Of all my low carb substitutes for the "bulk" part of meals; potatoes, rice pasta etc. swede has been the most successful. Make swede mash instead of potato mash, cut swede into 2cm cubes and boil in salted water for about 30 mins until soft (ish) drain well, mash with plenty of butter and black pepper. Delicious with just a hint of my nemesis the cornish pasty. Or cut into thin chips, drizzle with olive oil, dust with paprika or cumin or just salt and pepper and roast in a single layer at about 190deg for 40mins until starting to get a bit burnt. Not as crisp as potato chips but very tasty.