I do have some additional information for you. Raw starches are all RS2. Plants use starch to store energy and pack it into tight granules. The granular structure is what resists digestion, not the chemical composition of the amylose/amylopectin ratio contained within that granule. All raw starches are high in resistant starch. For instance, green bananas are extraordinarily high in resistant starch as long as they are raw – they are also very high in amylopectin. Different raw starches contain different quantity of resistant starch because the drying process can destroy part or all of the resistant starch if it is not carefully controlled.

The amylose content is important in the gelatinization temperature of the starch. Higher amylose content takes more energy to cook out, destroying the granule structure. Thus, high amylose corn and high amylose wheat will retain its granular resistant starch after baking, while green bananas and potato starch will turn into rapidly digestible starch after baking. Baked high amylose corn resistant starch is not RS3 – it is still RS2 because it retains the granular structure. You can see it under a microscope. Also, Hi-maize is not chemically modified RS4 – it has not been chemically treated to introduce indigestible bonds – its resistance is based upon retaining the granules produced by the plant. It was produced by traditional breeding methods over many years and is not genetically engineered. The high amylose content has textural properties in the food industry so it was grown for this purpose. (For instance, high amylose cornstarch is used to make jelly beans, but the process blows apart the starch granule and all of the RS is destroyed.). The discovery that it was also a dietary fiber/resistant starch was discovered later.

I think you meant to say that resistant starch has a lower glycemic response. All types of dietary fiber have a lower glycemic response when compared to the same quantity of rapidly digestible carbs. Typically, processed carbohydrates are all high glycemic and rapidly digestible (including refined whole grain bread and oatmeal). Glycemic Index is different and refers to a very specific analytical procedure. Hi-maize does not have a lower Glycemic Index but this is because of the test procedure, not the food. I’ve been arguing against Glycemic Index for more than a decade for this reason.

Your information on supplemental sources of resistant starch is strange and misleading. Starch that has been extracted and highly processed is usually submitted to extreme processing, which destroys the resistant starch that was naturally present in the original plant. The best supplemental sources of resistant starch are green banana, Hi-maize high amylose corn, and raw potatoes right now. There has been an RS3 from tapioca used in European research but I have not seen it in the US. NuBana brand green banana resistant starch has a consistent high quality – averaging 65% resistant starch, but it must be consumed raw. It’s nothing more than dried green bananas (really really really green banana – much greener than you can get in a grocery store). Other sources of green banana flour usually test at around 40% resistant starch. Hi-maize contains 50-55% resistant starch and as you noted, is extracted and isolated. It has been used in most of the research because it has been available for so long and has had long-term advocates in the research community. Raw potato resistant starch can be as high as 70% resistant starch (MSPrebiotic brand), or as low as 30% resistant starch depending on how it is processed and if it is extracted or not.

I hope this information helps. Thanks again for a great article. If