Metabolic water explained

Metabolic water refers to water created inside a living organism through metabolism, by oxidizing energy-containing substances in food and adipose tissue. Animal metabolism produces about 107–110 grams of water per 100 grams of fat,^[1] 41–42 grams of water per 100 g of protein, and 60 grams of water per 100 g of carbohydrate.^{[2] [1] [3]}

Some organisms, especially xerocoles — animals living in the desert — rely exclusively on metabolic water. Migratory birds must rely exclusively on metabolic water production while making non-stop flights, facilitated by the high metabolic rate during such flights.^{[4] [5]} Humans, by contrast, obtain only about 8–10% of their water needs through metabolic water production.^[6]

In mammals, the water produced from metabolism of protein roughly equals the amount needed to excrete the urea which is a byproduct of the metabolism of protein. Birds, however, excrete uric acid and can have a net gain of water from the metabolism of protein.

Notes and References

1. Mellanby . Kenneth . Metabolic Water and Desiccation . Nature . July 1942 . 150 . 3792 . 21 . 10.1038/150021a0 . 1942Natur.150...21M . 4089414 . free .
2. Morrison. S. D.. 1953-11-28. A method for the calculation of metabolic water. The Journal of Physiology. 122. 2. 399–402. 10.1113/jphysiol.1953.sp005009. 0022-3751. 1366125. 13118549.
3. Book: 4 Water Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate The National Academies Press. 2005. 978-0-309-09169-5. 85. 10.17226/10925. Medicine. Institute of. Board. Food Nutrition. Intakes. Standing Committee on the Scientific Evaluation of Dietary Reference. Water. Panel on Dietary Reference Intakes for Electrolytes and.
4. Web site: Racing the wind. Water economy and energy expenditure in avian endurance flight . 2008-08-01 . dead . https://web.archive.org/web/20080629062143/http://dissertations.ub.rug.nl/faculties/science/2005/s.b.engel/ . 2008-06-29 .
5. Klaassen M . Metabolic constraints on long-distance migration in birds . J Exp Biol . 199 . Pt 1 . 57–64 . 1996 . 10.1242/jeb.199.1.57 . 9317335 .
6. Board on Agriculture and Natural Resources (BANR), Nutrient Requirements of Nonhuman Primates: Second Revised Edition (2003), p. 144. http://books.nap.edu/openbook.php?record_id=9826&page=154