Mediterranean Diet May Help Preserve Kidney Function

A Mediterranean diet may be beneficial for not only heart health, but kidney health as well. This is the conclusion of a new long-term study presented at Kidney Week 2013 that found individuals following a regimen similar to a Mediterranean diet reduced their risk for developing chronic kidney disease (CKD) and for rapid decline in kidney function. Although the diet’s heart health benefits have received public attention, it has been unknown if this diet confers any nephroprotective effects. Because of the close connection between cardiovascular and kidney disease, Minesh Khatri, MD, and his coworkers from Columbia University theorized a Mediterranean diet may have a positive effect on preserving renal function.

They examined the multiethnic Northern Manhattan Study cohort, a prospective, long-term, multiethnic cohort of 3298 residents of Upper Manhattan. Each participant underwent a baseline screening and was followed up annually by phone. Khatri isolated a subset of 900 individuals who underwent subsequent laboratory testing approximately 7 years later. Adherence to a diet similar to a Mediterranean diet (higher in vegetables, fruit, unrefined whole grains, and lower in meat and dairy products than a traditional Western diet) was scored using the 9-point MeDi system.

In contrast to the DASH (Dietary Approaches to Stop Hypertension) diet—which limits sodium intake to less than 2300 mg (or in some case 1500 mg) per day—the Mediterranean diet has more of an emphasis on the so-called “heart-healthy” monounsaturated fats (such as those found in olive oil and nuts) as well as a moderate intake of wine, said Khatri.

Their analysis looked at two outcomes: a primary outcome of incident stage III CKD, and a secondary outcome of rapid kidney function decline. The observational, longitudinal study of 900 mostly older participants in New York demonstrated that participants who were consuming a Mediterranean diet at a level above the median for this cohort had a 50 percent reduced risk for incident CKD, and a 42 percent reduced risk of rapid kidney function decline (greater than 2.5 mL/min/1.73 m2/year) over the course of the 7-year follow-up period.

“There were no interactions between the Mediterranean diet and age, race-ethnicity, BMI, or hypertension,” Khatri said. “However, increased vegetable intake may have been driving the benefit as that individually was one component of the Mediterranean diet that was significantly associated with reduced risk of incident CKD.”

The study results appear to be consistent with a number of recently published studies on diet and kidney disease, said Lauren Graf, MS, RD, a renal dietician at Montefiore Medical Center who was not affiliated with the study.

“A Mediterranean diet is higher in vegetables, fruit, and unrefined whole grains, and lower in meat and dairy products compared to a traditional Western diet,” Graf said. “The benefits of a Mediterranean diet over a standard American diet are multifactorial. The lower animal protein content of the Mediterranean diet puts less stress on the kidneys and reduces the acid load on the body. The diet is also higher in fiber and antioxidants, which has been shown to reduce inflammation and mortality. One study found these benefits to be even more profound in patients with CKD than in those without.”

“Since observational studies like this have limited ability to detect causality, the next research step would be to have a controlled clinical trial where subjects are randomized to receiving a Mediterranean diet versus a controlled diet,” Khatri said. “In the future, observational studies should focus on the effect of a Mediterranean diet in subjects with advanced CKD. Our study was in a cohort of people with relatively well-preserved kidney function. Larger, longitudinal studies in other populations would also add useful information. Ultimately, however, randomized control trials are needed to definitively prove whether a Mediterranean diet significantly impacts kidney function.”

Asked whether physicians should recommend the diet for their patients, Khatri said clinicians and patients should understand that this is an observational study.

“We cannot draw firm conclusions that the Mediterranean diet is beneficial for either kidney disease prevention or progression,” he said. “Further research is needed before we can universally recommend this approach for kidney disease patients. However, there is substantial data that the Mediterranean diet may be beneficial for prevention of heart disease (2). Given the close relationship between salt intake and hypertension, I would probably modify the Mediterranean diet to limit sodium intake to less than 2.3 g per day, which is part of the DASH diet. I think among people with preexisting advanced kidney disease, factors such as serum potassium and phosphate levels would need to be considered, and the diet should be individualized with input from a nutritionist.”

Graf also cautions people do not always understand what the Mediterranean diet is and what aspects of the diet are beneficial. “One misconception is that people often think the health benefits of a Mediterranean diet are mainly from olive oil,” she said. “The real benefits of the diet come from higher intake of vegetables, fruit, nuts, beans, and other high fiber foods and also from minimal intake of red meat and processed foods.”

References

1. 

Khatri M, et al. The Impact of a Mediterranean Style Diet on Kidney Function. J Am Soc Nephrol 2013; 24 (Suppl):83A (Abstract)

2. 

Estruch R, et al. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med 2013; 368:1279–1290.