string beanscontain pigments that give vegetables their red, yellow and orange colors, called carotenoids, all function as antioxidants. String beans contain three carotenoids: beta-carotene, lutein and zeaxanthin. Beta-carotene is converted into retinol, which is the form of vitamin A essential for normal night vision. Lutein and zeaxanthin absorb blue light, which protects your eyes from damage caused by this high-intensity light. String beans are low in sodium, very low in saturated fat and cholesterol + a good source of protein, thiamin, riboflavin, niacin, vitamin B6, calcium, iron, magnesium, phosphorus, potassium and copper, and a very good source of dietary fiber, vitamin C, folate and manganese.