Body Water

Body Water

In a survival scenario, the “rule of three” refers to the priorities that the human body needs to survive. In a hostile environment, you can survive without food for 3 weeks, without water for 3 days, without shelter for 3 hours, and without air for 3 minutes. It goes without saying that water in the body is an important aspect of bodily function, and that proper hydration is necessary for ideal organ function, thermoregulation, blood flow, and overall health.

Normal Range The normal range of body water varies with age and gender. Infants tend to have higher body water (about 75%), which decreases with age and remains relatively stable throughout adulthood. In general, men (50-65%) tend to have more body water than women (45-60%).

(PS： body water can change significantly during pregnancy)

Particularly interesting is the fact that body water is strongly correlated with muscle mass.A 2019 study published in the Journal of Nutrition, Health and Aging confirms that researchers found a correlation coefficient of 0.89 between body water and muscle mass, and that body water is also positively correlated with Barthel Index scores (functional performance) and stride speed in both men and women.

This is due to the high water content of muscle and the relatively low water content of fat. (Note that this is a key principle utilized by the bioelectrical impedance analysis technique!) . As a result, people with more body fat tend to have a lower percentage of water in their bodies compared to people with less body fat. For example, a person with 20% body fat will have a higher percentage of water in their body compared to a person with 40% body fat.

There are a variety of recommendations about how much water a person should drink each day. The traditional “X glasses of water a day” guideline is sometimes challenged by the seemingly intuitive advice to “drink water when you feel thirsty.” Other common advice includes “Your urine should be clear, not yellow. Yellow color is a sign of dehydration.”

What does it mean to be dehydrated?

Generally, dehydration - i.e. not enough water in the body - is caused by not drinking enough fluids, or losing more fluids than you take in. Physical activity (especially in hot weather), diet, or illness (such as fever, persistent vomiting, or diarrhoea) can lead to dehydration if there is insufficient fluid replacement. Dehydration of the body results in a variety of physical symptoms such as dark yellow urine, thirst, headache, fatigue, muscle cramps, and an inability to function normally.

In most cases, the easiest way to treat dehydration is to rehydrate by drinking plenty of water. In severe cases, an intravenous drip may be necessary to replenish essential nutrients at a faster rate than drinking water.

Is it possible to be "overhydrated"?

Generally speaking, the body automatically and efficiently self-regulates water in the body, and it's hard to get “overly dehydrated” by drinking too much water because you'll naturally develop the urge to excrete water and maintain a normal balance.

However, it is also possible for the body to accumulate too much water or to fail to expel it properly! This excess water is known as “water weight.” Various diseases caused by kidney or heart problems, etc., have been linked to excess weight because the body has difficulty maintaining proper balance.

For healthy people, temporary water retention in the body is not necessarily a health problem. For example, increased salt intake can lead to water retention.

Why is it important to estimate your body water?

For example, when people go on a “diet” (usually referred to as a diet that restricts calorie intake), water weight is usually the first thing to go down before body fat begins to decrease significantly. Therefore, if you notice that you are losing weight on the scale, the first thing you need to do is to make sure that this is actually a loss of body fat, or just a loss of water.