Some green beans can't be cooked because they are mostly wild green beans or varieties of green beans, known as "iron beans". Although on the surface and ordinary green beans look no different, but their pulp is very hard, need to soak for about 12 hours to cook.

Each 100 grams of green beans contains 23.8 grams of protein, 58.8 grams of carbohydrates, 0.5 grams of fat, 80 milligrams of calcium, 360 milligrams of phosphorus and 6.8 milligrams of iron. It also contains carotene, vitamin B1, vitamin B2, vitamin E, niacin and various mineral elements. The protein contained in mung beans is mainly globulin and contains amino acids such as methionine, tryptophan and tyrosine. The phospholipids contained include phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylglycerol, phosphatidylserine and other components.