"In our daily lives, water is just too ordinary and common. But precisely because of this, most people don't understand how much water they should drink, what kind of water to drink, or when to drink it... and this directly affects our health," said Professor Cheng Yiyong, Vice Chairman of the Chinese Nutrition Society, to a reporter from *Life Times*. For this issue, we have invited Professor Li Lite, Vice Chairman of the National Food and Nutrition Advisory Committee and Professor at the College of Food Science and Nutritional Engineering at China Agricultural University; Wang Yi, Director of the Dietetic Nutrition Department at Guang'anmen Hospital, China Academy of Chinese Medical Sciences; and Professor Cheng Yiyong to answer 10 "water-related questions" that are closely linked to our health and are of most concern to the public.
Q1: What exactly is in water nutritionally?
Li Lite: Indeed, many people are concerned about whether water contains various nutrients, but they overlook a most fundamental fact—water itself is a nutrient. When we talk about the six major nutrients the human body needs, we are actually referring to carbohydrates, fats, proteins, vitamins, minerals, and water. Water is essential for life, an indispensable nutrient for the survival of animals and plants. At the same time, water is also the most abundant component in the human body. With sufficient water intake, a person can survive for several weeks without food; but without water, a person will die in a few days. Therefore, whether you love drinking plain boiled water, tea, or soup, you must consume enough "water nutrition" daily to keep this complex machine of the human body running normally.
Q2: Is plain boiled water the most effective for rehydration?
Cheng Yiyong: This statement is somewhat one-sided. Plain boiled water is indeed effective for rehydration, but because of its single taste, it might make people feel "unpleasant to drink." Research indicates that people tend to consume more water when drinking their favorite beverages.
The latest edition of the *Dietary Guidelines for Chinese Residents* by the Chinese Nutrition Society also points out that the vast majority of beverages on the market contain over 80% water. The main function of beverages is to replenish the water needed by the body, while also providing consumers with a pleasant taste experience. However, many beverages contain a certain amount of calories, which will increase calorie intake while rehydrating. Therefore, when drinking beverages like cola, it is important to control the amount. Besides plain boiled water, drinking a glass of milk in the morning or a glass of juice between meals are also good choices.
Q3: What are the nutritional differences between plain boiled water, purified water, and mineral water?
Li Lite: In terms of composition, both plain boiled water and mineral water contain minerals, while purified water is simply water. In northern China, for example in Beijing, a thick layer of scale forms on the inside of a kettle used to boil water, which is a manifestation of the presence of minerals. In this sense, plain boiled water is also a type of mineral water. But does water containing minerals have to be better than water without it? Not necessarily. After all, the mineral content in water is very low and will not have a significant impact on supplementing the minerals needed by the human body. Therefore, it is wrong to say that long-term consumption of mineral water will lead to excessive mineral intake or even poisoning, and it is also wrong to say that long-term consumption of purified water will lead to malnutrition.
Q4: Can drinking soup rehydrate you?
Cheng Yiyong: Of course it can, because more than 90% of soup is water, making it a good way to rehydrate. However, the soup should not be too salty, otherwise, excessive intake of sodium ions will change the osmotic pressure in the body, forcing you to drink more water to neutralize it—that's why we sometimes feel thirstier the more soup we drink. Therefore, it is crucial to control the amount of salt when making soup. Chicken and mushroom soup are already very savory and can be made without salt.
Q5: Is overnight water really drinkable?
Li Lite: Some microorganisms might multiply in overnight water, but it's not as severe as to say it is very harmful to the human body. As long as it is not contaminated, the properties of the water will not change, so drinking overnight water is not a problem. The spring water we drink could be from hundreds of thousands of years ago.
Q6: Can you drink water that has been boiled repeatedly?
Wang Yi: Some people also call this kind of water "re-boiled water," referring to water that is repeatedly heated in a water dispenser or kettle. Generally, this water will have a higher nitrite content. A large amount of nitrite can cause direct poisoning, as it reacts with human blood to form methemoglobin, causing the blood to lose its oxygen-carrying function and leading to hypoxic poisoning. Although the nitrite content in re-boiled water is not that high, when it reaches a certain dose in the human body, it can be a carcinogenic, teratogenic, and mutagenic substance, seriously harming human health. Therefore, try not to boil water repeatedly. The hot water from a water dispenser should also be "heated as you drink," and it should not be kept in a constant "heating-insulating" state.
Q7: Is the pH value of water really important?
Li Lite: In the 1990s, Japan developed electrolyzed water, which uses electrodes to treat water into acidic water for sterilization and alkaline water for health. The effects of these two types of water were recognized by the Japanese Ministry of Health and Welfare. However, this alkaline water requires a pH value of 8.5 or higher to have functions such as reducing stomach acid and regulating intestinal flora. Currently, some "weakly alkaline" waters on the market claim that drinking them can change the body's acid-base state, which is impossible and is basically just a marketing gimmick.
Q8: Can drinking water detoxify the body?
Li Lite: First of all, what is "detoxification"? No one has been able to clearly define this concept yet. However, human metabolism requires water, and drinking more water can promote gastrointestinal motility and relieve bowel movements. From this perspective, saying that drinking more water can detoxify the body is not wrong.
Q9: How much is the "eight glasses of water" a day?
Cheng Yiyong: This question does trouble many people, because the size of the glasses people use for drinking water is different. In our new Dietary Pagoda, we have added a visual representation of water to emphasize the importance of adequate hydration. For adults with light physical activity living in a temperate climate, the minimum daily water intake is 1,200 milliliters, which is equivalent to two bottles of mineral water, making it very concrete. Some people may ask, it has always been said that daily water intake should not be less than 2,000 milliliters, why is it only 1,200 milliliters now? In fact, 2,000 milliliters refers to the total amount of water a person needs in a day. Fruits and vegetables contain a lot of water, and even staple foods and meat contain water. A large part of the water the human body needs comes from food.
Q10: How should you drink water in the morning after waking up and before going to bed at night?
Wang Yi: The first glass of water in the morning is "life-saving water" because after a night of metabolism, all the waste in the body needs to be flushed out. Our cells are like a dry sponge; when water enters, it absorbs it, and then it is excreted out in about 40 minutes. This metabolic process is what we call detoxification. It is best to choose one of the following three types of water for the morning: the first is clear water, such as plain boiled water, purified water, or mineral water, which can reduce the viscosity of human blood; the second is lemon water, as citric acid can increase appetite in the morning, and its small molecules do not affect kidney metabolism and are beneficial for urination; the third is light salt water, which is very good for people with constipation.
As for evening hydration, you can choose honey water, milk, or yogurt, but people who are prone to getting up at night should try not to drink water right before bed. In addition, if you get up at night, you can drink a glass of water. For those who don't get up at night, just drink it in the morning.