Myths that should be forgotten forever

Is 2 liters of water a day really the standard? New scientific research questions the common advice. It turns out that what we have heard and believed is not entirely true. Let's figure out what affects the need for water, and why 2 liters is not the standard, it is not one and for everyone.

Hydration: What's happening inside the body

A person can survive 3 minutes without oxygen, 30 days without food, and 3 days without fluids—that's how hydration works. Without water, nothing in our bodies works at all. 

The body of a newborn is 80% water. As we get older, the proportion of water decreases and reaches about 60%. The vitreous body of the eye is 99% water. The fluid content of the muscles is about 80%. 

Every day, our body loses about 2 liters of water: partly through the skin, which regulates body temperature. The kidneys, which rid our body of toxins, excrete fluid in the form of urine. The fluid is excreted with feces through the intestines. We also lose water in tiny droplets when we breathe.

Therefore, the body needs a constant supply of fluid. It is necessary to transport nutrients, remove waste, carry out chemical reactions, lubricate and cushion joints. But the statement that an adult must drink at least 2 liters of water per day is the result of a misinterpretation of expert recommendations.

The myth about 2 liters: where did this number come from?

In a 1945 document, the Food and Nutrition Commission of the National Research Council (NRC) recommended drinking 1 ml of water for every calorie consumed. By this logic, a person consuming 2,000 calories per day would need to drink the same 2 liters, or 8 glasses, of water. 

But there is a fundamentally important nuance: the NRC recommendations were not just about water, but about any drinks and products that contain liquid. 

Updated recommendations

In 2022, scientists from the University of Aberdeen in Scotland officially updated the current widespread recommendations. Before that, they conducted a large-scale study involving 5,604 people from 23 countries, aged from 8 days to 96 years. According to the results, about half of the daily norm — about 1 liter of fluid — a person receives with food.

Professor John Speakman, one of the authors of the study, concludes that the original measurement of the daily requirement of 2 liters is the result of an error. The water we should drink is the difference between our total daily requirement and what we get from food.

The fluid ingested with food was measured with the utmost precision using stable isotope technology. The experiment also measured the rate at which fluid was excreted from the body. The most important factor determining this was the amount of energy expended. 

Several factors affect the rate of water removal and energy consumption:

• air temperature; 
• activity during the day;
• health status;
• nutritional features.

In practical dietetics and nutrition, the average fluid requirement of an average European is calculated as 30-40 ml per 1 kg of weight. In this case, in the cold, with low activity, normal body temperature, etc., a coefficient of 30 is taken, and in the heat, with high activity and high body temperature, a coefficient of 40 is taken.

What to pay attention to

When the body does not have enough water, the blood volume decreases, but the amount of salt and other minerals remains unchanged, that is, their concentration in the plasma increases. An increase in the concentration of soluble substances by 2-3% causes a reaction of neurons in the "thirst area" of the brain. This is how a person feels the desire to drink. 

And it is your own desire to drink that you should pay the most attention to.

At the same time, if you don't get enough fluids from drinks and food, your urine will turn a deep yellow color, which is the second indicator. You can also monitor your fluid intake using gadgets.

The main thing that the updated study shows is that the popular idea of 8 glasses of water per day for most people is overestimated in most situations. And scientific data does not support the existence of a single standard for all people.