The presence of protein in urine indicates a disruption in the function of the renal glomeruli or tubules, through which blood filtration and reabsorption of necessary substances occur.
When doctors detect protein in urine, they often recommend limiting protein intake in the diet. The logic behind this approach is to reduce the load on the kidneys, as excess protein increases the volume of filtration and may exacerbate nephron damage.
However, limiting protein may disrupt physiological processes of recovery and absorption, particularly endocytosis—a cellular mechanism through which tubular cells "capture" proteins that have leaked into the primary urine and return them to the bloodstream.
Why you shouldn't reduce protein intake
Endocytosis and protein reabsorption. Normally, a small amount of protein still passes through the filtration barrier in the renal glomeruli. These molecules are then captured by proximal tubular cells through receptor-mediated endocytosis (for example, via megalin and cubilin receptors). If this process is disrupted (for instance, due to a lack of protein in the diet), the recovery of leaks will worsen, and protein will continue to be lost in urine.
Nephrons and protein deficiency. Nephrons—the functional units of the kidneys—require protein for the synthesis of enzymes, transport proteins, and receptors. When protein intake is limited, tubular atrophy may begin, further reducing their ability to reabsorb proteins and increasing proteinuria.
The paradox of low-protein diets. In the short term, reducing protein may slightly lower the level of proteinuria. But in the long term, cell regeneration worsens, transport and endocytosis activity decreases, and protein loss in urine may only increase.
Why the right treatment is protein and phospholipids
Phospholipids for tubular membranes. Phospholipids are key building blocks of cell membranes, especially in the epithelium of the proximal tubules of the kidneys, where the main process of protein endocytosis occurs. Their deficiency disrupts membrane recovery and structure, reduces receptor mobility (for example, megalin and cubilin), and hinders protein capture and utilization.
Foods rich in phospholipids (especially eggs, caviar, liver, and sea fish) improve the regeneration of renal epithelium and support reabsorption processes.
Proteins as substrates for recovery and detoxification. Proteins are necessary not only for systemic support but also for local recovery of tubules, synthesis of enzymes, transport proteins, and receptor restoration.
In cases of protein deficiency (especially albumin), the body begins to utilize internal reserves (muscle and organ proteins), which exacerbates catabolism and increases protein excretion through urine.
