Adding fruits and vegetables to the diet may help protect the kidneys of patients with stage 4 chronic kidney disease (CKD) with too much acid build-up in their blood. Western diets composed largely of animal and grain products are highly acidic and can lead to metabolic acidosis. As kidney disease progresses the ability of CKD patients to get rid of this excessive dietary acid through the urine declines. Metabolic acidosis can cause rapid breathing, confusion, and lethargy. Severe cases can lead to shock or death.
Alkali supplementation therapy (such as with sodium bicarbonate) is used to treat CKD patients with severe metabolic acidosis, but simply adding more fruits and vegetables -- with their high alkali residue -- may be a better alternative than sodium bicarbonate, since those with stage 4 CKD may have trouble getting rid of the excessive sodium load too. On the other hand, the ability of those with advanced CKD to get rid of dietary potassium is also reduced, which could lead to a dangerous elevation of serum potassium levels.
Dr. Goraya and her colleagues tested the efficacy of adding either more fruits and vegetables or sodium bicarbonate to a group of 71 stage 4 CKD patients. The researchers randomly assigned the subjects to receive either added fruits and vegetables or an oral sodium bicarbonate medication for one year. Both treatments were designed to cut the dietary acid load in half.
After one year, kidney function in the two groups was similar. One-year plasma total carbon dioxide (PTCO2) increased in both groups, indicating a lessening of metabolic acidosis. However, PTCO2 was higher in patients receiving the bicarbonate medication than in those receiving added fruits and vegetables, perhaps because compliance was not as good. Urine measurements of kidney injury were lower after one year in both groups. Perhaps surprisingly, the increased fruits and vegetables (with their high potassium content) did not raise blood potassium to dangerous levels and serum potassium levels did not increase in either group.
Dr. Wesson noted: "We showed that by addition of alkali such as bicarbonate or alkali-inducing fruits and vegetables, patients had a favorable response by reduction of urinary kidney injury markers.” Dr. Goya added that: "Our study suggests that these interventions will help maintain kidney health in those with kidney disease."
Bottom Line: One year of increased fruits and vegetables or sodium bicarbonate medication in individuals with stage 4 CKD lowered urine indices of kidney injury. The data suggests that more fruits and vegetables can improve metabolic acidosis and reduce kidney injury even in stage 4 CKD without producing hyperkalemia. [Clinical Journal of the American Society of Nephrology, February 7, 2013,doi: 10.2215/ CJN.02430312].
The five stages of CKD and the GFR for each stage:
- Stage 1 with normal or high GFR (GFR > 90 ml/min)
- Stage 2 Mild CKD (GFR = 60-89 ml/min)
- Stage 3 Moderate CKD (GFR = 30-59 ml/min)
- Stage 4 Severe CKD (GFR = 15-29 ml/min)
- Stage 5 End Stage CKD (GFR <15 ml/min)
By James J. Kenney, PhD, FACN
Stephanie Ronco has been editing for Food and Health Communications since 2011. She graduated from Colorado College magna cum laude with distinction in Comparative Literature. She was elected a member of Phi Beta Kappa in 2008.