Metabolic water

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Metabolic water refers to water created inside a living organism through their metabolism, by oxidizing energy-containing substances in their food. Animal metabolism produces about 110 grams of water per 100 grams of fat,[1] 41.3 grams of water per 100g of protein and 55 grams of water per 100g of starch.[1][2]

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.[3][4] Humans, by contrast, obtain only about 8-10% of their water needs through metabolic water production.[5]

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


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  4. ^ Klaassen M (1996). "Metabolic constraints on long-distance migration in birds". J Exp Biol 199 (Pt 1): 57–64. PMID 9317335. 
  5. ^ a b Board on Agriculture and Natural Resources (BANR), Nutrient Requirements of Nonhuman Primates: Second Revised Edition (2003), p. 144. [1]