Generally, vegetables can be divided into three main categories: leafy-stem, root, and fruit types. Additionally, there are flower and gourd vegetables.
Leafy-Stem Vegetables
Examples include rape, chives, bok choy, and spinach. They are rich in vitamin C and carotene. Spinach contains iron, but it also has oxalic acid, which can hinder the absorption of calcium and iron from food. Therefore, it should be briefly blanched in boiling water before cooking.
Root Vegetables
Examples include radishes, carrots, taro, potatoes, and sweet potatoes. Radishes are very high in vitamin C, carrots contain a large amount of carotene, and potatoes and taro are high in starch and calories but have fewer other nutrients. A common characteristic of root vegetables is their rich content of dietary fiber. If radishes or carrots are sliced thinly or into strips and left for 1-2 days, their dietary fiber content can increase by about 3 times. Therefore, radish-based foods should be cut and eaten immediately, not stored after cutting.
Fruit Vegetables
Examples include tomatoes, beans, bell peppers, cucumbers, loofah, pumpkin, and eggplant. With the exception of beans, pumpkin, loofah, and eggplant, it is best to eat these vegetables raw to avoid the destruction of vitamins during cooking. Tomatoes contain a good amount of lycopene and vitamin C. Beans, including lentils, peas, and edamame, have a high protein content, with a more complete amino acid profile than grains. They also contain higher levels of calcium, phosphorus, iron, and vitamin B1 compared to other vegetables. Pumpkin is very rich in carotene, and peppers are abundant in both carotene and vitamin C.
Nutritional content also varies among different parts of the same vegetable. For example, the green part of a green onion has a much higher nutrient content than the white part. The white part contains less than half the amount of vitamin A, vitamin B1, and vitamin C found in the green part. In celery, the dark green leaves contain more vitamins A and C than the pale green stalks. The same is true for bok choy, where the leaves are more nutritious than the stems.
Since the human body requires a "full spectrum" of nutrients, it is impossible to meet this requirement by eating only one type of vegetable. Therefore, only by reasonably and cleverly combining a variety of vegetables with different colors can we ensure a balanced nutritional intake.