Metabolic water

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.[6] Birds, however, excrete uric acid and can have a net gain of water from the metabolism of protein.

References
  1. Mellanby, Kenneth (July 1942). "Metabolic Water and Desiccation". Nature. 150 (3792): 21. Bibcode:1942Natur.150...21M. doi:10.1038/150021a0. S2CID 4089414.
  2. Morrison, S. D. (1953-11-28). "A method for the calculation of metabolic water". The Journal of Physiology. 122 (2): 399–402. doi:10.1113/jphysiol.1953.sp005009. ISSN 0022-3751. PMC 1366125. PMID 13118549.
  3. 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 (2005). 4 Water | Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate | The National Academies Press. p. 85. doi:10.17226/10925. ISBN 978-0-309-09169-5.
  4. "Racing the wind. Water economy and energy expenditure in avian endurance flight". Archived from the original on 2008-06-29. Retrieved 2008-08-01.
  5. Klaassen M (1996). "Metabolic constraints on long-distance migration in birds". J Exp Biol. 199 (Pt 1): 57–64. doi:10.1242/jeb.199.1.57. PMID 9317335.
  6. Board on Agriculture and Natural Resources (BANR), Nutrient Requirements of Nonhuman Primates: Second Revised Edition (2003), p. 144.
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