Pilot Randomized Controlled Trial of a Standard Versus a Modified Low-Phosphorus Diet in Hemodialysis Patients

Effect of a plant protein-rich diet on postprandial phosphate metabolism in healthy adult men: a randomised controlled trial

BACKGROUND

This study examined the effects of animal protein- and plant protein-rich diets on postprandial phosphorus metabolism in healthy male subjects.

METHODS

The study was conducted by randomised parallel-group comparison of healthy men aged 21-24 years. In Study 1, participants were divided into two groups and consumed either a 70% animal protein diet (AD, n = 6) or a 70% plant protein diet (PD, n = 6). In Study 2, participants were divided into three groups and consumed either AD (n = 10), PD (n = 10) or AD + DF, a 70% animal protein diet loaded with the same amount of fibre as PD (n = 9). The phosphorus contents of the diets used in this study were nearly equivalent (AD, 710.1 mg; PD, 709.7 mg; AD + DF, 708.9 mg). Blood and urine samples were collected before, and 2 and 4 h after the meal to measure phosphorus and calcium levels.

RESULTS

In Study 1, PD consumption resulted in lower blood and urinary phosphorus concentrations 2 h postprandially compared with AD (p < 0.05). In Study 2, blood phosphorus levels in AD + DF after the diet remained lower, but not significantly so compared with AD, and urinary phosphorus levels were significantly lower 2 h postprandially (p < 0.05).

CONCLUSIONS

A plant protein-rich diet reduced rapid postprandial increases in blood and urinary phosphorus concentrations compared with the animal protein-rich diets, suggesting that dietary fibre may play a partial role in the postprandial decreases in blood and urinary phosphorus concentrations.

Dietary Phosphate Educational Materials for Pediatric Chronic Kidney Disease: Are Confused Messages Reducing Their Impact?

OBJECTIVE

This study aimed to review the quality and content of phosphate educational materials used in pediatric chronic kidney disease.

METHODS

The quality of text-based (TB) pediatric phosphate educational materials was assessed using validated instruments for health literacy demands (Suitability Assessment of Materials, Patient Education Material Assessment Tool [PEMAT-P]) readability (Flesch Reading Ease, and Flesch-Kincaid Grade Level). Codes were inductively derived to analyse format, appearance, target audience, resource type, and content, aiming for intercoder reliability > 80%. The content was compared to Pediatric Renal Nutrition Taskforce (PRNT) recommendations.

RESULTS

Sixty-five phosphate educational materials were obtained; 37 were pediatric-focused, including 28 TB. Thirty-two percent of TB materials were directed at caregivers, 25% at children, and 43% were unspecified. Most (75%) included a production date, with 75% produced >2 years ago. The median Flesch Reading Easetest score was 68.2 (interquartile range [IQR] 61.1-75.3) and Flesch-Kincaid Grade Level was 5.6 (IQR 4.5-7.7). Using Suitability Assessment of Materials, 54% rated "superior" (≥70), 38% rated "adequate" (40-69), and 8% rated "not suitable" (≤39). Low-scoring materials lacked a summary (12%), cover graphics (35%), or included irrelevant illustrations (50%). Patient Education Material Assessment Tool-P scores were 70% (IQR 50-82) for understandability and 50% (IQR 33-67) for actionability. An intercoder reliability of 87% was achieved. Over half of limited foods are in agreement with PRNT (including 89% suggesting avoiding phosphate additives). Recommendations conflicting with PRNT included reducing legumes and whole grains. Over a third contained inaccuracies, and over two-thirds included no practical advice.

CONCLUSIONS

TB pediatric phosphate educational materials are pitched at an appropriate level for caregivers, but this may be too high for children under 10 years. The inclusion of relevant illustrations may improve this. Three-quarters of materials scored low for actionability. The advice does not always align with the PRNT, which (together with the inaccuracies reported) could result in conflicting messages to patients and their families.

Plant-based diets and postprandial hyperkalemia

This Letter to the Editor is a response to St-Jules and Fouque and their interpretation of postprandial hyperkalemia, especially regarding plant-based diets. Based on the reviewed literature review, potassium kinetic studies cited by the authors include only 1 study with a food-based intervention that actually showed reduced postprandial hyperkalemia with plant-based diets. The remainder of the studies used potassium salts or supplements that behave differently compared with whole plant foods. As such, we recommend avoiding restriction of whole plant foods in patients with chronic kidney disease when solely based on the theoretical risk of postprandial hyperkalemia.

Food to Prevent Vascular Calcification in Chronic Kidney Disease

Vascular calcification (VC) is a consequence of chronic kidney disease (CKD) which is of paramount importance regarding the survival of CKD patients. VC is far from being controlled with actual medication; as a result, in recent years, diet modulation has become more compelling. The concept of medical nutritional therapy points out the idea that food may prevent or treat diseases. The aim of this review was to evaluate the influence of food habits and nutritional intervention in the occurrence and progression of VC in CKD. Evidence reports the harmfulness of ultra-processed food, food additives, and animal-based proteins due to the increased intake of high absorbable phosphorus, the scarcity of fibers, and the increased production of uremic toxins. Available data are more supportive of a plant-dominant diet, especially for the impact on gut microbiota composition, which varies significantly depending on VC presence. Magnesium has been shown to prevent VC but only in experimental and small clinical studies. Vitamin K has drawn considerable attention due to its activation of VC inhibitors. There are positive studies; unfortunately, recent trials failed to prove its efficacy in preventing VC. Future research is needed and should aim to transform food into a medical intervention to eliminate VC danger in CKD.

Still no direct evidence of postprandial hyperkalemia with plant foods

Although St-Jules et al have presented the case for postprandial hyperkalemia with food, including plant foods, there (still) is little to no direct evidence supporting the occurrence of postprandial hyperkalemia, mostly due to a lack of studies performed exclusively using food. Food is different than salts or supplements, and it is likely that a banana behaves differently than potassium salts. A growing body of evidence supports the use of plant foods without causing hyperkalemia in patients with kidney disease. Currently, only 1 study has reported on the postprandial effects of hyperkalemia. In this study, there was a substantial reduction in the instances of postprandial hyperkalemia in participants consuming a diet that included more plant foods and more fiber. At the time of this writing, there is no evidence to support risk or safety of certain foods with regard to postprandial hyperkalemia, and additional research is warranted.

Recommendations of the Spanish Society of Nephrology for the management of mineral and bone metabolism disorders in patients with chronic kidney disease: 2021 (SEN-MM)

As in 2011, when the Spanish Society of Nephrology (SEN) published the Spanish adaptation to the Kidney Disease: Improving Global Outcomes (KDIGO) universal Guideline on Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD), this document contains an update and an adaptation of the 2017 KDIGO guidelines to our setting. In this field, as in many other areas of nephrology, it has been impossible to irrefutably answer many questions, which remain pending. However, there is no doubt that the close relationship between the CKD-MBD/cardiovascular disease/morbidity and mortality complex and new randomised clinical trials in some areas and the development of new drugs have yielded significant advances in this field and created the need for this update. We would therefore highlight the slight divergences that we propose in the ideal objectives for biochemical abnormalities in the CKD-MBD complex compared to the KDIGO suggestions (for example, in relation to parathyroid hormone or phosphate), the role of native vitamin D and analogues in the control of secondary hyperparathyroidism and the contribution of new phosphate binders and calcimimetics. Attention should also be drawn to the adoption of important new developments in the diagnosis of bone abnormalities in patients with kidney disease and to the need to be more proactive in treating them. In any event, the current speed at which innovations are taking place, while perhaps slower than we might like, globally drives the need for more frequent updates (for example, through Nefrología al día).

Currently Available Handouts for Low Phosphorus Diets in Chronic Kidney Disease Continue to Restrict Plant Proteins and Minimally Processed Dairy Products

OBJECTIVES

The 2020 Kidney Disease Outcome Quality Initiative guidelines recommend adjusting phosphorus intake to achieve and maintain normal serum phosphorus levels for adults living with chronic kidney disease. These guidelines also recommend considering the dietary source of phosphorus as different sources have different bioavailability; however, phosphorus food lists are not provided. Therefore, the aim of this study is to investigate the current teaching materials in Canada regarding low phosphorus diet.

DESIGN AND METHODS

Using a geographical approach, websites from each province and territories' government, health, and renal programs (where applicable) were reviewed for resources on dietary phosphorus restriction in chronic kidney disease. All publicly available handouts/booklets/printable webpages were obtained and reviewed for recommendations on how to implement a low phosphorus diet.

RESULTS

Sixty-one resources in total met inclusion criteria (52 handouts from health agencies in 6 provinces and 9 handouts from the Kidney Foundation of Canada). Items with minimal nutrition value, such as cola, beer and cocoa, chocolate, and baking powder, were the most commonly restricted with 84% (51/61) resources making this recommendation. Plant proteins and minimally processed dairy were restricted in 80% (49/61) of resources. Processed animal meat was recommended to be restricted in 70% (43/61) of resources and whole grains in 65% (40/61). Sixty-three percent of the handouts (39/61) discuss avoiding phosphorus additives.

CONCLUSIONS

Many resources restrict items with minimal nutrition value to lower phosphorus intake; however, plant foods, including plant proteins and whole grains, continue to be restricted in the majority of resources, despite having lower bioavailability. The 2020 Kidney Disease Outcome Quality Initiative guidelines recommend considering bioavailability of phosphorus source when implementing low phosphorus diets; current handouts in Canada would likely benefit from review.

The “FIFTY SHADOWS” of the RALES Trial: Lessons about the Potential Risk of Dietary Potassium Supplementation in Patients with Chronic Kidney Disease

Hyperkalaemia (HK) is one of the most common electrolyte disorders and a frequent reason for nephrological consultations. High serum potassium (K⁺) levels are associated with elevated morbidity and mortality, mainly due to life-threatening arrhythmias. In the majority of cases, HK is associated with chronic kidney disease (CKD), or with the use of renin–angiotensin–aldosterone system inhibitors (RAASis) and/or mineral corticoid antagonists (MRAs). These drugs represent the mainstays of treatment in CKD, HF, diabetes, hypertension, and even glomerular diseases, in consideration of their beneficial effect on hard outcomes related to cardiovascular events and CKD progression. However, experiences in relation to the Randomised Aldactone Evaluation Study (RALES) cast a long shadow that extends to the present day, since the increased risk for HK remains a major concern. In this article, we summarise the physiology of K⁺ homeostasis, and we review the effects of dietary K⁺ on blood pressure and cardiovascular risk in the general population and in patients with early CKD, who are often not aware of this disease. We conclude with a note of caution regarding the recent publication of the SSaSS trial and the use of salt substitutes, particularly in patients with a limited capacity to increase K⁺ secretion in response to an exogenous load, particularly in the context of “occult” CKD, HF, and in patients taking RAASis and/or MRAs.

The effect of egg white diet on phosphorus control in dialysis patients

INTRODUCTION

Nutritional interventions have been envisaged to improve hyperphosphatemia and malnutrition, two important risk factors associated with mortality in dialysis patients. We evaluated the effects of egg white consumption on serum phosphate and malnutrition in dialysis patients.

METHODS

In an open-label, per protocol clinical trial, conducted in Kerman dialysis centers, 150 hemodialysis patients aged ≥18 years with serum phosphorus ≥5.5 mg/dl were included in the study. All participants limited their intake of foods containing phosphorus for 4 weeks, and then they were divided into a control and an intervention group. The control group continued their ordinary diet and the participants in the intervention group consumed a Telavang egg white pack (containing six egg whites, 96 calories, 24 g protein) as a substitute for meat products 3 days a week for 8 weeks. Finally, changes in serum albumin, phosphorus, calcium, PTH, and cholesterol were measured.

FINDINGS

At the baseline, there were no significant differences in the laboratory variables between the two groups. After 8 weeks, serum cholesterol (124.3 ± 38.1, vs. 135.8 ± 28.8, p = 0.003) and phosphorus levels (4.5 ± 1.03, vs. 6.7 ± 1.5, p = 0.001) were significantly lower in the intervention group compared with the control group. Also, serum albumin (4.5 ± 0.07 vs. 3.7 ± 0.4, p = 0.001) was significantly higher in the intervention group. Moreover, phosphorus, PTH, and cholesterol levels in the intervention group were significantly lower than their baseline values (p = 0.001).

CONCLUSION

The results showed that the egg white could be a useful source of protein for dialysis patients, as it simultaneously reduces serum phosphorus and cholesterol, and increases serum albumin.

Recent Advances in the Role of Diet in Bone and Mineral Disorders in Chronic Kidney Disease

PURPOSE OF REVIEW

Chronic kidney disease mineral and bone disease (CKD-MBD) is a common complication of kidney disease and is strongly influenced by diet. The purpose of this manuscript is to review recent advances in the role of diet in CKD-MBD over the last 5 years.

RECENT FINDINGS

Many of the recent studies examining the role of diet in CKD-MBD have focused on the adverse effects of high phosphorus consumption on bone health and metabolism. In general, the studies have shown that high phosphorus consumption worsens markers of bone and mineral metabolism but that eating a diet with a calcium to phosphorus ratio closer to 1:1 can attenuate some of these effects. Recent studies also showed that dietary counseling is efficacious for improving markers of CKD-MBD. High consumption of phosphorus aggravates CKD-MBD. Dietary counseling may ameliorate these effects, for example, by consuming diets with higher calcium to phosphorus ratios.

The Impact of Protein Type on Phosphorus Intake, Serum Phosphate Concentrations, and Nutrition Status in Adults with Chronic Kidney Disease: A Critical Review

Lower phosphorus intake to prevent hyperphosphatemia for those with chronic kidney disease (CKD) is often recommended. Plant proteins are frequently restricted for their high phosphorus content despite having lower bioavailability. To summarize the evidence on protein type and dietary phosphorus intake, serum phosphate concentrations, and nutritional adequacy in adults with CKD, a search in MEDLINE via Ovid was conducted. Citation lists were reviewed to identify any additional articles. Sixteen articles were included-7 intervention (n = 290) and 9 observational (n = 4933). All intervention trials reported high-plant-protein diets provided adequate protein and adhered to low phosphorus diet guidelines. All intervention trials reported higher plant-protein intake was associated with lower serum phosphate; however, only 2 achieved statistical significance. For observational studies, 2 reported that higher proportions of plant to animal protein resulted in lower phosphorus intake but equivalent serum phosphate concentrations. Two reported that plant protein and animal protein had equivalent correlation values to phosphorus intake and no correlation to serum phosphate concentrations. One trial reported lower total phosphorus and protein intake among those who consumed more plant proteins but did not examine serum concentrations. Four reported lower serum phosphate concentrations among those who consumed more plant proteins but did not report dietary phosphorus intake. Of the observational studies that reported on protein intake, all reported lower protein intake among those with higher versus lower plant-protein intake. BMI tended to be lower among those consuming more plant protein. There was not a consistent relation between protein type and albumin concentrations. Routine restriction of plant-protein foods to prevent hyperphosphatemia in CKD would likely benefit from re-evaluation, as evidence does not suggest that higher plant-protein intake leads to higher serum phosphate concentrations or worse nutritional status, although longer-duration intervention trials with larger sample sizes appear to be warranted.

The effect of dietary phosphorus load and food matrix on postprandial serum phosphate in hemodialysis patients: a pilot study

Background: Potential dietary strategies for controlling hyperphosphataemia include the use of protein sources with lower phosphorus bioavailability such as pulses and nuts, focus on phosphorus to protein ratios and the avoidance of all phosphate additives. Methods: We conducted a controlled crossover feeding study in 8 haemodialysis (HD) patients to investigate the acute postprandial effect of a modified versus standard low phosphorus diet for one day on serum phosphate, potassium and intact parathyroid levels in prevalent HD patients. Each participant consumed the modified diet on one day and the standard diet on a second day one week apart. The modified diet included beef and less dairy, with a lower phosphorus to protein ratio, as well as plant-based protein, whole grains, pulses and nuts containing phytates which reduces phosphorus bioavailability. Both diets were tailored for each participant to provide 1.1g protein/kg ideal body weight. Participants provided fasting bloods before breakfast, a pre-prandial sample before the lunch time main meal and samples at one-hour intervals for the four hours after the lunch time main meal, for analysis of phosphate, potassium and intact parathyroid hormone (iPTH). Results: At four hours post the lunch time main meal on each study day, individuals on the modified diet had serum phosphate readings 0.30 mmol/l lower than when on the standard diet (p-value = 0.015, 95% confidence interval [CI] -0.57, -0.04). The corresponding change in serum potassium at four hours was a decrease of 0.675 mmol/l (p-value = 0.011, CI -1.25, -0.10). Conclusions: Decreases in both serum phosphate and serum potassium readings on a modified low phosphorus diet encourage further larger studies to explore the possibility of greater food choice and healthier plant-based diets in HD patients.  ClinicalTrials.gov registration: NCT04845724 (15/04/2021)