Credit: Original article published here.
Chronic kidney disease (CKD) affects approximately 13% of the population of the United States. Many patients adhere to preventive dietary patterns; however, according to Shirin Pourafshar, PhD, MSCR, RDN, and colleagues, empiric evidence to guide use of such measures is limited. Current dietary guidelines for patients with CKD focus on recommended nutrient intakes (sodium, potassium, and phosphorous) rather than on whole foods such as fruits and vegetables.
Patients with CKD at risk for hyperkalemia limit intake of fruits and vegetables to avoid excess dietary potassium intake. Patients with mild-to-moderate CKD do not face a high risk of hyperkalemia, and restriction of dietary potassium may lower consumption of healthy foods such as fruits and vegetables. The 2000 update to the Clinical Practice Guideline for Nutrition in CKD from the National Kidney Foundation and the Academy of Nutrition and Dietetics includes the need for further evidence on food patterns and intake of fruits and vegetables in patients with CKD.
Dr. Pourafshar et al conducted a study to examine the relationship between CKD and intake of fruits and vegetables in US adults with and without CKD. Results were reported in the Journal of Renal Nutrition [2023;33(1):88-96].
The researchers characterized patterns of fruit and vegetable intake in participants in the National Health and Nutrition Examination Survey (NHANES) to assess similarities or differences between those with and those without CKD. The primary outcome of interest was patterns of fruit and vegetable intake based on participant self-reported dietary intake.
The study included three cohorts: NHANES III (1988-1994); Continuous NHANES cycle 2003-2010; and Continuous NHANES cycle 2011-20218. Patterns of fruit and vegetable intake were assessed using latent class analysis; weighted multinational logistic regression was used to compare intake patterns across the three temporal cohorts. Data from adults 18 years of age or older with complete, valid dietary recall data in each of the three NHANES cycles were analyzed.
The primary diet assessment method in NHANES was 24-hour dietary recall interview. In NHANES III one recall per participant was conducted; two recalls were performed in Continuous NHANES. Following general principles in the NOVA food classification system, foods were categorized into (1) unprocessed, (2) minimally processed, (3) and ultra-processed fruits and vegetables. Each fruit and vegetable was also classified by phytochemical content, resulting in four groupings: glucosinolate-rich; carotenoid-rich; polyphenol-rich; and starchy vegetable.
The percentage of the population with CKD across the years ranged from 13.6% (NHANES III) to 15.2% (Continuous NHANES 2011-2018). When CKD was defined by estimated glomerular filtration rate <60 mL/min/1.73 m2 only (stage G3a or higher), 6.5% in NHANES III, 6.6% in Continuous NHANES 2003-2010, and 6.9% in Continuous NHANES 2011-2018 would have CKD, indicating a large proportion with albuminuria only, particularly in later cohorts.
Among the CKD population, average age was 58.5 years compared with 41.0 years among non-CKD participants in NHANES III; 60.3 years and 43.4 years in Continuous NHANES 2003-2010; and 60.0 years and 44.6 years in Continuous NHANES 2011-2018. In all three cohorts, participants with CKD were likely to be older, female, and Black, and to have higher body mass index, hypertension, and diabetes compared with participants without CKD.
In all three cohorts, total energy intake was significantly higher among participants without CKD compared with those with CKD. In NHANES III and Continuous NHANES 2003-2010, the percentage of calories from protein (P<.001 and P=.007, respectively) and carbohydrate (P=.005 and P<.001, respectively) was significantly higher in those with CKD. Unadjusted macronutrient densities of fiber, phosphorus, sodium, and potassium, but not dietary carotenoids, were higher in those with CKD in most cycles.
Within the three datasets, the researchers identified one pattern of overall low consumption of fruits and vegetables (overall low intake), one pattern with higher intake of unprocessed fruits and vegetables in all phytonutrient categories (high unprocessed), one pattern with high intake of ultra-processed fruits and vegetables (high ultra-processed), and one pattern with generally moderate intake of processed fruits and vegetables in all phytonutrient categories (moderate processed). There were subtle differences noted between NHANES III and Continuous NHANES cycles in those patterns with unprocessed fruits and vegetables and ultra-processed fruits and vegetables, with unprocessed fruits and vegetables and ultra-processed fruits and vegetables more common in some patterns.
In all cohorts and among participants with CKD, the most prevalent pattern was the overall low intake pattern. In adjusted analyses, the pattern was less common in those with CKD. Following adjustment for demographic and selected clinical variables (age, sex, race, waist circumference, diabetes, and hypertension), those with CKD were more likely to be classified as overall low intake in each cohort, compared with those without CKD.
The overall association of CKD with fruit and vegetable patterns was significant in NHANES III (P=.05) and Continuous NHANES 2003-2010 (P=.005). The difference was not significant in the Continuous NHANES 2011-2018 (P=.4).
The authors cited some limitations to the study findings, including the relatively modest classification diagnostics observed; the use of expert consensus and available literature to decide which fruits and vegetables are rich in carotenoids, polyphenols, or glucosinolates; and the inability to classify fruits and vegetables that may have been consumed in mixed dishes that could lead to some misclassification.
In conclusion, the researchers said, “To our knowledge, this study is novel in its interest in patterns of fruit and vegetable intake in the US population and in patients with CKD, with a focus on their phytochemical content and processing. Most of the current research on dietary intake in CKD has focused on single nutrients (eg, sodium, potassium, phosphorus, and protein) or simple foods. Dietary pattern is a complex phenotype. It is important to consider the interaction of nutrients in foods rather than isolating nutrients or restricting them in the diet. Understanding patterns of fruit and vegetable intake among CKD patients may provide a perspective different than traditional restrictive dietary guidelines.”
Takeaway Points
- Researchers reported results of a study designed to characterize patterns of fruit and vegetable intake in a cohort of US adults with and without chronic kidney disease (CKD).
- Four similar patterns were identified: overall low intake, high unprocessed, high ultra-processed, and moderate processed fruits and vegetables.
- In adjusted analyses, patients with CKD compared with those without CKD were more likely to be classified as overall low intake in each cohort.
