2 calories of energy per gram (versus about 4 calories per gram from other starches). That means 100 grams of resistant starch is actually only worth 200 calories, while 100 grams of other starch gives us 400 calories. High-RS foods fill you up, without filling you out.
The way we’ve modified/processed grains and starchy vegetables in the modern food supply diminishes the amount of RS we consume (think: cereal bars instead of oats, burgers instead of beans, potato chips instead of boiled potatoes). And fibre sources such as wheat bran, psyllium, and methyl-cellulose (Citrucel) don’t have the same benefits.
Thus, to get the most benefits from RS, we need to consume it in whole food format.
Most developed countries (including Europe, the United States, New Zealand, and Australia), which have a highly processed diet, consume about 3-9 grams of RS per day. In developing countries, diets are often based around whole plant foods and the intake of RS tends to be around 30-40 grams per day.
Potential benefits of RS
Improved blood fats
RS may help to lower blood cholesterol and fats, while also decreasing the production of new fat cells (the latter has only been shown in rats). Also, since SCFAs can inhibit the breakdown of carbohydrates in the liver, RS can increase the amount of fat we utilize for energy.
RS can help us feel full. SCFAs can trigger the release of hormones that reduce the drive to eat (leptin, peptide YY, glucagon like peptide). After someone starts eating more RS, it may take up to one year for gut hormones to adapt.
RS slows the amount of nutrients released into the bloodstream, which keeps appetite stable.
Better insulin sensitivity
RS doesn’t digest into blood sugar, which means our bodies don’t release much insulin in response.
RS might also improve insulin sensitivity via alterations in fatty acid flux between muscle and fat cells. Some data indicate that ghrelin might increase with RS consumption, improving insulin sensitivity (this is counterintuitive since ghrelin drives appetite). RS may also lower blood fats (see above), which also improves insulin sensitivity.
RS may help alleviate irritable bowel syndrome, diverticulitis, constipation, and ulcerative colitis. RS can add bulk and water to the stool, aiding in regular bowel movements.
SCFAs can help to prevent the development of abnormal bacterial cells in the colon and enhance mineral absorption (especially calcium).
Better body composition
Since RS has less energy (calories) per gram than other starches, it can help us eat less. And consuming more RS may have a thermic effect in the body.
Keeping us hydrated
For those receiving treatment for cholera and/or diarrhea, RS can assist in the rehydration process (since it can normalize bowel function).
RS is found in starchy plant foods such as:
starchy fruits and vegetables (such as bananas)
some types of cooked then cooled foods (such as potatoes and rice)
The longer and hotter a starch is cooked, the less RS it tends to have — except for Type 3 RS.
Types of resistant starch
Type 1: Physically inaccessible Type 2: Resistant granules
Cannot be broken down by digestive enzymes.
Found in: legumes, whole and partially milled grains, seeds.
Intrinsically resistant to digestion and contains high amounts of amylose.
Found in: fruits, potatoes, hi-maize RS products, corn, some legumes.
Note: the more “raw” or “uncooked” a food is, the more RS it tends to have, since heat results in gelatinization of starch – making it more accessible to digestion. Type 3 starch is the exception to this rule.
Type 3: Retrograded Type 4: Chemically modified
When certain starch-rich foods are cooked and then cooled, the starch changes form, making it more resistant to digestion.
Found in: cooked/cooled foods like potatoes, bread, rice, cornflakes.
Companies have isolated RS (usually from corn) to include it in processed foods (e.g., breads, crackers, etc.).
This is not naturally occurring RS — it’s produced mostly via chemical modification, and it’s found in synthetic and commercialized RS products, such as “Hi-Maize Resistant Starch”.
How much RS should we consume?
Data indicates that RS is safe and well tolerated up to about 40-45 grams per day. Consuming more than this might result in diarrhea and bloating, since high amounts can overwhelm the fermenting ability of our colonic bacteria.
How we respond to RS varies by the type. One might notice more side effects when consuming RS3 (versus RS1, RS2, RS4). Our ability to ferment RS can increase over time, making it possible to adapt to a higher RS intake.
RS seems to be tolerated best when:
It’s in solid food form (rather than liquid)
It’s consumed as part of a mixed meal (rather than alone)
Consumption is increased gradually over time (rather than a lot at once)
Here’s an idea how much RS is found in food. Note: these are average values and will vary.
Grams of RS per 100 g of food
Resistant Starch Chart 551x1024 All About Resistant Starch
Summary and recommendations
We absorb more energy (calories) from cooked and highly refined and processed carbohydrate dense foods. If we let machines and ovens do the digestion for us, we are left with highly digestible starches. Not good for glucose control, staying lean, or intestinal health.
Various cultures thrive and stay lean when eating whole unprocessed legumes, intact grains and starchy vegetables. RS may be one factor that enables this.
We might see some benefits from as little as 6-12 grams/day of RS, but closer to 20 grams/day might be ideal. This is easy to get if you eat plenty of whole plant foods.
More than 40 grams/day might cause digestive problems — especially if this RS comes from industrially produced RS products. In any case, we probably don’t get the same benefits of RS if it’s processed (i.e. an industrially created RS product) as we do from whole foods.
Last edited by otzi; 01-16-2013 at 03:25 PM.
OK, I promise no more links, after this one...
All the studies you ever wanted to see on RS, find one that says it's not needed and I'll back off.
dietary resistant starch: Topics by WorldWideScience.org