Can milk be drunk as water? Yes, and no.
Saying milk can be drunk as water is because nearly 90% of its composition is water. Water is one of the most essential nutrients for maintaining human life. When the body loses more than 2% of its water, its functional operation is affected. Without water replenishment, human life can be in danger within a few days. Therefore, when the water supply is insufficient, milk can naturally serve as a source of water to replenish the body's precious water.
However, milk cannot be drunk as water. This is because we can drink as much water as we need, but not so with milk. The reason is that milk also contains many other components such as fat, protein, sugar, calcium, and phosphorus, and the intake of all these has limits. If our daily water needs are all met by milk, the intake of nutrients like fat may become excessive. Therefore, milk cannot be drunk in unlimited quantities as a substitute for water.
"High-nutrition" foods are not always "the more, the better."
People who think milk can be drunk as water are operating under the assumption that milk is a high-nutrient beverage and that "high-nutrition" therefore means it should be consumed in large quantities. Some people have a misunderstanding of "nutrition." They interpret it as the quantity and quality of various nutrients. Milk is rich in calcium, has high-quality protein, and contains relatively high amounts of Vitamin B2 and Vitamin A, which are often insufficient in the Chinese diet, hence it is considered "nutritious." But why is this a misunderstanding?
Firstly, so-called nutrition refers to a reasonable combination of various foods in terms of quantity and variety to meet the body's needs. Due to current limitations in nutritional science, this rationality is often expressed as the quantity and proportion of various nutrients. However, this does not mean that simply putting proteins, vitamins, calcium, iron, zinc, and other nutrients together becomes "high-nutrition." A reasonable nutritional food combination should include a certain proportion of grains, legumes, vegetables, fruits, meat, eggs, milk, and other foods, plus water, to form our daily meals. Using large amounts of milk instead of water actually disrupts this balance of food combination.
Secondly, analyzing the nutrients it contains, milk's protein and fat content are both around 3%, sugar content is about 5%, and calcium is about one-thousandth. According to the Chinese Dietary Guidelines' recommendation of 1.2 liters of daily water intake, if milk is drunk as water, calcium would be supplied in excess, and fat and energy would also be a bit too much. The saturated fatty acids in milk are not good for cardiovascular health, and too much energy can easily lead to obesity. Even if milk replaces half of the daily water intake—600 milliliters—the intake of fat and energy is still considered excessive. This is why Westerners choose skim milk for health reasons. As for the protein in milk, we don't really need to overemphasize it. Due to the current abundance and variety of food supplies and the relatively high proportion of animal-based foods, protein intake for the urban population in China is no longer their main nutritional concern. For rural residents, especially those in less developed rural areas, milk plays a more significant role in improving protein nutrition.
Finally, it should be noted that high-protein, high-fat, and high-energy diets have become one of the main culprits of modern "civilization diseases" such as diabetes, cardiovascular diseases, and tumors. Therefore, regarding the Western habit of drinking large amounts of milk and using it as a substitute for water, some scholars hold a very negative view. Based on some reports linking milk to ovarian and prostate cancer, some scholars even advocate not drinking milk at all. This is somewhat extreme. The occurrence of cancer is related to many of the foods we eat daily and our eating habits, such as consuming large amounts of animal-based foods, fried and grilled foods, and smoked and pickled foods, excessive energy intake, and insufficient consumption of vegetables and fruits. The relationship between these issues and cancer is greater than that with milk. Therefore, we cannot "stop eating for fear of choking," nor can we simply interpret these studies as a direct causal relationship between a certain food and tumors. We should recognize that any food has both beneficial and harmful aspects;适量 is beneficial, while excessive is harmful, and the key is a balanced combination of various foods.
So, if we can drink some milk every day, it can improve our calcium supply, and it is also acceptable as a temporary water source when drinking water is inconvenient. However, using large amounts of milk as a long-term substitute for drinking water by no means constitutes reasonable nutrition, let alone high nutrition; it may even bring health hazards.