Spinach may not be as healthy as you think. It's extremely high in oxalates—1,510 mg per cup cooked—which can contribute to kidney stones and conditions like vulvodynia in women. Oxalates bind with calcium, forming harmful crystals. To reduce risk, avoid high-oxalate greens like spinach and choose low-oxalate options like romaine, arugula, and cabbage instead. Talk to your doctor if you have symptoms or kidney stone history.