What is Doubly labeled water?
In fact, oxygen-18 is present in nature, and to produce it, it is sufficient to isolate it from other stable isotopes of oxygen. In the process of producing oxygen-18, first, its intermediate product is enriched in the form of a D218O molecule. This product is used as doubly labeled water by deuterium and oxygen-18 isotopes to study the metabolic rate of living organisms. In this method, animals are fed with D2 18O for a few days with a special isotopic richness. Deuterium is excreted from the body by water, urea, and oxygen-18 by water and CO2. By determining the isotopic ratio of these compounds, the body can be metabolically studied and the amount of CO2 produced can be measured. This method was first described by Lifson et al. To study energy metabolism in small animals and was later extensively evaluated in adults and infants by Schoeller and other researchers.
Use the doubly labeled water technique to measure energy consumption
Measuring energy consumption with doubly labeled water is an indirect calorimeter (calorimeter), in which the energy consumption of living organisms is obtained by measuring the production of carbon dioxide. It was first discovered in 1949 that oxygen in respiratory carbon dioxide is in isotopic equilibrium with oxygen in the body's water.
The use of doubly labeled water to measure the energy consumption of living organisms was first used in humans in 1982. In the labeled water method, by tracing the stable isotopes deuterium and oxygen-18 to measure total energy consumption to determine The need for energy and energy balance is used in humans. Basis In this method, the carbon dioxide produced can be measured by the difference between the amount of hydrogen and oxygen excreted in the body. Thus, after oral administration, some water is labeled twice with the isotope deuterium and oxygen-18, deuterium in the form of water, and oxygen-18 in the form of water and carbon dioxide are excreted from the body. Within two weeks, the excretion of deuterium and oxygen-18 isotopes is measured by periodic sampling of body water, which is sampled from human urine, saliva, and plasma. The difference between the excretion is the amount of carbon dioxide production Measured and then using the indirect calorimetric method, carbon dioxide produced is used to calculate the total energy consumption. It should be noted that the direct calorimetric method provides a measurement of energy consumed as heat, but the calorimetric technique Direct has many disadvantages.
The advantages of the doubly labeled water method
The doubly labeled water method to measure energy consumption based on estimates of CO2 excretion from the body. This method has become a popular method due to several obvious advantages:
1- This method determines the amount of energy consumption, which includes the total energy consumption, rest energy consumption, food heat effect, and activity heat.
2- This method is simple to use and the person can perform their normal daily activities during the measurement and there is no limit in the person's life.
3- This method shows the total amount of energy consumed daily and is suitable for infants, young children, the elderly, and disabled people who can not easily withstand the harsh conditions of measuring oxygen consumption.
4- With the double watermark method, the estimated energy intake of energy consumed in the list of physical activities can be validated
5- The most important advantage of this method is the high accuracy of about 2 to 8%.
6. CO2 emissions over a long period are measured in hours to days and therefore include a combined measure of energy consumption over the entire period.
Limitations and disadvantages of using doubly labeled water
The relatively high cost of equipment required for the analysis of stable isotopes, as well as the need for specialists to work with them, has made the use of double-labeled water more commonly used for research and not for everyday use by physicians. Provides physicians with energy to estimate total needs. These equations are used only as a guide or starting point, after which the person is fully monitored and the necessary interventions are made to improve the proper nutritional status for him. Like many equations, these equations apply to healthy people and do not apply to sick people or those who need special nutritional support.
You can also find other articles about the above keywords in other languages with the use of these words.
doubly labeled water: in Chinese: 双标签水 \ in Germany: doppelt gekennzeichnetes Wasser
in Russia: дважды маркированная вода \ in Italy: acqua doppiamente etichettata