At a Glance Citrus fruits are known for being high in immune - supporting vitamin C, but they also contain other nutrients that support overall health. Oranges, grapefruits, lemons, mandarins, pomelos, and kumquats are among the m ost nutrient - dense citrus fruits. Look for citrus fruits that feel firm and smooth, with no soft spots or bruises. The healthiest citrus fruits offer zesty flavor and a range of nutrients. You'll find fiber, antioxidants, vitamins, and minerals in these co lorful fruits, which support heart, skin, and immune health.