Spinach

Doctors have seen patients end up in the ER after drinking daily green smoothies loaded with spinach and kale. Even healthy people can trigger stones if they’re dehydrated or lack enough dietary calcium to balance the oxalates. Nutrition experts suggest variety—mix greens, drink plenty of water, and avoid going overboard on spinach if you’ve ever had kidney stones. Sometimes, too much of a “superfood” really isn’t super at all.