For the person with chronic kidney disease apples are okay, but bananas are not. They have too much potassium. If the kidneys are not working properly they are unable to regulate the amount of potassium the body needs. Too much potassium in the blood can cause heart irregularities.
New research indicates that eating and drinking calcium and oxalate-rich foods together during a meal is a better approach than limiting oxalate entirely because oxalate and calcium are more likely to bind to one another in the stomach and intestines before the kidneys begin processing, making it less likely that kidney stones will form.