Recently, articles titled "4 Cooking Habits That May Cause Cancer" have been widely shared on social media. Not cleaning the wok before stir-frying, turning off the range hood immediately after cooking, and reusing oil from deep-frying... These habits, which seem like essential money-saving tips for home cooks, are actually "poisoning" our health and may even lead to cancer. Xia Pengbin, a nutritionist from the Department of Clinical Nutrition at the Affiliated Zhongda Hospital of Southeast University, points out that these four common habits are actually bad ones that one should be cautious of, as they may cause cancer.
Bad Habit 1: Stir-frying in a dirty wok without cleaning it first
This is the first bad habit mentioned in the social media posts and one of the most common lifestyle habits for many lazy people. After scrambling eggs, there's still some oil left in the wok. No problem, just add more oil and continue cooking other dishes. This way, you save both money and oil, killing two birds with one stone. After stir-frying vegetables, there's not much oil left and the wok seems clean, so why not continue using it? However, Xia Pengbin, the nutritionist from the Affiliated Zhongda Hospital, points out that the seemingly clean surface of the wok can have residual oil and food debris. When reheated at high temperatures, it can produce carcinogens like benzopyrene. Moreover, when you stir-fry in a dirty wok, you'll find that the leftover food in the wok burns easily, which also poses a certain cancer risk. Therefore, it is recommended not to skip the step of cleaning the wok. For the sake of your health and the appearance of your food, get that scrubbing done!
Bad Habit 2: Turning off the range hood immediately after cooking
As the dish is about to be done, you turn off the heat, the range hood, and then serve the food—a series of actions completed in one go, marking the completion of the dish. However, this seemingly casual habit hides a "danger." Xia Pengbin explains that some people like to turn off the range hood right after they finish cooking, a habit as natural as turning off the lights. However, this is not good for your health. If the heat is particularly high and the food burns, it can release harmful substances, especially affecting the respiratory system, and may potentially induce lung cancer.
Xia Pengbin further explains that because the cooking process produces a large amount of harmful substances, especially high-temperature cooking fumes, the range hood plays a significant role in exhausting them. In fact, it takes time for the range hood to clear out all the fumes, and some residual fumes may remain in the kitchen after cooking is finished. After cooking, it's a good idea to let the range hood run for another 3-5 minutes to ensure that harmful gases are completely expelled. Additionally, during cooking, try to keep the kitchen door closed and open a window for ventilation, which can also help reduce the residue of harmful substances in the kitchen.
Bad Habit 3: Only adding ingredients to the wok when the oil starts to smoke
How do you know if the oil is hot enough? Many people would answer, "Wait until the oil in the wok starts to smoke." But is this healthy? Xia Pengbin points out that by the time the oil starts to smoke, its temperature is often already over 200°C. Adding ingredients at this point will increase the production of carcinogens and raise the risk of cancer. Under these conditions, many nutrients in the vegetables are also destroyed. Furthermore, at this temperature, not only are the fat-soluble vitamins in the oil destroyed, but also the essential fatty acids for the human body are oxidized and damaged, reducing the nutritional value of the oil. The nutritionist suggests that during the cooking process, it's best to heat the wok first and then add the oil. Trans fatty acids produced by oil at high temperatures are harmful to the human body.
Bad Habit 4: Reusing leftover deep-frying oil for stir-frying
Many people are reluctant to throw away oil used for deep-frying and will use it again for high-temperature stir-frying or more deep-frying. This practice is highly inadvisable. Xia Pengbin believes that reused oil contains residual carcinogens, mainly benzopyrene, as well as some aldehydes and heterocyclic compounds. Cooking oil should ideally be used only once, and at most 2-3 times, while keeping the oil temperature under control. This means you might have to give up eating street-side skewers and stinky tofu!
Regarding the choice of cooking oil, Xia Pengbin explains that from a source perspective, there are mainly animal-based and plant-based oils. In daily life, try to use less animal fat. On the basis of controlling total intake, choose plant-based oils. In the absence of sufficient evidence proving that genetically modified (GM) foods are harmless, non-GM plant oils are recommended. In terms of processing methods, prioritize oils produced by physical pressing, and use fewer oils produced by chemical extraction, as they may contain some harmful chemical residues from the processing. Although these are within safe limits, it's better to consume less of them.
In addition, the nutritionist also gives a special reminder to pay attention to controlling the oil temperature when frying fish, as it is very easy to burn. It's best to add the oil to a hot wok and then add the fish, which will prevent it from sticking. Never wait for the wok to smoke before adding the oil.