metabolic water
{{Short description|Water created by metabolism in living creatures}}
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,{{cite journal |last1=Mellanby |first1=Kenneth |title=Metabolic Water and Desiccation |journal=Nature |date=July 1942 |volume=150 |issue=3792 |pages=21 |doi=10.1038/150021a0 |bibcode=1942Natur.150...21M |s2cid=4089414 |doi-access=free }} 41–42 grams of water per 100 g of protein, and 60 grams of water per 100 g of carbohydrate.{{Cite journal|last=Morrison|first=S. D.|date=1953-11-28|title=A method for the calculation of metabolic water|journal=The Journal of Physiology|volume=122|issue=2|pages=399–402|doi=10.1113/jphysiol.1953.sp005009|issn=0022-3751|pmc=1366125|pmid=13118549}}{{Cite book|url=https://www.nap.edu/read/10925/chapter/6#85|title=4 Water {{!}} Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate {{!}} The National Academies Press|year=2005|isbn=978-0-309-09169-5|pages=85|doi=10.17226/10925|last1=Medicine|first1=Institute of|last2=Board|first2=Food Nutrition|last3=Intakes|first3=Standing Committee on the Scientific Evaluation of Dietary Reference|last4=Water|first4=Panel on Dietary Reference Intakes for Electrolytes and}}
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.{{cite web |url=http://dissertations.ub.rug.nl/faculties/science/2005/s.b.engel/ |title=Racing the wind. Water economy and energy expenditure in avian endurance flight |access-date=2008-08-01 |url-status=dead |archive-url=https://web.archive.org/web/20080629062143/http://dissertations.ub.rug.nl/faculties/science/2005/s.b.engel/ |archive-date=2008-06-29 }}{{cite journal |author=Klaassen M |title=Metabolic constraints on long-distance migration in birds |journal=J Exp Biol |volume=199 |issue=Pt 1 |pages=57–64 |year=1996 |doi=10.1242/jeb.199.1.57 |pmid=9317335 |bibcode=1996JExpB.199...57K |url=http://jeb.biologists.org/cgi/pmidlookup?view=long&pmid=9317335}} Humans, by contrast, obtain only about 8–10% of their water needs through metabolic water production.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]
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.