■ Smell and sing
Statistics show that false news spreads 6 times faster than real news, and its forwarding probability is 70% higher than real news. With the continuous improvement of modern living standards, people’s attention to diet health is also increasing. However, in recent years, false rumors about health preservation, diet nutrition and other aspects have frequently appeared in various forms. These specious false information deviates from science and is far from the truth, confusing and misleading people’s cognition for a long time, and even causing health harm to many people.
As the saying goes: it’s really not fake. Let’s listen to how medical and nutrition experts use scientific methods to analyze these dietary rumors and nutritional misunderstandings, smash rumors with knowledge, make the truth more and more clear, and lead us to practice healthy life with a scientific attitude.
Nutrition myth 1: Can eating more beans and their products lead to precocious puberty?
In recent years, there is a rumor that frequently bothers women, that is, soybean isoflavones contained in soybeans are phytoestrogens. Eating more soybeans and their products will promote children’s precocious puberty, and women will also induce breast cancer. The reason is that since it is a hormone, eating more will definitely lead to excessive intake of hormones, which will adversely affect women and children.
Experts dispel doubts: Chen Yiying, deputy director of Jiangxi CDC, pointed out that soybean is rich in high-quality plant protein, and soybean isoflavone contained in it is a polyphenol compound. Because its chemical structure is similar to estradiol, it can play the role of estrogen-like and regulate endogenous estrogen, so it is called phytoestrogen.
However, Chen Yiying reminded that soybean isoflavones ≠ Estrogen. Soybean isoflavones show estrogen effect when the estrogen level in the body is low; However, when the estrogen level in the body is high, it shows anti-estrogen effect and can regulate the estrogen level in the body. Clinical experiments show that soybean isoflavone intake has no effect on the level of sex hormones in perimenopausal and postmenopausal women, and has no obvious effect on the level of sex hormones in men. Therefore, soybean isoflavone is not a hormone, but only plays a role in regulating estrogen, so the nutrition community has always advised women to eat more soybeans and their products.
So how much soybean and its products can be considered excessive? According to the monitoring results from 2010 to 2013, the maximum consumption of this kind of food (converted into soybean) by Chinese residents at different ages did not exceed 10 grams for women and 10 grams for children at different ages. However, the recommended consumption of beans and their products in China’s dietary guidelines is 17-25g, which is far from the recommended consumption of Chinese residents, and there is still room for more daily consumption. The maximum tolerable intake of soybean isoflavones for postmenopausal women in China is 120mg per day, which means that 155 grams of soybean &asymp should be eaten every day. 2260 grams of soybean milk ≈ 340 grams of dried bean curd ≈ 450 grams of north tofu ≈ 868 Kenan Tofu ≈ 248 grams of shredded tofu ≈ 326 grams of vegetarian chicken; For men and premenopausal women, the upper limit of their intake has not yet been set.
Nutrition myth 2: Can extra virgin olive oil only be cold and not stir-fried?
In the 2021 US News and World Report Diet List, the "Mediterranean Diet" was ranked first, and olive oil was the main source of fat in this diet. Extra virgin olive oil contains high monounsaturated fatty acids and bioactive substances such as polyphenols, which has certain antioxidant and anti-inflammatory effects and can prevent cardiovascular diseases. However, many people believe the rumor that "olive oil can only be cold but not fried", thinking that the beneficial substances in olive oil will be destroyed and even produce harmful substances after heating, and thus think that olive oil is not suitable for Chinese food.
Experts’ explanation: Zheng Xixi, a clinician of Peking Union Medical College Hospital, pointed out that in the process of high-temperature cooking, the fat in oil will be oxidized, the long chain of fatty acids will break, and trans fat will be produced, but this is related to the cooking method and the "smoking point" of oil. If the heating temperature is higher than the smoking point, some unfavorable chemicals may be produced. The smoke point of extra virgin olive oil is 190~200℃, which is about 20℃ lower than refined peanut oil, soybean oil and sunflower oil commonly used in life, but higher than some unrefined peanut oil and soybean oil.
Some researchers compared the composition changes of different vegetable oils after "Chinese-style" cooking methods, and found that among many vegetable oils, the monounsaturated fatty acids in olive oil were destroyed the least in various cooking methods, and the antioxidant capacity was the strongest. The study also found that after frying and frying with olive oil, the contents of fat and polyphenols in food increased, but decreased after cooking. This shows that extra virgin olive oil can be used for cooking, but like all other oils, the cooking time should not be too long and the oil temperature should not be too high. In fact, the oil used in "Mediterranean diet" for cooking, frying fish, making soup and making traditional pasta sauce is also olive oil.
It should be noted that olive oil is also good or bad. What is written on the ingredient list is not "extra virgin", but olive oil that is chemically extracted and extra virgin. From extra virgin olive oil — Virgin olive oil — Olive oil — Olive residue, with the decline of olive oil grade, its health benefits also shrink.
Nutrition myth 3: Can you really lose weight and live longer without dinner?
The method of "not eating dinner" has been recognized by many dieters, and it is also called the "golden rule" of losing weight. Some people even say that skipping dinner can prevent diseases and prolong life.
Experts dispel doubts: Peng Yigu, a food science researcher, believes that human body weight is not only controlled by fat, but also a large part of water, and most of what is lost without dinner is water.
For an adult male, it takes 2250kcal of energy every day to maintain his "livelihood", which is about 1 kg after being calculated into weight. If you don’t eat anything all day, you can lose about a catty. If you just skip dinner, you will lose about 150g g. But the human body is metabolizing energy all the time, that is, converting energy into energy. If you don’t eat dinner, you will be in a state of no energy supply for about 10 hours before breakfast the next day, but the energy consumption has not stopped. Without supply, the body will decompose protein. Protein is a component of muscle, and when protein is consumed, the muscle is reduced. There is a trade-off between muscle rate and fat rate. With less muscle, there will be more fat, and the amount of glycogen stored will decrease, so when there is excess energy, it will be easier to store it as fat. Therefore, not eating dinner for a long time may be fatter than before, and it is particularly easy to regain weight.
There are more studies to prove that if a person does not eat dinner for a long time, it is easy to get gastritis, and in severe cases, it may induce gastric cancer. In addition, endocrine disorders will also come to your door. The most common thing is that acne will continue to grow on your face, your skin will turn yellow, and your mood will change. Women are also vulnerable to gynecological diseases. If a person suffers from chronic diseases and doesn’t eat dinner for a long time, it is likely to further worsen his condition, not to mention live a long life.
Nutrition myth 4: Is eating frozen meat harmful to health?
In life, almost every family eats frozen meat because it is convenient to store. However, an argument that eating frozen meat is harmful to health also pops up from time to time to interfere with people’s audio-visual, especially after the epidemic in COVID-19, whether cold chain food is safe or not has attracted many people’s attention.
Experts dispel doubts: frozen meat is included in the local meat reserve system in China, and the production and preservation of frozen meat are very strict. After slaughter, livestock and poultry meat is quickly frozen below -25℃ and stored at -18℃, and the deep temperature of meat must be kept below -6℃. At this temperature, spoilage bacteria are basically inactive and will not multiply, so eating frozen meat will not cause harm to the body. According to food safety experts, in this ideal state, the shelf life of livestock meat such as pork, beef and mutton can reach 2 years, that of poultry meat such as chicken and duck can reach 1 year, and that of fish and seafood products can reach 6 months.
Wang Guoyi, a postdoctoral fellow in nutrition and food safety at China Agricultural University, believes that the storage time of frozen meat is not only related to the storage temperature, but also related to the variety of meat and the freshness of meat before freezing. Although frozen meat has a long shelf life in theory, meat bought from supermarkets is easily contaminated by bacteria in the sales process; In addition, the frequent opening and closing of household refrigerator doors and sudden power failure will make the refrigerator temperature fluctuate, which will accelerate the oxidative decomposition of nutrients such as fat, protein and vitamins, and the bacteria will grow slowly, which will reduce the nutritional value of meat and make the taste and flavor worse. Therefore, all kinds of meat purchased from supermarkets should be eaten within one month after freezing, and it is best to eat and buy it now. The shorter the storage time in the refrigerator, the higher the nutritional value of meat, the better the flavor and taste, and the higher the food safety.
Nutrition Myth 5: Is vinegar at the beginning of edible product label "SB" harmful?
In recent years, it has been circulated on the Internet that the letters "SB" are printed on vinegar bottles, which means that vinegar is prepared, that is, "blended vinegar". People who eat it for a long time will affect their health, and it is not recommended to buy it even if it is cheap. So what is the preparation of vinegar? Is it really harmful to health?
Experts’ explanation: According to the mode of production, vinegar can be divided into two categories: fermented vinegar and prepared vinegar. The former uses grain as the main material and is obtained by fermentation; The latter is made of glacial acetic acid or brewed vinegar and other auxiliary materials. Both of them are legal production methods, but the product standards and flavors are different. While "SB" refers to the product standard code name. In China, the vinegar starting with "SB" is "preparation vinegar", and the vinegar starting with "GB" is fermented vinegar.
Experts pointed out that all vinegar sold through formal channels is a qualified product, and it will be clearly marked whether it is brewed or prepared. As long as the quality is qualified at the time of purchase, it can be safely eaten. It is an "ugly" statement and irresponsible to call the vinegar labeled "SB" "blended vinegar".
Nutrition myth 6: The longer the shelf life of food, the more preservatives are added?
Many people think that the food with a long shelf life must be added with more preservatives, which also makes many people pay great attention to its shelf life when buying food. So is the shelf life of food really related to preservatives?
Experts’ doubts: Not all foods with long shelf life are added with preservatives, and many foods on the market can be preserved without preservatives now. For example, some high-salt, high-sugar and high-acid foods, such as liquor and honey, have bacteriostatic effect, and preserves and quick-frozen foods have little water, and can also be preserved for a long time without adding preservatives.
Ma Zhiying, director and senior engineer of the Food Safety Professional Committee of Shanghai Food Society, pointed out that foods that need to be added with preservatives are generally foods that are stored at room temperature, have relatively simple packaging, have certain water content and have shelf life requirements, such as bean products, cakes, soy sauce, carbonated drinks, fruit juice, jam, western-style cooked meat, Chinese ham sausage, packaged pickles, and various dried meats. Among them, soy sauce and jam will not be eaten quickly after opening the package, so preservatives need to be added to prevent spoilage and prolong the storage time.
In addition to adding preservatives, there are many ways to extend the shelf life of food, such as coating, pickling, high temperature and high pressure sterilization, freezing and irradiation, etc., which can be preserved for a long time without adding preservatives.
In addition, we can’t generally say that food with preservatives is unsafe, and food without preservatives is safe. Experts believe that neither preservatives nor food additives can be separated from "quantity". At the same consumption, the toxicity of calcium propionate, a common preservative, is equivalent to that of salt, while the toxicity of potassium sorbate, which is widely used now, is only 1/2 of that of salt. For example, the maximum allowable amount of potassium sorbate per kilogram of packaged pickles is 500 mg. According to an adult’s 50 kg weight, it is allowed to consume 1250 mg of potassium sorbate every day, that is, it takes 2.5 kg of packaged pickles every day to reach this amount. Therefore, there is no need to worry about excessive intake of preservatives in a normal diet.
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