Which food source mainly provides urea filtered from the blood by the kidneys?

The primary source of urea in the blood, which the kidneys filter, comes from protein metabolism. When proteins are digested and broken down, they produce ammonia, which the liver then converts into urea, a less toxic compound. This process occurs predominantly after consuming animal proteins found in meat and certain plant-based products like legumes, which are also rich in proteins.

Meat, being a high-protein food, significantly contributes to the levels of urea in the bloodstream due to the breakdown of amino acids. Legumes, while plant-based, are also notable for their protein content and thus play a role in urea production when consumed. This understanding highlights the connection between the diet, protein intake, and the regulation of nitrogenous waste like urea filtered by the kidneys.

Other food sources listed, such as fruits, grain products, and fats like lard and oils, are either low in protein content or do not contribute to urea production in the same way, leading to a lower impact on the levels of urea in the bloodstream.