Determination of the energy expenditure, sources, and loss of water among young adults

BACKGROUND: Few studies on measuring human energy expenditure with the doubly labeled water method has been conducted in China. The sources and loss of water among human body have never been systematically evaluated. Less data can be available for the development of the recommendation on energy expenditure and water intake. The objective of this study was to determine the energy expenditure, water sources, and loss among young adults. METHODS: In this cross-sectional study, 25 participants were recruited. Double-labeled water was used to determine their energy expenditure. Water loss through skin evaporation and respiration of the lungs and water sources from metabolic water were calculated using corresponding formula, respectively. Water loss through excretion of urine was recorded and evaluated using “3-day, 24-h, real-time urine excretion record” method. All urine samples were collected and weighed in the 3 days. Water loss through excretion of feces was evaluated using “3-day, 24-h, real-time fecal-excretion record” method. All fecal samples were collected and tested by the direct drying method. Water sources from fluid intake were recorded by “7-day, 24-h, real-time fluid intake record” method. Water intake from food was calculated and tested by the weighing method combined with the duplicate portion method and the direct drying method in the 3 days. RESULTS: The energy expenditure of males was 2187 kcal/d, and that of females was 1987 kcal/d. The median fluid intake, water intake from food, and metabolic water were 887, 1173 and 246 mL, respectively, which accounted for 38.8%, 50.3%, and 11.2% of total water sources. There was a gender difference in the percentage of metabolic water (Z = − 2.135, P = 0.033). The water loss through urine excretion, skin evaporation, respiration, and feces excretion was 1295, 172, 149 and 64 mL, respectively, which accounted for 76.5%, 10.3%, 9.5%, and 3.6% of the total water losses. Gender differences in the amount of water loss through respiration and skin evaporation were found (Z = − 4.125, P < 0.001; Z = − 3.723, P < 0.001). CONCLUSIONS: Energy expenditure of male was higher than that of female. The first major water sources was water intake from food in this study, and the first major water loss was urine excretion. Trial registration The study was registered on the website of Chinese clinical trial registry, and the code of identification is ChiCTR1900028746. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12986-022-00668-2.