Soybeans can be classified into five types based on their color: yellow, green, black, brown, and bi-colored. Among these, yellow soybeans are the most representative, and when people refer to soybeans in general, they are usually talking about yellow soybeans. The nutritional value of soybeans is distinctive:
1. They have a high protein content, which is of better quality than protein found in grains and is similar to the protein in meat. The protein content of yellow soybeans is about 40% (lean pork contains 16.4%, eggs contain 14.7%, and milk contains 3.3%). Other legumes like broad beans, peas, mung beans, and red beans also have a higher protein content than grains, reaching 20% to 30% (compared to about 10% for grains). The amino acid composition of legume protein is close to the human body's needs, with a proportion similar to animal protein. Lysine, which is relatively lacking in grains, is abundant in legumes. Therefore, it is advisable to consume them with grains to improve the biological value of protein in the diet.
2. Soybeans have a relatively high fat content, ranging from 15% to 20%, with yellow and black soybeans having the highest content and often used as raw materials for edible oils. Soybean oil is one of the most commonly used cooking oils. The fat in legumes is predominantly composed of unsaturated fatty acids. Taking soybeans as an example, their fat composition is: palmitic acid 2.4%-6.8%, stearic acid 4.4%-7.3%, arachidic acid 0.4%-1.0%, oleic acid 32%-35.6%, linoleic acid 51.7%-57.0%, and linolenic acid 2.0%-10.0%, with unsaturated fatty acids accounting for over 86.1%. Additionally, legumes contain about 1.64% phospholipids. Consequently, soybeans and soybean oil are often recommended as ideal foods for preventing and treating coronary heart disease, hypertension, atherosclerosis, and other diseases.
3. Zero cholesterol. As a plant, soybeans contain no cholesterol. Soybeans are the only food that is high in valuable protein and has very little (or even zero) cholesterol. This is one of the reasons why soy protein is healthier than meat protein.
4. Soybeans are rich in calcium. Furthermore, due to the coagulants added during processing, the calcium content in soy products is remarkably high. The calcium in 250 grams of tofu is equivalent to that in 250 milliliters of milk. If milk and dairy products are the first choice for dietary calcium, then soy products are undoubtedly the second.
5. Soybeans also contain B vitamins, especially a relatively high amount of vitamin B2.
6. Soybeans are also rich in elements such as phosphorus, sodium, and potassium, making them a good source of minerals.
7. Of course, soybeans also contain some components that are unfavorable for digestion and absorption or have a beany flavor, including oligosaccharides that cause intestinal bloating, antitrypsin factors that interfere with protein digestion and utilization, saponins and phytates that affect the absorption of trace elements, and goitrogens that may be detrimental to the thyroid.