Spinach

Spinach is loaded with oxalates—natural plant chemicals that bind to calcium in your body. When too many oxalates meet calcium, they form sharp crystals called calcium-oxalate kidney stones. Spinach has around 1,000–1,200 mg of oxalates per 100 g, one of the highest levels among any food. If you’re already at risk for stones or have had them before, that’s a dangerous combo.