This stuff here, Shirakiku yam noodle, is the perfect substitute for spaghetti or ramen noodles when you are looking for a zero-calorie and near zero-carb experience. I found these at New Sagaya, a local market that carries Japanese products along with other Asian specialties. My favorite joint, Red Apple, doesn't carry Japanese brands such as Shirakiku, so you might need to look around a bit.
Anyhow, here is the low-down on yam noodle. They stink. Of course they won't mention that on the bag, but trust me, they smell unappealing. So here is the trick: Before using them, open the package up into a colander, and rinse them under cold water for a minute or so to get most of the smell of them.
For chicken soup or ramen, I toss 'em into whatever I'm cooking up so they boil along in there for three minutes or so. They work pretty well like that. As for spaghetti, well, I think I'd boil the noodles in the spaghetti sauce for a few minutes. But yam noodle, yeah. You'll like 'em if you can find 'em.