Dr. Art, biochemist, is one of those guys (much like Petro “Hyperlipid”) who’s all about the science, all the time, no exceptions. We are fortunate these sorts of single-pupose guys exist; for if not, we’d be in dire need of inventing them…
I am definitely not a bandwagon kind of guy (except maybe in the case of fecal transplants.) So embracing evil, high-glycemic starch as a medicinal godsend was tough. As a biochemist raised on structural analysis of carbohydrates, the idea of starch as a mixture of linear amylose and branched amylopectin, was straightforward. Amylase in saliva and pancreatic solutions digests the linear alpha,1-4, glucan stretches and pullulanase (bacterial) degrades the alpha,1-6, glucan branch points. But this suggests that starch should be digested before it gets to the colon and most of the gut flora. This ignores the spirals of amylose that resist amylase digestion, i.e. resistant starch (RS), and that lead to the puzzling role of RS as a special food for gut flora and a health panacea.
I’ll (I’ll speak for Tim, too, since he’s basking in the sun on The Big Island, presently, and is under order to enjoy it) take a recognition by a guy like Art or Petro for 10 recognitions of anyone else, because I consider them somewhat foundational. I know they are led by their accounting of the science, are able to understand it all, chew it up, and spit it out to us on occasion.
I can’t even hope to completely understand why Art has been persuaded by the science, but I’ll take it anyway.
Why is resistant starch, RS, difficult to digest and terrific for gut flora?
There are several conceptual difficulties to understanding why RS is Real Special:
- Polysaccharides are not all simple linear chains of sugars, e.g. they branch (amylopectin) or form helices (RS, amylose).
- Sugars and polysaccharides have hydrophobic patches. They are amphipathic like soap.
- Amylose (RS) forms a spiral with a hydrophobic surface of each sugar facing inward to make a hydrophobic core and hydrophobic patches on the outer surface that structures water to hold the spirals together. The same principle holds together the double helices of DNA around a central hydrophobic core of stacked base pairs.
- Polysaccharides (soluble fiber) are made of many different sugars, e.g. glucans, mannans, xylans, galacturonans, etc.
- Starch is enzymatically hydrolyzed to glucose, which most gut flora can ferment. Other sugars from other polysaccharides (e.g. pectin, polygalacturonan) must first be converted to glucose for fermentation.
- Soluble fiber polysaccharides made from multiple sugars, e.g. arabinogalactans or xyloglucans, require multiple bacterial enzymes for digestion by gut flora.
- Several hundred bacterial enzymes of the gut flora are required to digest the complex soluble fibers of food plants in a typical diet. Resistant starch requires two.
- Food intolerances (also mistakenly called food allergies) result from missing bacteria and their enzymes to fully digest soluble fibers.
- Novel soluble fibers or sugars are used as laxatives, and they lose their loosening impact as your gut flora adapts to digest the new fiber. Normal, softened stools are half bacteria.
- Amylose spirals are used as a storage form of glucose in seeds, potatoes, roots, etc., because enzymes can’t attack their glycosidic bonds to hydrolyze the starch into amylodextrins and glucose.
- Bacteria digest amylose by attaching the spirals to their cell walls and using wall-bound enzymes to tear the amylose apart. It’s like the different requirements of a wood chipper (pancreatic amylase) versus a man with a chain saw (bacterial amylase).
- The spirals of RS melt during cooking and become susceptible to gut amylase. Melted amylose can sometimes slowly reform enzyme-resistant spirals, RS, when chilled. Al dente or chilled pasta has more RS and raises blood sugar less than soft pasta.
Poor Richard. Poor Animal. There’s more. Any biochemists out there care to do a layman’s translation? I got that it’s cool. 🙂