After bariatric weight loss surgery it is common to have high urine oxalate and low urine citrate -factors that lead to kidney stone formation .So you need to be extra careful regarding your intake of water and food. Increase your water and fluid intake. Eat low fat diet as the amount of oxalate in the urine increases with the amount of fat in the stool after bypass surgeries. Limit the intake of foods rich in oxalate like chocolate, cocoa, spinach and other dark green leafy items, nuts, soy products, most berries, beets, beans, and tea. Avoid excess of vitamin C in your diet as it can convert into oxalate. With all these precautions and appropriate medical help you will definitely have lesser chances of recurrent oxalate stones. Hope it helps.