One of the best substitutions for a white potato is cauliflower. A serving of the cruciferious veggie contains under 30 calories and 5 carbs! By using cauliflower in dishes like mashed "potatoes" -- you dump a huge amount of carbohydrates -- which is beneficial for a bariatric surgery patient as we are typically restricting our intake of the blood sugar spikers.
And, cauliflower tastes really, really good, when you put stuff on and around it. <g>