What is the main product of protein metabolism that is excreted in urine?

The primary product of protein metabolism that is excreted in urine is urea. When proteins are consumed, they are broken down into amino acids. These amino acids can be utilized for various bodily functions, including energy production and the synthesis of other compounds. However, when the body has more amino acids than it needs, or when proteins are metabolized, the nitrogen component of these amino acids must be removed. This process, known as deamination, results in the formation of ammonia, which is toxic in high concentrations.

The liver converts ammonia into urea through the urea cycle, making it less toxic and water-soluble, so that it can be easily excreted through the kidneys into the urine. Urea serves as a safe method for eliminating excess nitrogen from the body.

While amino acids and creatinine are also related to protein metabolism, they do not represent the main waste product excreted in urine. Amino acids can be directly used by the body or can be recycled, while creatinine is a breakdown product of creatine phosphate in muscle—its levels can indicate muscle mass and function but are not directly tied to protein metabolism like urea. Therefore, urea is the key product identified with nitrogen waste excretion in