In the United States, approximately 80% of non-dialysis dependent CKD (NDDCKD) patients have hypertension. Reducing hypertension in these patients can lead to a slower decline in glomerular filtration rate (GFR), lower albumin excretion rate, and a lower risk of cardiovascular events (Semin Nephrol. 2005;25:435-439) and, hypothetically, better outcomes.
The National Kidney Foundation Clinical Practice Guidelines for Hypertension recommend a BP of 130/80 mm Hg for NDDCKD patients. Hypertension treatment typically includes the use of diuretics, ACE inhibitors, and/or angiotensin receptor blockers to lower BP and block the renin-angiotensin-aldosterone pathway.
A well known adverse effect of these treatments is an increased risk of hyperkalemia (serum potassium above 5.5 mEq/L). A study of non-diabetic NDDCKD patients by Weinberg et al (Arch Intern Med. 2009;169:1587-1594) found an association between GFR and hyperkalemia risk. Hyperkalemia was 5.4 times as likely to occur in patients with a GFR less than 40 mL/min/1.73m2 than in those with a GFR greater than 50.
The Dietary Approaches to Stop Hypertension (DASH) diet is a nonpharmacological intervention for hypertension. Originally, the DASH study, a multicenter, randomized control trial, was conducted as a feeding study in a population at high risk for hypertension.
This study provided all the food to study participants and had less emphasis on behavioral modification.The results demonstrated significantly lower systolic and diastolic pressure in the treatment group by 5.5 and 3.0 mm Hg, respectively (N Engl J Med. 1997;336:1117-1124). The intervention diet was designed to determine whether a combination of nutrients could be an effective treatment for hypertension. This feeding study was followed up by both the DASH-Sodium trial and the PREMIER trial.
As stated, the DASH Dietary Pattern was designed to combine nutrients believed to lower BP pressure and minimize nutrients felt to contribute to it. Thus, it is high in calcium, potassium, magnesium, and fiber, and lower in fat, especially saturated fat, and protein. The DASH-Sodium diet also limits sodium intake.
The DASH-Sodium trial randomly assigned participants to either a control diet or the DASH diet. Then within each group, the subjects followed consecutively lower sodium diets for 30 days. The results of this demonstrated that lowing dietary sodium in both groups resulted in significantly lower blood pressure (N Engl J Med. 2001;344:3-10).
The PREMIER study was designed to compare the effects of lifestyle behavior interventions, the DASH diet against the Joint National Committee-V clinical practice guidelines (Ann Epidemiol. 2003;13:462–471), again the DASH diet resulted in significantly lower BP.
In the PREMIER trial, Appel et al. randomized 810 health adults with untreated prehypertension or stage 1 hypertension to one of three intervention groups, including an “advice-only” group, an “established” group in which subjects followed established lifestyle recommendations for BP control (e.g., sodium reduction, weight loss, and increased physical activity), or an “established-plus-DASH” group that used established lifestyle recommendations with the DASH diet.
Compared with the advice-only group, the established and established-plus-DASH group had a 14% and 12% reduction in the 10-year estimated coronary heart disease risk (Circulation. 2009;2026-2031).
CKD and DASH
Using the DASH diet with patients who are in the early stages of CKD (stages 1 and 2) would be ideal. This diet would promote low BP, reduce sodium intake, and may reduce cardiovascular risk factors such as high BMI and hyperlipidemia, with little risk of hyperkalemia. However, as patients progress to stage 3 and a GFR below 50, is the DASH diet still ideal?
At this writing, I could find no published clinical trials testing the safety or efficacy of the DASH diet in patients with CKD. The concept has been explored, however. Lindley (Semin Dial. 2009;22: 260-263) suggests the DASH-sodium diet is appropriate for use in hemodialysis patients with the caveat that patients need to avoid salt substitutes due to their elevated potassium concentrations. Others such as Thoms (CANNT J.2005;15-2:58-59) suggest that the original DASH is not appropriate for CKD patients, but the DASH-sodium trial is important because it shows that sodium reduction alone can reduce hypertension.
I would suggest that data from the DASH, DASH-sodium, and the PREMIER trial indicate that the combined nutrient concept originally proposed by Appel et al. has proven to be successful. Sodium reduction alone does not offer the CKD patient optimal benefit due to a combination of nutrients such as that provided by the DASH diet.
Therefore, a hypothetical alternative to a single reduction in sodium that could be implemented safely in NDDCKD patients might be a modified DASH diet—one that uses lower-potassium fruits and vegetables and includes close monitoring of serum potassium, parathyroid hormone, and phosphorus.
This has not been studied, however, so clinicians must independently decide if the DASH diet is appropriate for their CKD patients and if close monitoring of serum parameters in possible. In conclusion, the DASH diet and its combined nutrient theory hold great potential as an economical dietary intervention for future studies in the CKD population.