Dietary Acid Load and Metabolic Acidosis in Renal Transplant Recipients

Background and objectives Acidosis is prevalent among renal transplant recipients (RTRs) and adversely affects cardiometabolic processes. Factors contributing to acidosis are graft dysfunction and immunosuppressive drugs. Little is known about the potential influence of diet on acidosis in RTRs. This study examined the association of metabolic acid load with acidosis and with cardiovascular risk factors in RTRs and aimed to identify dietary factors associated with acidosis. Design, participants, setting, & measurements 707 RTRs were included. Metabolic acid load was assessed by measuring 24-hour urinary net acid excretion (NAE; i.e., titratable acid + ammonium - bicarbonate). Acidosis was defined as serum [HCO3-] < 24 mmol/L. BP and insulin resistance, reflected by hemoglobin A1c, were among cardiovascular risk factors. Diet was assessed with food-frequency questionnaires. Linear regression analysis was applied to investigate association between NAE and acidosis and between dietary factors and acidosis. Results Mean age +/- SD was 53 +/- 13 years; 57% of patients were male. Acidosis was present in 31% of RTRs. NAE was associated with acidosis (serum HCO3-: beta=-0.61; serum pH: beta=-0.010; both P<0.001). Patients with high intake of animal protein (i.e., from meat, cheese, and fish) and low intake of fruits and vegetables had significantly lower serum HCO3- and serum pH. No associations were observed between NAE and cardiovascular risk factors, such as hypertension and insulin resistance. Conclusions In addition to conventional factors contributing to acidosis, diet might influence acid-base homeostasis in RTRs. Higher intake of fruits and vegetables and lower animal protein intake is associated with less acidosis in RTRs. J Am Soc Nephrol 7: 1811-1818, 2012. doi: 10.2215/CJN.04590512