Carbs: Resistant Starch (RS)

Green Bananas

by Catherine M. Haug,  Mar 2015; updated April 2019; Image, right, from Livestrong (11)

All starches are comprised of two types of glucose-to-glucose bonds:

  • Branched-chain amylopectin bonds  are the main constituents in regular starch; they are quickly and easily broken by the amylase enzyme in our small intestine.
  • Straight chain amylose bonds have less available surface area for the action of the amylase enzyme, so are digested much more slowly.

The more amylose bonds present in the starch, the greater its resistance to digestion; in other words, RS has a higher percentage of amylose than amylopectin than regular starch. (8) Green bananas are a great example.

Fiber

Within the carbohydrate category of fiber, we have long recognized two unique types that have different benefits for humans:

  • Soluble fiber, such as pectin; this type is digested by our gut bacteria
  • Insoluble fiber, such as those in whole grains; this type passes out with our stool, but not before cleaning our intestines like a brush.

More recently a third type of fiber has been discovered, that has properties of both soluble and insoluble fiber, called “Resistant starch” (RS). It is not easily digested (resists digestion) and instead serves as food for gut flora that produce short-chain fatty acids that heal and protect the colon. It has half the calories of regular starch. One of the most important short chain fatty acids produced by the bacteria that digest RS is butyrate (see Butyrate for more about this fatty acid).

Calories for the three types of dietary carbs:

  • Sugar and starch provide 4 calories per gram (from the component sugars, all of which are digested to provide the calories); 
  • RS provides approximately 2 calories/gram (only about half of the component sugars are digested, to provide calories); the remainder are converted to fatty acids); 
  • Fiber provides 0 calories/gram (its sugars are mostly converted to fatty acids or pass from the colon with the stool).

Resistant starch (RS)

4 types of RS: 

  • Type 1 which is physically inaccessible or indigestible in un-germinated seeds.  It is in unprocessed seeds including grains and legumes but other seeds too. Ground flax seeds are in this type. (See below about  pre-soaking or fermenting the seeds retains the RS.
  • Type 2 is in raw potatoes, plantain & green bananas. Cooking this type turns RS into regular starch. NOTE: all of these are available in a flour-like raw form.
  • Type 3 results when foods like potatoes or rice are cooked and then cooled, which turns the starch back into RS unless heated again. 
  • Type 4 RS is made synthetically.

Regarding pre-soaking or fermenting type-1 RS:

Does presoaking or fermenting (sourdough) whole grains preserve the resistant quality of RS? One study concludes, “Sourdough fermentation of rye bread was found to have a greater impact on resistant starch formation than bulk fermentation of wheat and wheat blend breads, most likely due the increased organic acid content of the sourdough process.“ (7)

Benefits RS

All of the RS-types are said to greatly improve insulin sensitivity, and also to heal an inflamed colon, primarily through the action of the short-chain fatty acids such as Butyrate produced by bacterial fermentation of RS in the colon.

RS is also important because of its effect on lipid metabolism and lipid oxidation; it may help to lower stored body fat, also due to the effect of the short-chain fatty acids produced by bacterial fermentation of RS in the colon. See also Resistant starch consumption promotes lipid oxidation (2), to prevent fat accumulation long term, and Chris Kresser on Resistant Starch (4).

Another benefit of consuming resistant starch, is that it may help to rid the small intestine of ‘bad’ bacteria (or misplaced good bacteria); these bacteria attach to the resistant starch as it moves through the small intestine and into the colon where it is then flushed out of the colon with the stool. (10)

RS is tolerated best when (8):

  • It is in solid food form (rather than liquid);
  • It is consumed as part of a mixed meal (rather than alone);
  • Consumption is increased gradually over time (rather than a lot at once).

Calories in RS

Regular starch has the same number of available calories per gram as sugar at 4 calories/gram, but because RS starches resist digestion (and hence absorption), they only provide about half the available calories of regular starch, or 2 calories/gram. This is because roughly half of the RS is converted to short chain fatty acids by intestinal bacteria, leaving the other half to be broken down into absorbable simple sugars.

In general, processed foods are low in RS and are thus more caloric than minimally processed foods.

For comparison, calories for the three types of dietary carbs:

  • Sugar and starch provide 4 calories per gram (from the component sugars, all of which are digested to provide the calories); 
  • RS provides approximately 2 calories/gram (only about half of the component sugars are digested, to provide calories); the remainder are converted to fatty acids); 
  • Fiber provides 0 calories/gram (its sugars are mostly converted to fatty acids or pass from the colon with the stool).

Food sources and amounts of RS

Potato: Bob’s Red Mill raw potato starch is type 2 RS (dried at low temp), and can be added to smoothies or mixed with water/juice. It has is the highest content RS of any food. To use this, start with just 1 Tbsp/day and slowly work up to 4 Tbsp/day. It can take a couple weeks for its good effects to become noticeable. This info is from Authority Nutrition (1).

  • The powder provides 8 grams RS perTbsp
  • A whole raw potato is 13% RS provides 0.15 grams RS per 1 gram raw potato
  • 600 grams of baked, then cooled, potato has about 25 grams RS (starchy potato, like a russet). When cooks, the amount of RS drops by 90% or more; allowing it to cool restores a portion of the RS (11)

Green Plantain & Green Banana:

Whole: These are about 50% RS by weight in their unripened state (12) [I assume this is after they are peeled]. A whole average size green banana is pretty much going to be 10-30g of resistant starch, depending upon size and degree of ripeness. (12)

  • 1 large (8 inch) green, fully unripe banana has somewhere between 20-25 grams.
  • A large green plantain has about 50 grams (11).

The way to peel these is different from peeling a ripe banana: Cut the fruit lengthwise, then remove the fruit.

Flour: green plantain and green banana are available in flour form (4). I’ve not seen these in local grocery stores, but they are available on Amazon. Free The Animal (12) says green banana flour has better flavor than plantain flour, and recommends WEDO brand.

  • ¼ cup green banana flour (uncooked) provides 10.5 – 13.2 g RS (13a); Banana flour has a high resistant starch content (17.5%) [this translates to about 0.2 g RS per gram of banana flour; (13b)
  • Plantain flour: assuming it is similar to banana flour in RS content (but ¼ cup weighs only 30 g):  5.25 gram RS in about ¼ cup (30 g) plantain flour, or 1.3 grams RS in about 1 Tbsp plantain flour. (15).

Seeds: All whole seeds including grains and legumes contain RS, but modern processing methods reduce the availability of RS, as does cooking the seeds and consuming them when hot.

I grind my own flax seeds in small quantities so they don’t get heated, to retain the RS component, then add the ground flax to my morning smoothie. I’m currently avoiding high-carb foods which includes grains, but I may alter this to include high RS grains.

Teff, a gluten-free cereal grain, is high in type-1 RS (20-40% of the carbohydrates in teff are resistant starches). In Ethiopia, teff is usually ground into flour and fermented to make the spongy, sourdough bread known as injera. (6). According to Bob’s Red Mill, teff can be substituted for up to 25% of the all-purpose white flour in a recipe (5).

  • Teff pasta: 1 cup provides 1.4 g RS when cooled after cooking.

Legumes: 100 grams of hummus has 4.1 grams of RS. Hummus made from soaked chickpeas will have more than hummus made from canned chickpeas. (11)

  • green peas: 1 cup frozen, cooked and cooled green peas provides 4 g RS (13)
  • white beans: ½ cup, cooked and cooled provides 3.7 g RS (13)
  • lentils: ½ cup cooked & cooled lentils provides 2.5 g RS (13)

Type-4 RS (synthetic form of RS):

Food science has developed high-amylose cornstarch (type 4 RS), but most commercial sources are GMO and I would advise avoiding this.

Cat’s experiment with RS

I’m hoping to improve insulin sensitivity, and improve the microbial makeup of my intestines by increasing my intake of food-based RS while I’m otherwise following a ketogenic eating plan..

Beginning March 20, 2015 (during breaking the fast after a 5-day juice fast which cleaned out my colon), I started to add 1 Tbsp potato starch to morning smoothie, and will slowly work up to 2 Tbsp per smoothie and to add another 2 Tbsp in other ways during the day for total of the recommended 32 g RS daily.  I’ve ordered a bag of plantain flour, so I can alternated between potato and plantain starch, so that hopefully I don’t develop a sensitivity to either. I should see beneficial results of this regimen in 3 – 5 weeks.

When my plantain flour order arrived, I started with 1 tsp, with intent to work up to 1 Tbsp, along with the potato starch and fresh green banana. I didn’t notice any significant change from these, so when I’d used up what I had, I stopped.

March 2019: I discovered ButyCaps and started adding that to my morning smoothie. This was about a year after I started adding myo-inositol powder to my smooth (which had amazing benefits), so it’s hard to know if the ButyCaps are helping, but I’ll continue with it for a few months.

References: 

  1. Authority Nutrition (authoritynutrition.com/resistant-starch-101
  2. Journal of Nutrition & Metabolism: (www.ncbi.nlm.nih.gov/pmc/articles/PMC526391)
  3. Whole Health Source:  (wholehealthsource.blogspot.com/2009/12/butyric-acid-ancient-controller-of.html)
  4. Chris Kresser: chriskresser.com/how-resistant-starch-will-help-to-make-you-healthier-and-thinner 
  5. Livestrong: Baking with Resistant Starch (ivestrong.com/article/555770-baking-with-resistant-starch
  6. Whole Grains Council, on Teff and Millet (wholegrainscouncil.org/whole-grains-101/teff-and-millet-november-grains-of-the-month)
  7. The Effect of Fermentation and Addition of Vegetable Oil on Resistant Starch Formation in Wholegrain Breads – ResearchGate. Available from: researchgate.net/publication/272175788_The_Effect_of_Fermentation_and_Addition_of_Vegetable_Oil_on_Resistant_Starch_Formation_in_Wholegrain_Breads [accessed Mar 23, 2015].
  8. Precision Nutrition on Resistant Starch (precisionnutrition.com/all-about-resistant-starch)
  9. Study of butyrate-producing bacteria:
    1. in swine: ncbi.nlm.nih.gov/pmc/articles/PMC3675948/, and of
    2. butyrate-producing bacteria fed different carbohydrates in vitro: ncbi.nlm.nih.gov/pubmed/23909466 
  10. Mark’s Daily Apple:
    1. The Definitive Guide to Resistant Starch: marksdailyapple.com/the-definitive-guide-to-resistant-starch/#axzz3VkMHRMww  and eatingoffthefoodgrid.blogspot.com/2013/10/resistant-starch-and-sibo.html 
    2. marksdailyapple.com/resistant-starch-your-questions-answered
  11. livestrong.com/article/507166-green-bananas-health-benefits/
  12. Feed The Animal: freetheanimal.com/2014/02/bananas-resistant-starch.html 
  13. Wikipedia: en.wikipedia.org/wiki/Resistant_starch 
  14. Jamaican Choice Plantain Flour
  15. Amazon, on WEDO brand green banana flour
  16. Resistant Starch in Foods table: freetheanimal.com/wp-content/uploads/2013/08/Resistant-Starch-in-Foods.pdf
  17. Mercola:
    1. articles.mercola.com/sites/articles/archive/2018/04/30/digestive-resistant-starches.aspx

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