Diet and the Kidney: Studies Examine Effects of Sugar-Sweetened Beverages and Fruit and Vegetable Consumption

New studies point to the importance of diet for kidney health in the general population as well as for the longevity of patients on dialysis. The studies, which are both published in the Clinical Journal of the American Society of Nephrology (CJASN), suggest that more research is needed to fine-tune certain dietary recommendations.

The first study, by Casey Rebholz, PhD, MPH, of the Johns Hopkins Bloomberg School of Public Health, and her colleagues, was conducted to clarify the effects of certain beverages on kidney health.

“There is a lack of comprehensive information on the health implications of the wide range of beverage options that are available in the food supply,” Rebholz said. “In particular, there is limited information on which types of beverages and patterns of beverages are associated with kidney disease risk in particular.”

Of note, the study focused on African Americans, who experience a disproportionate burden of kidney disease but are under-represented in clinical research. The team prospectively studied 3003 African American men and women with normal kidney function who were enrolled in the Jackson Heart Study.

Participants completed a food frequency questionnaire administered at the start of the study in 2000–2004, and they were followed until 2009–2013. Among the 3003 participants, 185 (6%) developed chronic kidney disease (CKD) over a median follow-up of 8 years. After adjustment for confounding factors, consuming a beverage pattern consisting of soda, sweetened fruit drinks, and water was associated with a higher risk of developing CKD. Participants in the top tertile for consumption of this beverage pattern were 61% more likely to develop CKD than those in the bottom tertile.

It was surprising that water was a component of the beverage pattern that was linked with a higher risk of CKD, although study participants may have reported their consumption of a wide variety of types of water, including flavored and sweetened water. The investigators did not collect information about specific brands or types of bottled water in the Jackson Heart Study.

In an accompanying editorial, Holly Kramer, MD, MPH, and David Shoham, PhD, of Loyola University Chicago, noted that the findings hold strong public health implications. “Although a few cities in the United States have reduced sugar-sweetened beverage consumption via taxation, most municipalities have resisted public health efforts to lower its consumption,” they wrote. “This cultural resistance to reducing sugar-sweetened beverage consumption can be compared with the cultural resistance to smoking cessation during the 1960s after the Surgeon General report was released. During the 1960s, tobacco use was viewed as a social choice and not a medical or social public health problem.”

In an accompanying Patient Voice editorial, Duane Sunwold said he is a patient with CKD who changed his eating and drinking patterns to put his disease in remission. As a chef, he offers a number of recommendations to fellow patients trying to decrease their consumption of sugar-sweetened drinks.

Balancing fruit, vegetable intake and kidney failure

The second CJASN study examined the effects of fruit and vegetable intake in patients undergoing maintenance hemodialysis. Although higher fruit and vegetable intake is linked with lower cardiovascular and all-cause mortality in the general population and lower all-cause mortality among patients with mild to moderate CKD, kidney failure patients on hemodialysis are often discouraged from this type of diet due to its potential to cause a buildup of potassium and the development of hyperkalemia.

“Although diet is a key component of self-management and provides an important opportunity for a collaborative approach between patients and healthcare professionals to improve care, there is limited evidence on the impact of diet on patient-relevant outcomes,” said lead author Valeria Saglimbene, MScMed, of the University of Sydney School of Public Health, in Australia.

In the study of 8078 hemodialysis patients who completed food frequency questionnaires, only 4% of patients consumed at least 4 servings of fruits and vegetables per day as recommended in the general population. The investigators noted that there were 2082 deaths (954 from cardiovascular causes) over a median follow-up of 2.7 years. Compared with patients who had 0–5.5 servings of combined fruits and vegetables per week, those who had 5.6–10 servings and those who had more than 10 servings had 10% and 20% lower risks of dying from any cause, respectively, as well as 12% and 23% lower risks of dying from non-cardiovascular causes.

“These findings suggest that well-meaning guidance to limit fruit and vegetable intake to prevent higher dietary potassium load may deprive hemodialysis patients of the potential benefits of these foods; however, intervention trials of fruit and vegetable intake are needed to support dietary recommendations for hemodialysis patients,” said co-author Germaine Wong, MBBS, PhD, also of the University of Sydney School of Public Health. “Future studies exploring the potential benefits of a whole dietary approach in the hemodialysis setting are also warranted and we aim to pursue them,” added senior author Giovanni Strippoli, MD, PhD, of Diaverum AB, in Sweden and the University of Bari, in Italy.

In an accompanying editorial, Ranjani Moorthi, MD, of Indiana University noted that the findings may spur future studies. “The hope is this excellent cohort study will form the basis of well-designed randomized controlled trials to test the effects of fruits and vegetables in patients undergoing hemodialysis, so we, their nephrologists, along with renal dietitians, can provide the details of dietary guidance they deserve.”

February 2019 (Vol. 11, Number 2)