I don't know if this is relevant, but the title of this thread reminds me of the claims for unmodified potato starch. There's a lot on the www that explains it better than I can, but this is a type of starch that's called "resistant" starch because we can't digest it. But it's supposed to be superfood for a type of bacteria that makes something that's a precursor to seratonin. Many people, including me, report hugely improved sleep very quickly with it. I mix a couple Tbs with h2o every night, sometimes alone or with some tart cherry concentrate, or some turmeric (for curcumin) or whatever.
Supposedly, cooking potatoes turns the resistant starch into digestible starch, so you don't get the same benefits from cooked potatoes. Raw potatoes are pretty much inedible, but you buy the stuff in a bag at the grocery store- Bob's Red Mill has reasonably priced- has to be the 'unmodified,' though. Some studies show after cooked potatoes are cooled, some of the starch turns back into a type of resistant starch, so potato salad might good for that.