#42: What Is ‘Total Body Water’?
For the most part, the human body is comprised of water. And considering the physiological importance of water, it goes without saying that this storage is absolutely necessary for human survival.
Age (the older the animal, the higher its relative bone mass and the lower its body water content), sex and hydration levels are key determinants of our TBW. But one major factor that is often ignored is that of lean body mass. More water is stored in muscle than in fat tissue.
Lean body mass is the difference between total body weight and body fat weight. This means that it counts the mass of all organs except body fat, including bones, muscles, blood, skin, and everything else.
What Should Our Baseline TBW Be?
A conventional reference range for an adult’s body water percentage is shown in the image below but the TBW percentage can range from anywhere to 45% to 75%.
In one, massive study done on adults of all ages and both sexes, the adult human body averaged around 65% water. However, this varied substantially by age, sex, and the amount of body fat they had. Some obese folks accrued as little as 45% water.
Water Is Needed For Almost Every Bodily Function
Most of the body’s systems require water in order to function properly. It is the only essential fluid in existence, playing a key role in temperature regulation, cellular function and waste removal. It also helps to keep our joints lubricated while aiding in the protection organs and tissues.
Water makes up 79% of your muscles, 73% of your brain and even 31% of your bones, and makes up most the following fluids:
intracellular fluid
extracellular fluid
plasma
interstitial fluid
transcellular fluid
Organs aside, water is also found in gastrointestinal, cerebrospinal, peritoneal and ocular fluids.
Muscular Folks Will Store More Water
Fatty tissue contains less water than muscle. So basically, the more muscle you have, the more water your body will have. This is why females typically have lower levels of TBW: simply because they have higher levels of body fat when compared to their male counterparts.
Fat tissue is about 10% of water, while muscle tissue contains about 75%.
Although men typically have more TBW than females, babies take the cake as far as the highest TBW goes. In fact, the average child is approximately 70% water.
Water Intake: How Much Of It Is ‘Normal’?
There is no hard-and-fast rule. But directing your intake based on the colour of your urine is a useful and easy measure of your hydration level.
At most times, the colour of your urine should be straw coloured. If the fluid is a concentrated yellow, then perhaps you should have a glass of water, STAT.
Water can also enter the body through food, especially those rich in water (plants, raw meat and fish are typical examples).
Not drinking enough water can lead to dehydration, and that brings with it a host o problems that don’t stop at a decline in athletic performance.
Dehydration is a loss of water in the body. This does not only depend on the amount of water consumed, but on certain electrolytes too.
Sodium loss correlates with fluid loss from extracellular fluid. This happens because the extracellular fluid has a much higher concentration than the intracellular fluid).
Potassium, in turn, has a much higher concentration in the intracellular fluid, than in the extracellular fluid. Therefore, loss of potassium is associated with fluid loss from the intracellular fluid since potassium loss from extracellular fluid causes the potassium in the intracellular fluid to diffuse out of the cells, dragging water with it by a process known as osmosis.
Water Retention Can Provide Clues That Point Towards Disease States
TBW is regulated by hormones (anti-diuretic hormone, aldosterone and atrial natriuretic peptide).
Doctors, thus, can be given an indication of a present disease state based on which fluid compartment of the body is affected. This is why it could provide an important snapshot at the state of human health, at least in some cases.
