Urea is a waste product produced by the liver during the metabolism of proteins. Metabolism refers to the chemical processes that occur within the cells of our body to break down substances and produce energy.

Option 1: Proteins - This option is correct. Proteins are made up of amino acids, and when proteins are metabolized, they are broken down into their constituent amino acids. One of the byproducts of this process is ammonia, which is then converted into urea by the liver. Urea is then excreted in the urine.

Option 2: Carbohydrates - This option is incorrect. Carbohydrates are broken down into glucose during metabolism. Glucose is then used as a source of energy or stored as glycogen. Carbohydrate metabolism does not directly produce urea.

Option 3: Lipids - This option is incorrect. Lipids, also known as fats, are broken down into glycerol and fatty acids during metabolism. This process does not produce urea.

Option 4: Both Proteins and Carbohydrates - This option is incorrect. While protein metabolism does produce urea, carbohydrate metabolism does not. Therefore, urea is not produced by the metabolism of both proteins and carbohydrates.

In conclusion, the correct answer