Green beans, while quite low in calories (just 43.75 calories in a whole cup), are loaded with enough nutrients to not only power up the Jolly Green Giant, but to put a big smile on his face. Green beans are an excellent source of vitamin C, vitamin K and manganese. Plus green beans are very good source of vitamin A (notably through their concentration of carotenoids including beta-carotene), dietary fiber, potassium, folate, and iron. And, green beans are a good source of magnesium, thiamin, riboflavin, copper, calcium, phosphorus, protein, omega-3 fatty acids and niacin.