Frequently Asked Questions
There are a lot of details surrounding resistant starch. Hopefully, these questions will answer most of the basic information. If you want to ask something else, please send me your question.
What is resistant starch?
Resistant starch is simply starch (chains of glucose) that resists digestion in the small intestine. It reaches the large intestine, where it is consumed by the organisms of the microbiome within the large intestine. The official definition is “Resistant starch is the sum of starch and products of starch degradation not absorbed in the small intestine of healthy individuals” (Asp, NG Eur J Clin Nutr 46 Suppl 2 (1992): S1.)
→ This is a physiological definition – many different types of starches and starch fragments can be called “resistant starch”.
Are there different types of resistant starch?
Many different types of starch resist digestion for different reasons. Four different classes of resistant starch are widely recognized.
RS1 = starch that is physically trapped within a food matrix, which slows down the enzymes from digesting the starch. Intact whole grains or mildly processed foods contain RS1 resistant starch.
RS2 = crystalline starch that resists digestion while still in the native granule produced by the plant. The crystallinity of the glucose chains slows down digestion. Intact whole grains, raw potatoes, green bananas and high amylose corn contain RS2 resistant starch.
RS3 = retrograded starch that is created when starch is cooked and cooled. The glucose chains are released upon cooking, but some of them crystallize and form bonds that slow down digestion. Cooked and cooled bread, potatoes, rice or pasta contain small percentages (could be around 10%) of RS3 resistant starch.
RS4 = chemically modified starch which cannot be digested or is slowly digested. Different types of chemical treatments introduced different types of bonds, which change the characteristics of modified resistant starch.
What foods contain resistant starch?
Many different types of food contain resistant starch. Intact whole grains, beans, under-ripe/green bananas, raw potatoes, and high amylose grains are excellent sources of RS1 and RS2 resistant starch. Cooked and cooled starchy foods also contain modest levels of RS3 resistant starch.
Some processed foods have also been manufactured to contain resistant starch from different sources, including RS1, RS2, RS3 and RS4.
What are the side effects?
Some people experience a mild increase in flatulence after eating resistant starch, especially at higher doses (20 grams or more/day). Natural resistant starches are large, insoluble starch granules that ferment very slowly throughout the entire length of the intestinal tract. The physical structure of the starch granule ensures that the bacteria cannot digest the entire food source quickly.
Other types of prebiotic fibers are soluble, i.e., inulin and oligosaccharides, which means they are available for fast fermentation by the intestinal bacteria. The dose tolerance of these types of fibers is generally recognized to be 10-15 grams/day. Some people may be more sensitive to the fast fermentation of oligosaccharides, depending upon the composition of their microbiota.
In contrast, the dose tolerance for insoluble RS2 resistant starch is more than 30 grams/day. One study concluded that the dost tolerance was 45 grams/day (Kendall presentation, 2003).
How can I use resistant starch at home?
There are three ways to get resistant starch at home:
- Eat foods that contain resistant starch.
- Use resistant starch as a dietary supplement – mix it into smoothies, yogurt or oatmeal.
- Use it as a food ingredient – substitute a heat stable resistant starch for up to approximately 20% of the flour in most recipes.
Does resistant starch thicken like regular starch?
It depends on the source. RS2 from high amylose resistant corn starch, RS3 and RS4 will not thicken because it does not cook out like regular starch. It will not thicken gravy or sauces. If raw potato starch or green banana flour is used, it will cook out and provide thickening when heated but the resistant starch will be lost.
Can I bake with resistant starch?
It depends upon which type of resistant starch you utilize. Green banana flour (RS2) and potato starch (RS2) loses its resistance when it is cooked, but high amylose corn starch (RS2) and chemically modified RS4 retains its resistant starch through baking processes. High pressure and high temperature food processing (i.e., in cereal manufacturing) causes RS2 to lose their resistance, but RS4 can withstand high temperature and high pressure food processing.
How do I use resistant starch in cooking/baking?
Substitute about 20% of the flour in recipes for RS2 resistant starch from high amylose corn (which retains its resistance through baking). If your recipe calls for 1 cup of flour, use a little bit less of ¼ cup of resistant starch and a little bit more than ¾ cup of flour. Most recipes will look and taste the same.
If you use resistant starch in baking bread, gluten must be added to replace the gluten lost from the flour taken out of the recipe.
If you use resistant potato starch (RS2) or green banana flour (RS2), the resistant starch will be lost in the baking process – it becomes highly digestible and loses its resistance.
Where can I find recipes?
Two resistant starch cookbooks have been published: The CarbLovers Diet by the editors of Health magazine and The Skinny Carb Diet by David Feder and the editors of Prevention magazine. In addition, several recipes are available at www.KingArthurFlour.com, who sells Hi-maize® natural fiber.
What are the sources of isolated and extracted resistant starch?
High amylose corn, green banana flour, and raw potato starch are the most common sources of unmodified RS2 resistant starch. High amylose wheat is also being developed and may be available in the near future.
Raw potato starch is commonly referenced by many users online. It should be used as a supplement, as it loses its resistant starch and cooks out when heated or processed.
There are a couple of different sources of green banana flour in the market. The typical flour has been heat treated to dry, which degrades the resistant starch content. One brand, NuBana N200 Green Banana Flour from International Agriculture Group, has the highest levels of resistant starch available. It is just starting to become available in the market and has twice the amount of resistant starch as other sources of green banana flour.
What types of resistant starch are being used in the food industry?
There are several manufacturers which make and sell different types of resistant starch from a variety of sources:
- International Agriculture Group sells NuBana® green banana flour (RS2).
- Ingredion sells high amylose resistant corn starch (RS2) as Hi-maize® resistant starch and PenFibe® modified resistant potato starch (RS4).
- Cargill/Cerestar sells high amylose resistant cornstarch (RS2), ActiStar® resistant tapioca starch (RS3) and ActiStar® modified resistant tapioca starch (RS4).
- MGP Ingredients sells Fibersym® chemically modified wheat starch (RS4).
- Roquette sells Nutriose® resistant corn dextrin, a soluble fiber which they have started calling a resistant starch. While it technically meets the official definition as a product of starch degradation, this ingredient is not a starch and has very different properties than other types of resistant starch.
Is resistant starch from one source the same as resistant starch from another source?
It depends on the source and type. Starch is simply chains of glucose but the physical properties of the starch can vary tremendously. Unmodified and natural resistant starch from different sources are most likely very similar in their health effects, but may have different processing characteristics.
Chemically modified resistant starch will have different processing characteristics and may have different health effects. Not enough research has been done on the different types of chemically modified starches and dextrins to identify their health effects.
What is the microbiome?
Millions of bacteria and other organisms live in and on our bodies. They are collectively called the “microbiome”. The largest microbiome in our bodies lives in the large intestine, where they assist in digesting food, manufacturing vitamins. Recent research is showing that the gut microbiome has a very strong role in maintaining a healthy metabolism.
Where does my microbiome come from?
When babies are born, they receive their initial bacteria from their mother. Breast milk contains resistant sugars called oligosaccharides, which also feed the beneficial bacteria. As the child grows, their microbiome changes as their foods changes, they are treated with antibiotics, live in different geographical regions, etc. Your specific microbiome may be as individual as your fingerprint.
Which bacteria are beneficial?
There are millions of different strains and types of bacteria in our gut. It is very hard to say which strains and types of bacteria are the most beneficial.
Very commonly, Bifidobacteria and Lactobacillus have traditionally been identified as beneficial bacteria, because babies fed breast milk have higher levels of these bacteria. Researchers have also identified additional strains that seem to be correlated with beneficial health effects, including Ruminococcus bromii, Akkermansia muciniphila among others.
Can I improve my microbiome?
Yes, you can eat foods that are naturally fermented – i.e., yogurt, kefir, sauer kraut, etc. You can also eat foods that contain fermentable fibers – whole grains, bananas, onions, garlic and many other foods contain resistant starch, and oligosaccharides.
Can I measure my microbiome?
Yes, you can. An open sourced project at the University of Colorado will quantify your specific microbiome. Learn more at The American Gut Project. You could even try measuring it once, eating a lot of resistant starch for a week or two and measuring it again. There’s nothing like data to see how your diet changes how your body works!
Do I need to eat more fiber?
Yes, everybody needs to eat more fiber. Health authorities recommend that American women should consume 28 grams of dietary fiber/day and American men should consume 35 grams/day. On average, American women eat 14 grams and American men eat around 16 grams/day. In short, we need to double the amount of dietary fiber for optimal health. As different types of dietary fiber offer different benefits, people should eat a wide variety of dietary fibers for overall health.
Is resistant starch a type of dietary fiber?
Resistant starch has been called the third type of dietary fiber. The other two types are soluble and insoluble dietary fiber. While natural resistant starch is insoluble, it ferments within the body like soluble dietary fiber.
What do dietary fibers do?
There are three primary mechanisms of dietary fiber: (1) bulking, (2) viscosity or thickening, and (3) fermentation.
- Bulking fibers hold a lot of water and are most often described as roughage – i.e., cellulose from plant cell walls, wheat bran, psyllium. They are generally minimally fermented and are commonly used to help promote regularity.
- Viscous fibers thicken the contents of the intestinal tract and slow down the absorption of nutrients – i.e., beta-glucan from oats and barley, psyllium. They reduce the absorption of cholesterol and sugar in direct proportion to their thickening effect. They may or may not be easily fermented.
- Fermentable fibers are readily consumed by the gut microbiome, which may set off a cascade of health effects. Resistant starch, inulin, oligosaccharides are the best known fermentable fibers to date.
What is a prebiotic fiber?
Some types of dietary fiber are fermented by the beneficial bacteria and reduce the harmful or pathogenic bacteria that live in our guts. These are called prebiotic fibers. The most well known are inulin, oligofructose, resistant starch, and galactooligosaccharides which are fully fermented.
Not all dietary fibers are fermented by the intestinal bacteria to the same degree – wheat bran and cellulose from plant cell walls are minimally fermented while oat fiber and psyllium may be partially fermented.
What is the difference between probiotics and prebiotics?
Probiotics are beneficial bacteria, while prebiotics are the food that encourage the growth of beneficial bacteria. Very often, people may have good bacteria in their gut, but they are not thriving due to a lack of food (fermentable fiber). If that person starts to eat fermentable fiber, the beneficial bacteria in their gut may be restored to healthy levels.