Green beans are low in calories and fat, but high in water and fiber. A cup of green beans has only 31 calories, 0.2 grams of fat, 4 grams of starch, 2.7 grams of fiber, 1.8 grams of protein, and 0.1 grams of sugar. Green beans also provide you with minerals, such as potassium, calcium, magnesium, iron, zinc, and selenium; vitamins, such as vitamins A, C, K, B1, B2, B3, B6, and folate; and antioxidants, such as chlorophyll, flavonoids, lignans, phenolic acids, carotenoids, and polyamines.