Swiss chard, also known as leaf beet, is a leafy green vegetable that belongs to the same family as beets. Its leaves have a mild flavor like spinach, but it has a slightly tougher texture that softens when you cook it. Swiss chard is a rich source of vitamin K, although it contains less vitamin C than the top two most nutrient-dense veggies, watercress, and Chinese cabbage, per calorie.

One downside is Swiss chard is high in oxalates. If you have a history of calcium oxalate kidney stones, it’s best to avoid Swiss chard since it can increase the amount of oxalates in your urine and boost the odds of kidney stones forming. Cooking Swiss chard reduces but doesn’t eliminate, oxalates.