The necessity of water
Water is the most abundant substance in our bodies and supports all life activities. Water makes up 55-60% of an adult's body. Organs and tissues such as the brain, intestines, kidneys, muscles, and liver have a relatively high water content of around 80%. However, adipose tissue (subcutaneous tissue) has a low water content of approximately 33% due to its high triglyceride content.
Women have a higher body fat percentage than men, resulting in a lower water content of approximately 55%. Obese individuals also have a lower body water content than lean individuals. Furthermore, as the number of solid cells decreases with age, the water content of elderly individuals is lower than that of adults, at approximately 50%.
The function of water
The main functions of water are dissolving substances, transporting substances, and regulating body temperature.
Dissolution of substances
Nutrients in food are broken down into easily absorbable forms and then metabolized. Metabolic reactions take place in a water-soluble state.
Transport of materials
Blood and lymph, which contain water, transport substances within the body to the cells. Waste products that are no longer needed are also excreted through urine.
Body temperature regulation
Water has a high specific heat (the amount of heat required to raise the temperature of a substance by 1 degree Celsius per gram), meaning it heats up slowly and cools down slowly. Because water's temperature doesn't change much, it helps maintain a constant body temperature.
For example, sweating during hot summer days or exercise helps to dissipate body heat and prevent the internal body temperature from rising.
What is the recommended daily intake of water?
While the intake of nutrients is determined by dietary reference intakes, there are no set reference values for water. However, water is essential for the human body.
Water can be categorized into "intake water," which is drinking water and water contained in food, and "metabolic water," which is produced in the body when nutrients are converted into energy. The total amount of intake water and metabolized water per day is approximately 2,500 ml. This is broken down as follows: approximately 1,200 ml from drinking water, approximately 1,000 ml from food, and approximately 300 ml from metabolic water.1 )
In addition, approximately 2,500 ml of ingested water is excreted per day, including urine, feces, and insensible water loss (water that naturally evaporates through the skin and respiration ) . Approximately 1,600 ml is excreted through urine and feces, and approximately 900 ml through respiration and sweat.1 )
The human body maintains a balance between daily fluid intake and output, so urine output is regulated by fluid intake.2 ) When it is hot, like in summer, and you sweat a lot, it is important to replenish fluids. When you feel thirsty, dehydration has already begun.
How much water should I drink each day?
So, how much water should we drink each day?
According to research in Europe and the United States, the recommended daily water intake is estimated to be around 2.3 to 2.5 liters for groups with low levels of physical activity and around 3.3 to 3.5 liters for groups with high levels of physical activity.3 )
Furthermore, since food accounts for approximately 20% to 30% of water intake in Western countries, and beverages make up the remaining 70% to 80%, it is recommended to drink 1.5 liters of water per day for hydration.2 )
However, the proportion of water intake from food is expected to differ from that of Western countries, as Japanese cuisine, with its high water content, is a factor in the water intake of Japanese people.
However, currently, there are very few reliable studies on water intake and sources among Japanese people, and no useful reports to refer to. Furthermore, the scientific basis for calculating water requirements by sex, age, and physical activity level is still insufficient, so further research is expected.
What happens if you don't drink water?
The human body can survive for nearly a month without food, as long as it has water. However, if it cannot drink even a single drop of water, it becomes difficult to sustain life within two to three days.
A 1% loss of body water causes thirst, a 2% loss can lead to dizziness, nausea, and loss of appetite, and a 10-12% loss can cause muscle cramps and fainting, while a 20% loss can be life-threatening and lead to death.
When the body is dehydrated, it can increase the risk of various health problems, including heatstroke, cerebral infarction, and myocardial infarction.1 )
The health benefits of water
Create a lean physique
Drinking room temperature water warms your body from the inside and boosts your metabolism. It also ensures that blood is properly delivered to your muscles, leading to more efficient muscle growth. Increased muscle mass leads to a higher basal metabolic rate, resulting in a leaner physique.
Thins the blood
Thick, viscous blood is a condition where there is a large amount of fat and other substances in the blood, preventing it from flowing smoothly. Since blood carries oxygen, poor blood flow means that cells don't receive enough oxygen, leading to a weakened immune system and impaired brain and organ function. It can also increase the risk of stroke and heart attack. Drinking water increases the frequency of urination, which helps to eliminate waste products and thin the blood.
Don't overeat (be able to control your food intake)
Drinking water while eating slows down your eating pace and helps you feel full, preventing overeating. Eating quickly makes it harder to feel full, leading to overeating.
Keeps skin moisturized
Even if you apply moisture to the surface of your skin, it won't reach the inside. To hydrate your skin from within, you need to drink water. Also, by replenishing water, waste products and toxins are expelled from within the cells, and essential nutrients are supplied to the cells, so old cells are replaced with new ones, improving skin metabolism and reducing blemishes, wrinkles, and dullness.
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