Objective: Metabolic acidosis and the uremic toxins, indoxyl sulphate (IS) and p-cresyl sulphate (PCS), are associated with increased risks of kidney disease progression, muscle catabolism, cardiovascular disease, and mortality in patients with chronic kidney disease (CKD). The New Nordic Renal Diet (NNRD) is a plant focused meal pattern, with reduced phosphorus and protein content compared to an average Danish diet. Due to a higher amount of plant-based products, we hypothesized that NNRD would reduce renal excretion of acids and uremic toxins. Thus, we evaluated the effects of NNRD on metabolic acidosis and uremic toxins in patients with moderate CKD, stages 3-4.

Design and methods: This post hoc analysis is based on a randomized controlled crossover trial comparing 1-week of the NNRD to a control period of an average Danish diet with a 1-week period, in patients with CKD stages 3 and 4. Urine pH and urine excretion of bicarbonate, ammonium, titratable acids, IS and PCS alongside plasma total CO₂ (tCO₂) were measured at days 1, 4, and 7 in 18 patients.

Results: After 7 days on NNRD 24-h urine net acid excretion (NAE) was decreased by 80% (P<.001), 24-h urine excretion of ammonium and bicarbonate decreased by 34% (P<.001) and increased by 678% (P<.001), respectively, compared with the control period. Plasma tCO₂ was increased by 8% (P=.005). Moreover, 24-hour urine excretion of PCS and IS were reduced by 31% (P=.018) and 29% (P<.001), respectively.

Conclusion: One week of NNRD in patients suffering from moderate CKD effectively improved metabolic acidosis with a marked reduction in urine NAE that included a large increase in urine bicarbonate excretion. In addition, NNRD reduced urinary excretion of the uremic toxins PCS and IS. These results encourage further investigations of the long-term effects of NNRD on renal protection in patients with CKD.