Fruits and vegetables can mitigate metabolic acidosis

Metabolic acidosis can commonly affect individuals with CKD and is associated with higher levels of angiotensin II, a pathway that powerfully promotes hypertension, a decline in renal function, and irreversible fibrosis of kidney tissue. This condition is exacerbated by a diet rich in fat and animal proteins, which generate a higher acid load than impaired kidneys can handle. Current clinical guidelines indicate alkali therapy for severe (<22 mM PTCO2) but not for milder (22–24 mM PTCO2) cases. To determine if patients with stage 3 CKD and less severe metabolic acidosis could also benefit from therapy, Nimrit Goraya, MD, of the Texas A&M College of Medicine and her co-workers investigated if adding fruits and vegetables (which generate a net alkaline load) or oral doses of sodium bicarbonate could reduce the decline in kidney function.

Building on their previous research, they performed a prospective trial with 108 patients receiving antihypertensive medications and who were randomized to receive fruits and vegetables, oral sodium bicarbonate, or neither (control) for a period of 3 years. At the conclusion of the study, both the fruits and vegetables group and the oral bicarbonate group demonstrated significantly better outcomes in mean systolic blood pressure, urine angiotensinogen (a biomarker for angiotensin II activity), and eGFR when compared to controls. The fruits and vegetables group had a larger, but statistically significant, reduction in eGFR decline and lower increase in systolic blood pressure than those receiving oral bicarbonates. Goraya added that her group’s other studies have demonstrated the benefits of fruits and vegetables for patients with stage 4 CKD as well. “Although you can’t make conclusions from a single randomized trial with a small population such as this one, the initial results look encouraging for those with mild metabolic acidosis,” said Brosius.

Goraya noted further benefits to those who received fruits and vegetables: a beneficial lifestyle change and weight loss. “They mainly received potatoes and raisins, which are relatively inexpensive, and it was easy for the participants to follow the diet and incorporate these changes.” The potato is the most alkali vegetable, and raisins, apples, and berries also have high alkali levels, she added. The study’s benefits weren’t limited to study participants because of a novel intervention mechanism: individuals received their fruits and vegetables at a local food bank and were provided enough for their entire family. In addition, “patients were followed for risk of potassium increases at serial 4 weekly intervals and no additional hyperkalemia risk was noted,” she said. Of note, the study population excluded diabetics and patients with potassium >4.6 mEq/L at baseline.

Can improved nutrition help reduce the effects of health disparities in these at-risk populations for developing CKD? Brosius says that these studies suggest that it might. “The implication of these studies, which have yet to be validated by other studies, is that the kind of diet that these studies recommend—high in fruits and vegetables and lower in animal protein and fat and lower in sodium—will in the long run have a significant impact on the outcome of patients who are at highest risk and live in poverty situations, and will mitigate some of that risk.”

Brosius cautions that physicians need to be aware of potassium levels, to ensure they don’t become elevated in patients with CKD, especially. “These are high-potassium diets and that’s the only risk associated with them, although it is a relatively modest one. These studies suggest that nutrition could possibly help in ameliorating the disparities in health care that individuals in poverty face,” which he concludes is “potentially a very positive low-cost intervention that may help long-term outcomes.”

December 2012 (Vol. 4, Number 12)