Introduction: When cooking, people's biggest concern regarding nutrient loss is with vegetables. Vegetables can be stir-fried, boiled, steamed, or served cold... Which method is most effective for preserving nutrients, encouraging higher vegetable consumption, and preventing various diseases?
Stir-frying
Heat oil, briefly stir-fry to release aroma, add vegetables and stir-fry until done, then serve immediately. The advantage is that it works for almost all vegetables, the volume shrinks significantly, making it easier to consume the recommended daily amount of 500g of vegetables, and the nutrient loss rate is relatively low. The disadvantage is that it requires more oil for better taste, which is unhealthy for you. If the oil temperature is not controlled during cooking, overheated oil can produce carcinogens.
Stewing
Heat oil, briefly stir-fry to release aroma, add vegetables, stir-fry, then add a small amount of water and cover the pot to stew the vegetables until tender. The advantage is that the vegetables absorb flavor well, have a soft texture, and their volume shrinks, making them suitable for large consumption. The disadvantages are that it can only be used for sturdy, slow-cooking vegetables like potatoes, carrots, radishes, beans, and winter melon; the nutrient loss rate is relatively high; it produces smoke; and it uses a relatively large amount of oil.
Steaming
Steam vegetables directly, or first toss them with rice flour, corn flour, wheat flour, or soybean flour before steaming. The steaming time varies from 3 to 30 minutes depending on the vegetable's texture. The advantages are no smoke, the least nutrient loss, the volume shrinks after cooking making it suitable for large consumption, and it requires very little oil—just a little sesame oil or sesame paste in the seasoning sauce is enough. The only drawback is that you need to know the optimal steaming time for each vegetable; for example, leafy greens must be taken out within three to five minutes and should never be steamed for too long, or the texture will be poor.
Blanching
Place vegetables directly into boiling water and remove them after 30 seconds to two or three minutes, depending on the vegetable's texture, quantity, and heat intensity. Spread them on a plate to cool, then eat with your favorite seasoning sauce—whether it's minced garlic with sesame oil, sesame paste sauce, fermented bean curd sauce, or chili sauce. The advantages are no smoke, the volume shrinks making them suitable for consumption, less oil, and it removes more than half of the organophosphate pesticides and oxalic acid. The disadvantages are that more than half of the soluble nutrients (including vitamin C, folic acid, vitamin B2, flavonoids, and anti-cancer compounds like glucosinolates) dissolve into the water. Additionally, the vegetables' color becomes darker after cooking, and if the leaves are old, they can be difficult to chew.
Scalding
Scalding is similar to blanching, but the restaurant method involves adding a small amount of oil and salt to the water first to keep the vegetables' color bright and glossy. The difference from blanching is that it requires a separate pan to heat oil and light soy sauce or other sauces, which are then poured over the blanched vegetables, as in the case of "scalded kale" or "scalded bok choy."
The nutrient loss rate for scalding is the same as for blanching: a large loss of soluble nutrients but a high retention of insoluble nutrients. As for the amount of oil consumed, it depends on how much oil is in the final seasoning sauce.
Boiling in Oil
(including using various meat or chicken broths): First, bring a small bowl of water (200-250g) to a boil, add a teaspoon of sesame oil (8g), then add leafy green vegetables (300g) and cook for two to three minutes. There isn't much water, not enough to cover the vegetables, but since the vegetables only need to be turned a couple of times to cook and release their own water, very little water is needed. After cooking, simply add seasonings to your liking. The advantages are that adding salt at the end of cooking reduces nutrient loss; since you drink all the broth, no nutrients dissolved in it are wasted, with only minor losses from heating. As long as the cooking time is not too long, the nutrient loss rate is lower than with blanching. Compared to oil-free blanching, adding a small amount of oil or using broth makes the vegetables more tender in texture, brighter in color, and easier for the elderly and children with poor dentition to accept. Compared to stir-frying, this method produces no carcinogens and saves oil. Because you only need one teaspoon of oil to cook a large pot of vegetables, whereas one teaspoon of oil is not enough to make a tasty stir-fried dish. Therefore, this method is highly recommended.
Eating Raw
Wash vegetables and eat them directly with your own mixed seasonings or salad dressing. The advantage is that it's simple and easy, and there is no loss of nutrients or health-promoting compounds. The disadvantages are that the volume of the vegetables does not shrink, making it difficult to achieve the goal of eating 500g of vegetables a day. In terms of oil consumption, a small amount of salad dressing (with 40%-80% fat content) or sesame oil, pepper oil, chili oil, etc., is needed for a small amount of vegetables. It should be noted that compared to the cooking methods mentioned above, eating raw has the lowest safety profile, with a greater risk of bacterial food poisoning, and some sensitive individuals may experience gastrointestinal discomfort.