Hi goodphyte and welcome!
Early on I tried soaking carrots to remove the starch (like you do with fries). But starch is only released from the cut surface, not the inside, so while it might help with carrots (which are fairly low starch to begin with) it probably won't do much for potatoes, parsnips or sweet potatoes. They'll still be too starchy to eat.
Fortunately, there are some very low starch root vegetables: rutabaga, celery root, beets and carrots. Roasted rutabaga "fries" are a winter staple and mashed rutabaga and celery root makes a superior topping for shepherd's pie.
Keep in mind that starch content varies, so I test with iodine. Starch varies because frost turns some of the starches to sugar. Problem is, there's no way to know the harvest date. So this year I went the extra mile and grew my own root veg to harvest after frost (some of them are still in the ground even now!)
As for having a hard time getting a diagnosis, that's a common story here. When my test results came back negative (which is not uncommon) my rheumatologist actually dismissed me with mindfulness pamphlets. Fortunately, by that time I had found this forum and the NSD and I've never looked back.
Diagnosis was only important to me as a path to a (natural) solution so I just gave up. I was never going to take their drugs anyways because of the side effects and risks, and they have nothing else to offer.
And it hasn't been necessary anyways, because NSD has done wonders. My joints not only stopped getting worse, they've improved. But that's just me...you'll have to decide for yourself.
Suspected USpA. HLA B27, xray, u/sound, blood tests all -ve. Ancient history of plantar fasciitis, SI joint pain, knee arthritis. Recent history of tendinitis, neck pain, debilitating finger pain and stiffness (especially mornings). No diagnosis, no meds.
2010 - stopped eating dairy
2012 - stopped eating wheat
2014 - stopped eating all grains
Jan 2017 - discovered NSD - 98% improvement in symptoms, continually amazed by my results, wish I'd found kickAS sooner