Plasma urea concentration is frequently up to 5-fold greater after a 5-day fast than after following a normal diet. This increase in urea concentration most likely reflects an increase in which of the following?

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Quizplus · Accepted Answer

During fasting, the body increases the breakdown of proteins to release amino acids, which are then used for gluconeogenesis in the liver. This process results in increased production of urea as a byproduct of amino acid catabolism.  Protein breakdown into constituent amino acids provides an important source of carbon for oxidative energy production. When amino acids are oxidized, the nitrogen is first transferred to a suitable α-keto acid acceptor such as α-ketoglutarate. Eventually the waste nitrogen from hepatic amino acid metabolism is diverted into the urea cycle for excretion in a nontoxic form. This accounts for the increased plasma urea concentrations following fasting.

Plasma Urea Concentration Is Frequently Up to 5-Fold Greater After