title: Increased fat catabolism sustains water balance during fasting in zebra finches.
abstract: Patterns of physiological flexibility in response to fasting are well established, but much less is known about the contribution of water deprivation to the observed effects. We investigated body composition and energy and water budget in three groups of zebra finches: birds with access to food and water, food-deprived birds having access to drinking water and food-and-water-deprived birds. Animals were not stimulated by elevated energy expenditure and they were in thermoneutral conditions; thus, based on previous studies, water balance of fasting birds was expected to be maintained by increased catabolism of proteins. In contrast to this expectation, we found that access to water did not prevent reduction of proteinaceous tissue, but it saved fat reserves of the fasting birds. Thus, water balance of birds fasting without access to water seemed to be maintained by elevated fat catabolism, which generated 6 times more metabolic water compared with that in birds that had access to water. Therefore, we revise currently established views and propose fat to serve as the primary source for metabolic water production. Previously assumed increased protein breakdown for maintenance of water budget would occur if fat stores were depleted or if fat catabolism reached its upper limits due to high energy demands.
authors: Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, Kraków 30-387, Poland joanna.rutkowska@uj.edu.pl.
authors: Joanna
authors: 0000-0003-0396-1790
authors: J
authors: Rutkowska
authors: Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, Kraków 30-387, Poland.
authors: Edyta T
authors: ET
authors: Sadowska
authors: Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, Kraków 30-387, Poland.
authors: Mariusz
authors: M
authors: Cichoń
authors: Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, Kraków 30-387, Poland.
authors: Ulf
authors: U
authors: Bauchinger
mesh_terms: D000818:Animals; D001823:Body Composition; D001835:Body Weight; D004734:Energy Metabolism; D005215:Fasting / Q000502:physiology*; D005247:Feeding Behavior / Q000502:physiology; D046369:Finches / Q000502:physiology*; D050356:Lipid Metabolism; D014867:Water; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D014867:Water
keywords: Body composition; Energy budget; Metabolic water; Protein sparing; Taeniopygia guttata