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.