On average, 60% of an adult human body consists of water (between 50%-70%). Most of the body water is inside our cells.
The total body water is kept in three major locations: intracellular fluid (two thirds of water), extracellular water fluid, and in our blood (one third of water). For example, a 70-kilo man consists of approximately 42 liters of water:
28 liters of intracellular water,
14 liters of extracellular water,
3 liters of which are blood plasma,
1 liter of which is transcellular fluid (cerebrospinal fluid, ocular, pleural, peritoneal and synovial fluids),
10 liters of which are interstitial fluid (including lymph), an aqueous medium that surrounds the cells.
In fact, the amount of body water varies depending on certain factors: the body of a newborn baby (75%) consists of more water than the body of an elderly person (50%).
In addition, all our vital organs contain a different amount of water: while the brain, lung, heart, liver and kidneys – contain between 65% and 85% of water depending on the organ – the bones contain less water (but still this rate is still 31% ).
How do we measure the body water?
Except for those with obesity, water is the largest component of the body, making up 50-70% of the total mass. The water contents of various tissues differ, but 70-80% of lean tissue usually consists of water, while the fatty tissue contains about 20% water, but there is no clear rate agreed on by academics. For example, according to the Institute of Medicine, this rate is at the level of 10%.
However, the total amount of the body water is an important data in estimating the body composition. the Fat Mass and the Fat Free Mass (FFM) can be estimated based on the assumption that Fat Free Mass contains 72% – 73% water.
However, estimation or determination of the total amount of body water is not so easy as it is a dynamic situation. Approximately 2-3 liters (L/day) of water change place daily in our body. However, in case of heavy diarrhea or physical activities performed in extremely hot environments, this rate can reach 2 liters within 1 hour. Therefore, even if there are many body water measurement methods in the literature, it is of great importance for what purpose and under what conditions these methods are used. For example, the methods that estimate the body fat percentage by making use of body water mass will give seriously misleading results. The Bioelectrical Impedance Analysis (BIA) method is one of the most recognized of them. For a 70-kg individual with 14 kg of fat (20%), a 10% body water loss increases the fat percentage to 21.5%.
Body water measurement methods and devices in the literature;
Deuterium Dilution Method
In dilution methods, by giving a substance to the compartment to be measured, the concentration of said substance in the samples taken is measured. It is the deuterium dilution method that is well-known and most accepted by Schoeller et al. The patient is given an oral dose, blood and saliva samples are taken at 2-4 hour intervals and analyzed using the infrared spectroscopy. This provides 1-2% accuracy. However, body water assessment with this method is not practically usable as it requires specialization in measurement and expensive laboratory equipment. It is used in advanced medical examinations and research.
Significant medical data about body water mass and condition can be obtained from blood values such as hemoglobin-concentration, hematocrit, plasma osmolarity and sodium concentration, plasma testosterone, adrenaline, noradrenaline, cortisol, and atrial-thiethetics.
Data such as volume, color, protein content, specific gravity, and osmolarity also provide significant medical data about body water mass and condition.
Impedance Analysis (BIA and BIS)
First of all, Impedance Analysis is not a device name, but the name of a basic method. Although there are dozens of device types using this method, these devices, which have a serious market today, are manipulated by both manufacturers and users due to commercial concerns.
First of all, impedance analysis is based on the total volume of a conductor, its length (L) and resistance (R), which can be calculated based on an electrical current with single frequency (L2/R).
This principle has been applied to the body composition assessment. The basic assumptions are that the conductor is cylindrical and the current is evenly distributed throughout the conductor. In this rather weak but innovative approach, the total water volume is calculated by making use of the conductivity structure of the cell wall and the conductivity of the body water. As mentioned above, the body fat percentage is given with a number of formulation and verification coefficient based on the assumption that the Fat Free Mass (FFM) contains 72% – 73% water.
However, 3 different methods are used in impedance analysis.
Multi-Frequency BIA (bio impedance analysis): In BIA, it is assumed that the low frequency cannot pass through the cell wall, so that the amount of extracellular fluid with low frequency value is estimated. Total body fluid is estimated assuming that the high frequency can pass both intracellular and extracellular environment. The difference between these two values gives the intracellular fluid value. It estimates body composition values by making use of these data. However, the point to be considered is that BIA devices give instant results, and it is assumed that the total amount of fluid it measures is your ideal body water mass. To ensure this, it prohibits fluid and food intake 4 hours before the measurement, also, it prohibits making exercise or even having bath before the measurement. The main goal is to bring you to your ideal fluid balance and calculate your fat percentage using the total water it measures. All BIA devices agree that the presence of edema at the time of measurement will affect the results. For this purpose, it prohibits taking measurements during menstruation. such BIA devices can be found today in all dietician clinics.
Single-Frequency BIA: It focuses on the total water volume, giving only high frequency. This method is usually used in body weight scales for domestic use.
BIS (Bio Impedance Spectroscopy): This method focuses on the amount of intracellular and extracellular fluid, with more complex formulas and a much wider range of frequencies. It is suitable for medical use because the analysis is taken continuously over a period of time, rather than momentarily. BIA spectroscopy method is widely used in the management of fluid balance to prevent excessive fluid load and dehydration of various patient groups, including hemodialysis and other kidney disease patients. You can see an example of the Bio Impedance Spectroscopy device used for medical purposes in the figure below.
Disinformation and manipulation start right here. Multi-frequency BIA and BIS methods are both multi-frequency methods. However, although their goals and methods differ from each other, BIA manufacturers and suppliers do not mind adding the features of the BIS method to BIA devices. As a result, they claim that they can detect edema with BIA devices, and they can follow the body water during exercise and diet processes. Thus, the users who consider the specifications provided by the manufacturer sufficient for themselves do not hesitate to make this comment to their patients and clients. However, the total body water (TBW) is a pivot value for multi-frequency BIA devices, in other words, a touchstone. This data is considered to be ideal, that is, there is body water balance at that moment, accordingly, the body fat percentage and muscle percentage are formalized and calculated. If you have edema or a little excess water (bladder, stomach, etc.) in your body, your water percentage will be high and your fat percentage will be low, which is a momentary data. It will not be a value that reflects your real body water balance. Therefore, the analysis reports of the Multi-Frequency BIA devices make no comments can be made about your body water percentage and their follow-up cannot be evaluated. If your health counselor or dietician comments as if you have lost such an amount of edema by using the Multi-Frequency BIA device report, you can be sure that she/she manipulates the data to make you happy. If you have edema or your body water is not at balance at that moment, the measurement of the Multi-Frequency BIA device will be incorrect.
In the figure below, you can see the results of regular measurements by a Multi-Frequency BIA device of a known brand. If you examine carefully, you can see that 73% of “Fat-Free Mass (kg)” gives the “fluid mass (kg)”, even though the body mass changes on each date. Likewise, when you subtract -2.2 kg from the value of “Fat-Free Mass (kg)” , you can find the “Muscle Mass (kg)”. In this calculation, 2.2 is the bone mass determined based on the age, height. When you examine a little more, you will see that your fat percentage is calculated by subtracting fat-free mass from your weight and then proportioning it to your weight. In a nutshell, all the BIA devices do is to calculate body composition value using standard and unchanging formulas by estimating the total body water assuming that it is at balance. In this case, instead of following up such a complicated table, it will be sufficient to follow up “Fat Percentage”, “Fat-Free Mass (kg)”, and visceral fat percentage, if provided; since they are more significant figures considering your weight change.
Therefore, if your values are measured using Multi-Frequency BIA devices, which are widely used, please keep in mind the following issues;
Strictly follow the instructions of the device manufacturer, consultant or dietician.
Apart from the instructions given to you, avoid all kinds of things that can disrupt your body water balance. (Such as sweating, lying down for a long time, taking a bath, etc.). The stability of your body water balance is required to get the correct measurement.
If you think you have edema, you should postpone the measurement.
Have your measurements taken as long as possible while you are at the same physical pace and on the same diet program. Have your first measurement taken 1 week after starting a new diet or workout program.
Keep in mind that the value of the body water given is your ideal balance value if all these conditions are met; also, your values of fat percentage and muscle percentage are calculated based on this value considering your total body weight.
If you feel healthy and do not have an ailment, your body will maintain your water balance through the collaboration of various systems in your body. Never make any modification in your diet to maintain your water balance according to your results. Generally, edema complaints are eliminated with regular workout program and healthy nutrition. However, if you have long-term and recurring edema complaints, you should consult a physician.
In this article, we tried to give information about total body water mass measurement methods and devices used in the literature. In our second article on this subject, we will give information about more practical methods.