Dietary protein intake and long-term outcomes after kidney transplantation

For kidney transplant recipients (KTR), optimal dietary protein quantity and quality is unknown. In this thesis, we aimed to investigate several aspects of protein intake after kidney transplantation and their associations with long-term outcomes. Through observational, prospective cohort studies, we found that higher protein intake was associated with longer patient and graft survival compared to low protein intake, likely through a multifactorial pathway that includes preservation of muscle mass and physical fitness. A relatively high urinary excretion of markers for white and red meat intake was found to be associated with lower risk of long-term graft failure. Protein intake provides amino acids as building blocks, but also amino acids that can be used as substrate for production of other molecules, including nitric oxide (NO) and hydrogen sulfide (H2S). We found that high urinary excretions of metabolites of NO and of H2S were respectively associated with longer patient and graft survival. Another compound that can originate from dietary protein, or is produced during endogenous protein turnover, is asymmetric dimethylarginine, of which we found that higher urinary excretion was associated with longer patient survival. Although observational in nature, the results of this thesis strongly suggest that KTR should not be subjected to a low protein intake and that a relatively high protein intake is advantageous for long-term survival. Therefore, we call for an intervention study to investigate the effect of protein intake in KTR on long-term outcomes, in order to determine the optimal quantity and quality of dietary protein intake in KTR