Kidney and bladder health

08 February 2013

Fruit and veg reduce metabolic acidosis

Fruits and vegetables worked as well as sodium bicarbonate in reducing metabolic acidosis and kidney injury in a small study of patients with late-stage CKD.

Fruits and vegetables worked as well as sodium bicarbonate in reducing metabolic acidosis and kidney injury in a small study of patients with late-stage chronic kidney disease (CKD), researchers say.

The study suggests that sodium bicarbonate (NaHCO3) and fruits and vegetables "are comparable in their kidney-protective effect but much more study is required before we can make a definitive comparison," said Dr Donald Wesson from Texas A&M College of Medicine in Temple.

He noted that current guidelines recommend alkali treatment of metabolic acidosis in patients with reduced kidney function, "and we should do this unless there is a contraindication for doing so," he said. "Presently, many such patients are not treated and many of those who are (treated) are under treated."

"Our studies showing that dietary acid reduction with alkali (NaHCO3) and possibly fruits and vegetables can help protect kidneys reinforce this message" that metabolic acidosis should be treated, Dr Wesson said.

The 71 study patients had stage 4 CKD - that is, an estimated glomerular filtration rate (eGFR) 15-29 mL/min/1.73m2 - due to hypertensive nephropathy, plasma total CO2 (PTCO2) <22 mM, and were receiving angiotensin-converting enzyme (ACE) inhibitors.

As reported online in the Clinical Journal of the American Society of Nephrology, 35 patients were randomly assigned to one year of daily oral NaHCO3 at 1.0 mEq/kg/day and 36 to base-producing fruits and vegetables, which the team found in a 2011 study would reduce dietary acid by half.

The fruits and vegetables were provided free of charge and prescribed by a dietitian. Individuals were not given specific dietary instructions, and they integrated the prescribed fruits and vegetables into their diets as they wished.

'Limited impact on clinical practice'

The researchers report that kidney function was similar in the two groups at baseline and at one year; that is, base-producing fruits and vegetables or oral NaHCO3 yielded similar eGFRs at one year.

PTCO2 increased in both groups over baseline (p<0.01), consistent with a lessening of metabolic acidosis, and was higher in the NaHCO3 group at one year (p<0.001). Urinary indices of kidney injury were also lower at one year in both groups.

"The data support fruits and vegetables as an effective alternative to Na+-based alkali to improve metabolic acidosis and reduce kidney injury in stage 4 CKD and suggest that fruits and vegetables be studied further as a potential kidney-protective adjunct to blood pressure reduction and ACE inhibition in hypertensive nephropathy," the authors say in their paper.

Dr Wesson said it's important to "recognise that these are small-scale studies and larger ones will be needed, and done by other labs to confirm our findings, before we can make general recommendations to clinicians."

In the current study, plasma potassium concentration did not increase in either group. But Dr Wesson said, "For now, clinicians should use caution in treating CKD patients with fruits and vegetables because the associated high potassium load can induce life-threatening potassium toxicity in kidney patients who commonly have reduced ability to excrete administered potassium."

In an editorial, Dr Muhammad Yaqoob of Barts Health NHS Trust and William Harvey Research Institute in London, UK notes that the study is likely to have a limited impact on clinical practice.

"A small group of highly motivated patients wishing to reduce their pill burden through dietary modification may benefit from the results of this study. However, many patients find it difficult to follow a diet high in fruits and vegetables and might therefore be more adherent to a supplement," he wrote.

Dr Yagoob says a large multicenter randomised controlled trial examining the impact of supplemental bicarbonate, with and without dietary intervention, in patients with chronic kidney disease is needed.

The study had no commercial funding and the authors had no conflicts of interest to disclose.

(Reuters Health, February 2013)

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