ASN 2010: The DASH Diet, Cardiovascular Health, and Patients with CKD

A leading researcher in the mitigation of cardiovascular hypertension risk laments the fact that so few traditional recommendations for dietary and lifestyle changes aimed at managing the complication are quantified by studies reporting hard outcomes.

Nevertheless, cohort-based research and other evidence does validate some of the more recent dietary suggestions that apply to chronic kidney disease (CKD) patients, as well as other cardiovascular patients, Lawrence Appel, MD, told colleagues at the American Society of Nephrology 43rd Annual Meeting and Scientific Exposition.

Appel, a professor at Johns Hopkins University in Baltimore, MD, is among the researchers participating in continuing studies related to Dietery Approaches to Stop Hypertension (DASH) -- a project that added a dietary component to long-held recommendations for at-risk heart patients to lower their sodium, lose weight, exercise regularly, and limit alcohol intake. The DASH diet was borne of an eight-week study that compared it to a control diet and a fruit-and-vegetable diet. The DASH diet incorporates all of the American Heart Association dietary recommendations.

There are now at least nine cohort studies that validate the DASH suggestions for sodium, saturated fat, protein, and other dietary intakes, Appel said. One of these is the Nurse’s Health Study, which compiled data from 238,000 nurse participants and showed that increased adherence to the DASH diet correlated with reduced risk for stroke. Outcomes from the study also gave credence to several other DASH recommendations.

Appel wasn’t at the ASN conference to challenge recommendations that have long been endorsed by the American Heart Association. However, he said that traditionally-held beliefs related to heart disease management haven’t earned the same degree of scientific confirmation from the research community as DASH has, when quantifiable hard outcomes or even surrogate outcomes are used as the yardstick.

“For smoking cessation, really, you don’t really have trials for surrogate (outcomes). It’s really based on observational, studies, and that is what drove evidence and policymaking,” Appel said. “Weight reduction is the same thing: We don’t have any clinical trials in the general population with hard outcomes. There’s one ongoing now, but it’s in diabetics. The same thing is true for sodium reduction -- no trial with hard outcomes. It really is based primarily on studies or trials with blood pressure. For potassium, the evidence is a bit weaker and is based on observational studies.”

Appel pointed out that some data-related caveats do exist. For instance, DASH recommendations for heart patients, and by extension CKD patients, are not all that different than recommendations promulgated for the general population. Moreover, some of the data seem to be leading researchers in cryptic directions. One area that can be categorized this way is potassium intake. For CKD patients at stages one or two, the recommendation is greater than 4,000 mg daily. For those at stages three and four it falls in at between 2,000 and 4,000 mg daily. The recommendation for potassium in the general population is 4,700 mg.

“Quite frankly, there’s really not a lot of data, and I think the question is really out there: ‘Is it a friend; is it a foe, or could it be both?’ I think it’s bi-directional: It’s beneficial in patients with less advanced CKD; and, possibly, it’s harmful in patients with advanced CKD. And we don’t know where the tipping point is,” Appel said.