Oxalate combines with calcium to form insoluble crystals that make up the majority of kidney stones (calcium oxalate). There are many foods that contain large amounts of oxalate. Lists are available on the internet or in dietary publications. Eight foods have been associated with significant elevations in urine oxalate levels (beets, chocolate, nuts, rhubarb, spinach, strawberries, tea, wheat bran).
Your health care provider may recommend decreasing your intake of certain foods rather than complete avoidance/elimination.