Vegetables are high in water and low in energy, rich in phytochemicals, and are an important source of micronutrients, dietary fiber, and natural antioxidants. Fresh vegetables generally contain 65%-95% water, with most having a water content of over 90%. Vegetables contain cellulose, hemicellulose, pectin, starch, oligosaccharides, and most have low energy (50 kcal/100g), making them a type of low-calorie food.
At the same time, each category of vegetables has its own nutritional characteristics. Young stem, leaf, and flower vegetables such as cabbage, spinach, and broccoli are good sources of carotene, vitamin B2, vitamin C, folic acid, calcium, phosphorus, potassium, and iron. Among these, vitamin C is abundant in the metabolically active leaves, flowers, and stems of vegetables, parallel to the distribution of chlorophyll.
Generally, dark-colored vegetables have higher levels of carotene, riboflavin, and vitamin C than light-colored vegetables, and they contain more phytochemicals. In the same vegetable, the vitamin content in the leaves is generally higher than in the roots and stems; for example, the vitamin content in lettuce leaves, celery leaves, and radish greens is several times higher than in their corresponding roots and stems. Common vegetables are divided into the following categories:
Leafy vegetables: The nutritional value of leafy vegetables is generally higher than that of gourds.
Root vegetables: Root vegetables, mainly radishes, carrots, and turnips, contain less dietary fiber than leafy vegetables.
Cruciferous vegetables: Cruciferous vegetables such as radishes, broccoli, kale, cabbage, Brussels sprouts, and cauliflower contain phytochemicals like aromatic isothiocyanates, which are the main components present in the form of glycosides.
Aquatic vegetables: Among aquatic vegetables such as water chestnuts, lotus root, wild rice stem, arrowhead, watercress, and water celery, water chestnuts and lotus root have a higher carbohydrate content.
Fungi and algae vegetables: Fungi and algae vegetables such as button mushrooms, shiitake mushrooms, wood ear fungus, yeast, nori, and kelp contain protein, polysaccharides, carotene, and minerals such as iron, zinc, and selenium. Marine fungi and algae like nori and kelp are also rich in iodine.
Tuber and tuberous vegetables: Tuber and tuberous vegetables such as sweet potatoes, potatoes, Chinese yams, and taro are mostly rich in starch and oligosaccharides, have higher energy, and should be counted as staple foods when consumed.