Nancy A. Melville
November 22, 2010 (Denver, Colorado) — The addition of fruits and vegetables to a diet can help offset acid imbalances and reduce the worsening of kidney disease among patients with hypertension, according to research presented here at Renal Week 2010: American Society of Nephrology 43rd Annual Meeting.
The study of 40 patients with hypertension-related kidney disease showed that the addition of fruits and vegetables over the course of 30 days resulted in significant improvements in the urine parameters of kidney injury.
Dr. Nimirit Goraya
According to lead author Nimirit Goraya, MD, from the Texas A&M College of Medicine, in Temple, acid retention is a known problem for patients with kidney disease, and the study was designed to address the issue with a dietary approach.
"We know that people with kidney injury have acid buildup in their body, and that giving things like sodium bicarbonate can slow down the progress of kidney decline, so we hypothesized that adding baseline-inducing fruits and vegetables could also reduce kidney injury in hypertensive patients," said Dr. Goraya.
"We showed that with just the addition of these fruits and vegetables, we were able to reduce kidney injury."
The participants included 40 patients in Texas, all with macroalbuminuric hypertension and estimated glomerular filtration rate (eGFR) levels of 60 to 90 mL/minute, in addition to 26 patients with eGFR levels greater than 90 mL/minute.
All of the participants had achieved blood pressure reduction with regimens including angiotensin-converting enzyme inhibition, Dr. Goraya said.
"In order to remove the concept of blood pressure as a variable in the outcome, we targeted patients with controlled blood pressure of 130/80."
The 2 groups showed no differences at baseline in potential renal acid load, a measure of dietary acid intake, and 8-hour urine net acid excretion (8h NAE).
Baseline potential renal acid load in eGFR levels of 60 to 90 mL/minute compared with eGFR levels higher than 90 mL/minute was 60.4 ± 19.4 vs 62.8 ± 14.5 mmol/day, respectively (P = .582). Baseline 8h NAE was 24.6 ± 5.0 vs. 24.7 ± 2.9 meq, respectively (P = .924) — measurements that were not different.
Patients were given a 30-day diet that added fruits and vegetables such as potatoes, raisins, grapes, apples, and other foods while avoiding some fruits and vegetables that were high in potassium.
At the end of the 30-day period, all patients showed reduced excretion of 3 key indicators of kidney injury: albumin, transforming growth factor β, and N-acetyl-β-D-glucosaminidase.
This dietary intervention in patients with eGFR levels of 60 to 90 mL/minute reduced urine excretion of albumin (422 ± 152 to 388 ± 122 mg/g creatinine [cr]; P < .0001), N-acetyl-β-D-glucosaminidase (2.68 ± 0.73 to 2.60 ± 0.70 U/g cr; P < .0001), and transforming growth factor β (63.8 ± 14.5 to 57.3 ± 13.7 ng/g cr; P < .0001), which is consistent with reduced kidney injury.
8h NAE in the patients with eGFR levels of 60 to 90 mL/minute was reduced from 24.6 ± 5.0 to 16.5 ± 5.1 meq (P < .0001).
"This was just a 30-day intervention, but we were able to show statistically significant reductions in these markers," Dr. Goraya said.
"The findings underscore that just this simple, inexpensive measure can make an enormous difference in helping our chronic kidney disease patients. Most of them do really listen to dietary changes because they don't want to add more and more medicines to their regimen."
The idea of health benefits from fruits and vegetables hardly represents a new approach, but the study does raise the important issue of a dietary approach over pharmaceuticals to help kidney disease patients, said Frank C. Brosius, MD, a professor of internal medicine in the University of Michigan's Department of Molecular and Integrative Physiology, in Ann Arbor.
"It certainly is not horribly surprising, given the data suggesting that acidosis can contribute to progression of disease, [and] it is certainly not clear that the positive results were actually due to the reduction in acid production and could be due to other salutary features of the fruit and veggie diet. This will need to be validated in long-term, larger studies where all controls are clearly in place.
"Nonetheless, it is a clearly nontoxic intervention that is likely to have a host of beneficial health effects," he added. "I think there is a nascent push to study and utilize nutritional interventions for all sorts of chronic diseases including kidney disease. This is partly driven by patient demand. The benefit of dietary interventions, if confirmed, would seem to be associated with favorable cost/benefit and risk/benefit ratios, especially when compared with pharmaceuticals."