Q: After reading "Chinese People Lack Leafy Greens" from issue 188 of the Life Times, I found it very enlightening. However, I saw an article the other day that said vegetables only have nutritional value when eaten raw. Is this true? I have elderly family members at home, and they tend to get diarrhea from eating raw vegetables. What should I do? —Ms. Zhao, a reader from Beijing
Associate Professor Fan Zhihong from the College of Food Science, China Agricultural University: For many years, people have repeatedly emphasized that eating raw vegetables is beneficial to health. The reason is easy to understand: eating raw vegetables does not lead to the loss of nutrients and can best preserve the active substances in them. However, is cooking vegetables completely inadvisable? In fact, as long as the cooking is reasonable, eating cooked vegetables also has its benefits. It may not be as bad as some people imagine, with nutrients being completely wiped out, and there are even some "extra" benefits:
1. Cooking can increase the utilization of vitamin K and carotenoids in green leafy and orange-yellow vegetables. These two types of substances are only soluble in oil, and heat cooking softens the cell walls, promoting the dissolution of carotene and lycopene and increasing the absorption rate.
2. Cooking can increase the utilization of calcium and magnesium elements in vegetables. Many people only know that calcium comes from milk and magnesium from bananas, but they don't realize that green leafy vegetables are also good sources of these nutrients. This is because most green leafy vegetables contain oxalic acid, which is not conducive to the absorption of calcium and magnesium. However, during the cooking process, as long as they are blanched, and then stir-fried or served cold, most of the oxalic acid can be removed.
3. Cooking can significantly increase the amount of vegetables consumed. Although raw vegetables lose no nutrients, it is difficult to increase the total amount consumed. People all have this experience: if you are required to eat 500 grams of vegetables a day, it is very difficult to meet this requirement by eating them all raw. If half of the vegetables are cooked, then meeting this requirement becomes easy.
4. Cooking can soften fibers, which is beneficial for people with weak stomachs, indigestion, bloating, or chronic diarrhea.
5. Finally, cooked vegetables are more hygienic. Heating can kill bacteria and insect eggs, and even E. coli O157 has difficulty surviving the baptism of boiling water or hot oil. Some anti-nutritional factors and oxidative enzymes that destroy vitamins can also be inactivated during the heating process.
The ideal approach is to cook most of the darker-colored vegetables and eat the lighter-colored and crisp-tender vegetables raw. The cooking temperature for vegetables should be kept as low as possible, and the cooking methods should be light and low in oil. In this way, both quantity and quality, nutrition and taste can be balanced.