In humans, urea is mainly formed from the metabolism of which one of the following components of food?

In humans, urea is the primary nitrogenous waste product formed during the metabolism of proteins and their building blocks, amino acids [2]. Unlike carbohydrates and lipids, the body has no dedicated storage form for excess amino acids. When amino acids are catabolized, the first step involves deamination—the removal of the amino (NH2) group—which results in the formation of ammonia. Because free ammonia is highly toxic to human tissues, it is transported to the liver, where it enters the urea cycle. This biochemical pathway converts toxic ammonia into urea, a neutral and water-soluble compound that can be safely transported in the blood and excreted by the kidneys [2]. While glucose and fatty acids serve as major fuel sources, they do not contain nitrogen and thus do not contribute to urea formation [1].

Sources

1. [2] https://www.ncbi.nlm.nih.gov/books/NBK513323/
2. [1] https://www.sciencedirect.com/topics/medicine-and-dentistry/protein-metabolism