In this study, we compared the dietary behaviors and nutrient intake of prevalent HD and PD patients and found that PD patients had worse dietary behaviors and lower dietary intake compared to HD patients. In addition, the ratio of moderately to severely malnourished patients was slightly higher in the PD group than the HD group. Serum albumin and potassium levels were significantly lower in the PD group than the HD group.
The proportion of patients whose nutritional status deteriorated from well-nourished to malnourished or remained as malnourished for 1 year after the start of dialysis treatment was higher in the PD group than the HD group [11]. The changes in nutritional status assessed by SGA during the first year were associated with mortality in incident ESRD patients. In this study, PD patients had poorer dietary behaviors and subsequently less sufficient dietary intake compared to HD patients. It is associated with widespread malnutrition among PD patients, and it may be responsible for the overall higher mortality in PD patients than HD patients [18].
To investigate the nutritional status of participants, we evaluated SGA, BMI, MAC, and HGS [19]. SGA is a well-established tool to assess nutritional status and a feasible method to ascertain PEW [20-21]. There were four (13.3%) moderately to severely malnourished PD patients, while none of the HD patients was moderately to severely malnourished. BMI was higher in PD patients compared to HD patients, and MAC was not different between the two groups. In particular, HGS was significantly higher in PD patients than in HD patients, and we surmised that it was associated with the lower age of PD patients.
A recent study revealed that the nutritional status of HD and PD groups differs according to the dialysis vintage [22]. The dialysis duration < 2 years is associated with better hydration, nutritional state, and survival in PD patients, but longer dialysis duration reduces the benefits of the PD group. Dialysis vintage > 4 years is associated with similar hydration and mortality in both PD and HD groups. In this study, the mean duration of dialysis was 4–5 years in both groups. Therefore, considering the dialysis vintage of the patients included in this study, the higher proportion of malnourished patients in the PD group could have been expected.
Next, we compared the dietary behaviors of the HD and PD groups. In the dietary behavior survey, HD patients scored higher than PD patients on most of the questions, which means that the HD group had better dietary behaviors than the PD group. Although HD patients tend to skip their meal on the day of HD, we need to pay attention to the lower rate of eating three meals a day in PD patients. Poor appetite, which is frequently seen in PD patients [23], may be one of the reasons for this. In addition, PD patients’ intake of sugary or fried foods, which are usually recommended for sufficient energy intake in dialysis patients, was less than that of HD patients.
In the analysis of dietary intake using the Semi-FFQ, the HD group exhibited significantly higher consumption of dietary carbohydrates, dietary fat, dietary protein, and micronutrients than the PD group. A comparison of nutrient intake-to-recommended allowance ratio between the HD and PD groups [24-27] revealed that the HD group showed higher nutrient intake than the PD group.
The energy intake-to recommended allowance ratio in both HD and PD patients was low, and it was more prominent in the PD group than the HD group. However, considering energy intake from dialysate glucose [28], it is likely that the total energy intake of the PD group was similar to that of the HD group. A previous study comparing the nutritional status of HD and PD groups in Korea suggested that the HD group became malnourished due to a lack of energy intake and the PD group developed malnutrition due to a lack of protein intake [29]. In other words, intraperitoneal glucose absorption in dialysis fluid provides energy supplementation, but loss of protein through peritoneal fluid is more crucial for the development of malnutrition in PD patients. Based on the intake-to-recommended allowance ratio for dialysis patients, the rate of protein intake was 76.6% for the HD group and 81.7% for the PD group without statistically significant differences, which means that both HD and PD groups took less than the recommended amount in this study.
PEW is associated with mortality in patients with ESRD on maintenance HD [30], and this study also confirmed poor energy consumption by both HD and PD patients. In non-dialysis CKD patients, a neutral or slightly positive nitrogen balance can be maintained with a low-protein (0.6–0.8 g/kg/day) diet and restricted intake of sodium, potassium, and phosphorus [31-32]. In patients on maintenance HD and PD, however, their protein requirement is as high as 1.2–1.3 g/kg/day [26] for the compensation of dialysis-related protein loss, extra energy expenditure, and persistent inflammation [33]. In this study, neither HD nor PD patients consumed adequate amounts of energy and protein compared to the recommended allowance. It should receive attention to ensure better outcomes and maintain high quality of life.
We also analyzed the laboratory parameters to assess nutrient status indirectly. Serum albumin levels were significantly higher in the HD group than the PD group, which is consistent with the results of previous studies [34]. The serum albumin value is considered a biomarker of visceral protein and a fundamental parameter of nutritional assessment [35]. We suggest that one of the reasons for the low serum albumin levels in the PD group is the significantly lower protein intake, which was revealed from the Semi-FFQ, and protein loss via PD fluid. Recent studies show that a low serum albumin level rather reflects a state of persistent inflammation and has limited value as a marker of nutritional status only [36]. Therefore, efforts to not only increase dietary protein intake but also reduce systemic inflammation are needed to increase serum albumin levels in PD patients.
In this study, serum potassium levels were significantly lower in the PD group than the HD group. The intake of dietary potassium in the HD group was slightly over the recommended allowance, but that in the PD group was less than 80% of the recommended intake. Therefore, the lower level of serum potassium in PD patients may be attributed to their low potassium intake reported in the Semi-FFQ. A recent study suggested that low serum potassium is an independent risk factor for mortality in dialysis patients, and the major cause of death in PD patients with lower potassium was cardiovascular death and infection [37].
This study has several limitations. First, we did not use a diet diary for a complete nutrient assay. Although the Semi-FFQ, which was used in this study, was validated elsewhere [38], a dietary record complements the Semi-FFQ and ensures the completeness of the nutrient survey. Second, we did not evaluate the nitrogen balance or precise inflammatory status of subjects. Third, this was a cross-sectional study, and the participants were not followed. Therefore, the clinical effects of dietary behaviors and nutrient intake could not be investigated due to the cross-sectional study design. Finally, a small number of patients were included in this study. Therefore, the statistical power was low.