Thanks for bringing this study to my attention. There’s so much info on this subject, it’s difficult to fully cover it here, but here are a few thoughts.
The finding that jasmine rice (and short grain rice) has little resistant starch, even after refrigeration is consistent with the assignment of a high GI and low FP for this rice variety. Recall in the book, we warn that refrigeration or starches can increase the amount of RS. Better to eat it fresh.
It’s a little hard to assess their finding of relatively low levels of RS in the long grain rice they tested as I don’t know the details of the rice variety and brand they used. It would have been interesting if they included the high FP varieties (for instance, basmati and Uncle Bens) that I list in Fast Tract Digestion. I would like to see what GIs values they would get with those rices and would expect them to be low as previously reported.
As for the finding that freshly cooked jasmine rice has more RS than medium or short grain rice, the reason likely lies in how RS is analyzed in the test tube by invitro enzyme-based methods such as the preferred method, AOAC 2002.02. The test involves extensive enzymatic digestion of the starch for many hours. Perhaps that is the reason even high amylose-starches yield relatively low levels of RS by this assay. But many studies have linked high amylose starches (specific varieties of corn, potato, rice, etc) to low GIs and low amylose starches (including both short grain and jasmine rices) to high GIs. Based on this body of work, I feel pretty confident calculating high and low FP values from these low and high GIs.
In other words, amylose, the more resistant starch, can still be digested, just not as easily or quickly as amylopectin starch. That’s the reason in my opinion that the GIs are lower (and FPs higher) for high amylose starches. Because they don’t digest as fast thus creating fermentation potential (the reason I call it “potential” is because it’s not an absolute) that can overfeed gut bacteria, particularly in the small intestine.