Determining the amount of fat in the human body can be done by measuring total body water (TBW) with isotopes. The human body can be thought of as being composed of two categories: fat mass, and fat-free mass. There is no water in fat mass, whereas 73–80% of fat free mass consists of water. The fat-free mass of a newborn baby contains 80% water, and this gradually decreases to 73% in adults. This means fat-free mass can be determined by measuring TBW and then using an appropriate hydration factor. Hydration factor was developed to be the most effective way to ensure the water you drink provides your body with overall hydration. There are many methods for determining hydration status, including monitoring body mass changes, measuring various blood markers, and analysis of urine. That urine analysis has been shown to be most valid and reliable method for determining moderate changes in fluid balance.
The deuterium dilution technique involves measuring a person’s saliva and/ or urine just before they consume a dose of deuterium labeled water and repeating the process 3 to 5 hours later. The increased level of deuterium shows in the person’s saliva and urine samples. The deuterium is evenly distributed throughout the body after 3 to 5 hours. The person’s pre-dose samples of urine or saliva are compared with the post-dose samples to calculate TBW, fat-free mass and ultimately the amount of fat in the body. Body composition is a good indication of health. Too much fat or too little fat-free mass raises the risk of serious health conditions.
References:
1. How isotope techniqes help nutrition, IAEA Bulletin 55-1-March 2014.
2. Body composition by hydrometry, ME Valencia1, H Alema´n-Mateo1, International Journal of Obesity 2003.
