Which one among the following substances is never excreted out through urine under normal circumstances in any healthy individual?

In a healthy individual, the kidneys function to filter blood and remove waste while conserving essential nutrients. Urine is primarily composed of water and solutes like urea, which is the main nitrogenous waste product [1]. Electrolytes such as sodium and potassium are also normally excreted in varying amounts depending on dietary intake and physical activity to maintain homeostasis [1]. While amino acids are filtered at the glomerulus, they are considered essential organic solutes for body metabolism. Under normal circumstances, the proximal tubules of the nephron perform highly efficient reabsorption, ensuring that virtually 100% of filtered amino acids are returned to the bloodstream [2]. Consequently, only negligible or trace amounts are present in the final urine of a healthy person [2]. The presence of significant amino acids in urine, known as aminoaciduria, typically indicates renal tubular defects or metabolic disorders [2].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > 5.5.1 Excretion in Human Beings > p. 96
2. [2] https://pmc.ncbi.nlm.nih.gov/articles/PMC7153418/