Urea is produced by metabolism of

Urea is the primary nitrogenous waste product in mammals, produced specifically through the metabolism of proteins. When proteins are catabolized, they are broken down into amino acids, which then undergo deamination to remove the amino group [2]. This process releases ammonia, a highly toxic substance that must be neutralized. The liver converts this ammonia, along with carbon dioxide, into urea via the urea cycle [3]. While carbohydrates and lipids are major energy sources, they consist primarily of carbon, hydrogen, and oxygen, and do not contain the nitrogen required to form urea. In contrast, nitrogen is an essential constituent of proteins. The resulting urea is transported through the blood to the kidneys for excretion in urine. Therefore, urea production is a direct consequence of protein (amino acid) degradation rather than carbohydrate or lipid metabolism.

Sources

1. [2] https://www.ncbi.nlm.nih.gov/books/NBK541039/
2. [1] https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/protein-metabolism
3. [3] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Nitrogen (N) > p. 363