You may not have even heard of watercress, but the tiny green that is often used as a garnish or in salads is apparently the healthiest food in the world. According to the CDC, it’s the most nutrient-dense veggie on the planet. It packs more healthy vitamins than any other vegetable, including spinach, parsley and kale. It contains all sorts of antioxidants and amino acids and is great for tissue growth; hormone and neurotransmitter production; and healthy skin, hair, and nails. It also supports the immune system and regular digestion.