Controlled comparison of 20-g and 40-g protein diets in the treatment of chronic uremia

The Role of Plant-Based Diets in Preventing and Mitigating Chronic Kidney Disease: More Light than Shadows

Chronic kidney disease (CKD) is a non-communicable disease that affects >10% of the general population worldwide; the number of patients affected by CKD is increasing due in part to the rise in risk factors such as obesity, hypertension, and diabetes mellitus. As many studies show, diet can be an important tool for preventing and mitigating the onset of non-communicable diseases. Plant-based diets (PBDs) are those that emphasize the consumption of plant foods and may or may not include small or moderate amounts of animal foods. Recently, these diets have received increasing interest because they have been associated with favourable effects on health and also appear to protect against the development and progression of CKD. PBDs, which are associated with protein restrictions, seem to offer adjunctive advantages in patients with chronic kidney disease, as compared to conventional low-protein diets that include animal proteins. The principal aims of this review are to provide a comprehensive overview of the existing literature regarding the role of plant-based diets and low-protein, plant-based diets in the context of chronic kidney disease. Moreover, we try to clarify the definition of plant-based diets, and then we analyse possible concerns about the use of PBDs in patients with chronic kidney disease (nutritional deficiency and hyperkalaemia risk). Finally, we offer some strategies to increase the nutritional value of plant-based low-protein diets. In the Materials and Methods section, many studies about plant-based diets and low-protein plant-based diets (e.g., the very-low-protein diet and vegan low-protein diet, LPD) in chronic kidney disease were considered. In the Results and Conclusion section, current data, most from observational studies, agree upon the protective effect of plant-based diets on kidney function. Moreover, in patients with advanced CKD, low-protein plant-based options, especially a very-low-protein diet supplemented with heteroanalogues (VLPDs), compared to a conventional LPD appear to offer adjunctive advances in terms of delaying dialysis and mitigating metabolic disturbances. However, further studies are necessary to better investigate the possible metabolic and cardiovascular advantages of plant-based LPDs versus conventional LPDs.

Low protein diets for non-diabetic adults with chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is defined as reduced function of the kidneys present for 3 months or longer with adverse implications for health and survival. For several decades low protein diets have been proposed for participants with CKD with the aim of slowing the progression to end-stage kidney disease (ESKD) and delaying the onset of renal replacement therapy. However the relative benefits and harms of dietary protein restriction for preventing progression of CKD have not been resolved. This is an update of a systematic review first published in 2000 and updated in 2006, 2009 and 2018.

OBJECTIVES

To determine the efficacy of low protein diets in preventing the natural progression of CKD towards ESKD and in delaying the need for commencing dialysis treatment in non-diabetic adults.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to 7 September 2020 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) or quasi RCTs in which adults with non-diabetic CKD (stages 3 to 5) not on dialysis were randomised to receive a very low protein intake (0.3 to 0.4 g/kg/day) compared with a low protein intake (0.5 to 0.6 g/kg/day) or a low protein intake compared with a normal protein intake (≥ 0.8 g/kg/day) for 12 months or more.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies and extracted data. For dichotomous outcomes (death, all causes), requirement for dialysis, adverse effects) the risk ratios (RR) with 95% confidence intervals (CI) were calculated and summary statistics estimated using the random effects model. Where continuous scales of measurement were used (glomerular filtration rate (GFR), weight), these data were analysed as the mean difference (MD) or standardised mean difference (SMD) if different scales had been used. The certainty of the evidence was assessed using GRADE.

MAIN RESULTS

We identified 17 studies with 2996 analysed participants (range 19 to 840). Four larger multicentre studies were subdivided according to interventions so that the review included 21 separate data sets. Mean duration of participant follow-up ranged from 12 to 50 months. Random sequence generation and allocation concealment were considered at low risk of bias in eleven and nine studies respectively. All studies were considered at high risk for performance bias as they were open-label studies. We assessed detection bias for outcome assessment for GFR and ESKD separately. As GFR measurement was a laboratory outcome all studies were assessed at low risk of detection bias. For ESKD, nine studies were at low risk of detection bias as the need to commence dialysis was determined by personnel independent of the study investigators. Five studies were assessed at high risk of attrition bias with eleven studies at low risk. Ten studies were at high risk for reporting bias as they did not include data which could be included in a meta-analysis. Eight studies reported funding from government bodies while the remainder did not report on funding. Ten studies compared a low protein diet with a normal protein diet in participants with CKD categories 3a and b (9 studies) or 4 (one study). There was probably little or no difference in the numbers of participants who died (5 studies 1680 participants: RR 0.77, 95% CI 0.51 to 1.18; 13 fewer deaths per 1000; moderate certainty evidence). A low protein diet may make little or no difference in the number of participants who reached ESKD compared with a normal protein diet (6 studies, 1814 participants: RR 1.05, 95% CI 0.73 to 1.53; 7 more per 1000 reached ESKD; low certainty evidence). It remains uncertain whether a low protein diet compared with a normal protein intake impacts on the outcome of final or change in GFR (8 studies, 1680 participants: SMD -0.18, 95% CI -0.75 to 0.38; very low certainty evidence). Eight studies compared a very low protein diet with a low protein diet and two studies compared a very low protein diet with a normal protein diet. A very low protein intake compared with a low protein intake probably made little or no difference to death (6 studies, 681 participants: RR 1.26, 95% CI 0.62 to 2.54; 10 more deaths per 1000; moderate certainty evidence). However it probably reduces the number who reach ESKD (10 studies, 1010 participants: RR 0.65, 95% CI 0.49 to 0.85; 165 per 1000 fewer reached ESKD; moderate certainty evidence). It remains uncertain whether a very low protein diet compared with a low or normal protein intake influences the final or change in GFR (6 studies, 456 participants: SMD 0.12, 95% CI -0.27 to 0.52; very low certainty evidence). Final body weight was reported in only three studies. It is uncertain whether the intervention alters final body weight (3 studies, 89 participants: MD -0.40 kg, 95% CI -6.33 to 5.52; very low certainty evidence).Twelve studies reported no evidence of protein energy wasting (malnutrition) in their study participants while three studies reported small numbers of participants in each group with protein energy wasting. Most studies reported that adherence to diet was satisfactory. Quality of life was not formally assessed in any studies.

AUTHORS' CONCLUSIONS

This review found that very low protein diets probably reduce the number of people with CKD 4 or 5, who progress to ESKD. In contrast low protein diets may make little difference to the number of people who progress to ESKD. Low or very low protein diets probably do not influence death. However there are limited data on adverse effects such as weight differences and protein energy wasting. There are no data on whether quality of life is impacted by difficulties in adhering to protein restriction. Studies evaluating the adverse effects and the impact on quality of life of dietary protein restriction are required before these dietary approaches can be recommended for widespread use.

Pro: The rationale for dietary therapy for patients with advanced chronic kidney disease

Dietary treatment offers many benefits to patients with advanced chronic kidney disease (CKD) who are approaching the need for renal replacement therapy. A large number of these benefits are independent of whether diets slow the rate of progression of CKD. These diets are low in protein and many minerals, and provide adequate energy for the CKD patient. The diets can reduce accumulation of potentially toxic metabolic products derived from protein and amino acid degradation, maintain a healthier balance of body water, sodium, potassium, phosphorus, calcium and other minerals, and prevent or improve protein-energy wasting. Such diets may enable patients to safely delay the onset of chronic dialysis therapy or kidney transplantation. Dietary therapy may also augment the effectiveness of infrequent or incremental dialysis by maintaining healthier metabolic and clinical status and may enable some end-stage renal disease patients to avoid the need for temporary placement of hemodialysis catheters while their arterial venous fistulae or grafts mature. The anxiety that many advanced CKD patients commonly experience with regard to starting dialysis may incentivize them to accept and adhere to dietary therapy.

Current Uses of Dietary Therapy for Patients with Far-Advanced CKD

For several decades, inquiry concerning dietary therapy for nondialyzed patients with CKD has focused mainly on its capability to retard progression of CKD. However, several studies published in recent years indicate that, independent of whether diet can delay progression of CKD, well designed low-protein diets may provide a number of benefits for people with advanced CKD who are close to requiring or actually in need of RRT. Dietary therapy may both maintain good nutritional status and safely delay the need for chronic dialysis in such patients, offering the possibility of improving quality of life and reducing health care costs. With the growing interest in incremental dialysis, dietary therapy may enable lower doses of dialysis to be safely and effectively used, even as GFR continues to decrease. Such combinations of dietary and incremental dialysis therapy might slow the rate of loss of residual GFR, possibly reduce mortality in patients with advanced CKD, improve quality of life, and also, reduce health care costs. The amount of evidence that supports these possibilities is limited, and more well designed, randomized clinical trials are clearly indicated.

The mean dietary protein intake at different stages of chronic kidney disease is higher than current guidelines

The actual dietary protein intake of adults without and with different stages of chronic kidney disease is not known. To evaluate this we performed cross-sectional analyses of 16,872 adults (20 years of age and older) participating in the National Health and Nutrition Examination Survey 2001-2008 who completed a dietary interview by stage of kidney disease. Dietary protein intake was assessed from 24-h recall systematically collected using the Automated Multiple Pass Method. Complex survey analyses were used to derive population estimates of dietary protein intake at each stage of chronic kidney disease. Using dietary protein intake of adults without chronic kidney disease as the comparator, and after adjusting for age, the mean dietary protein intake was 1.30 g/kg ideal body weight/day (g/kgIBW/d) and was not different from stage 1 or stage 2 (1.28 and 1.25 g/kgIBW/d, respectively), but was significantly different in stage 3 and stage 4 (1.22 and 1.13 g/kgIBW/d, respectively). These mean values appear to be above the Institute of Medicine requirements for healthy adults and the NKF-KDOQI guidelines for stages 3 and 4 chronic kidney disease. Thus, the mean dietary protein intake is higher than current guidelines, even after adjusting for age.

Dietary protein restriction benefits patients with chronic kidney disease (Review Article)

The prevalence of chronic kidney disease (CKD) is rapidly increasing so every strategy should be used to avoid the complications of CKD. Most CKD symptoms or uraemia are caused by protein intolerance; symptoms arise because the patient is unable to excrete metabolic products of dietary protein and the ions contained in protein-rich foods. Consequently, CKD patients accumulate salt, phosphates, uric acid and many nitrogen-containing metabolic products, and secondary problems of metabolic acidosis, bone disease and insulin resistance become prominent. These problems can be avoided with dietary planning. Protein-restricted diets do not produce malnutrition and with these diets even patients with advanced CKD maintain body weight, serum albumin and normal electrolyte values. Non-compliance is a problem, but this can be detected using standard techniques to provide the patient with appropriate responses. The role of dietary protein restriction in the progression of CKD has not been proven, but it can reduce albuminuria and will prevent uraemic symptoms. Until a means of preventing kidney disease or progression is found, safe methods of management such as dietary manipulation should be available for CKD patients.

Effect of nonsupplemented low-protein diet on very late stage CRF

BACKGROUND

There are few reports of the effect of a low-protein diet on very late-stage chronic renal failure (CRF), eg, serum creatinine level greater than 10 mg/dL (884 micromol/L). In this retrospective study, we examined the effects of a very low-protein diet in patients with very late-stage CRF.

METHODS

A very low-protein diet (0.25 to 0.54 g/kg body weight/d [0.39 +/- 0.01g/kg body weight/d]) without supplementation of essential amino acids or keto analogues was administered to 76 patients with very late-stage CRF who had serum creatinine levels greater than 10 mg/dL (884 micromol/L). Twenty-one patients with the same serum creatinine level and protein intake of 0.55 to 1.2 g/kg body weight/d (0.68 +/- 0.03 g/kg body weight/d) were observed in lieu of controls.

RESULTS

Blood urea nitrogen was significantly suppressed to 43.1 +/- 1.9 g/dL (15.4 +/- 0.7 mmol/L) in the low-protein group compared with 111.2 +/- 7.0 mg/dL (39.7 +/- 2.5 mmol/L; P < 0.001) in the control group. The rate of decline in glomerular filtration rate (creatinine clearance) was 36-fold slower with the low-protein diet (-7.1 +/- 1.0 versus -0.2 +/- 0.4 mL/mon, respectively; P < 0.001). Nutritional state in the low-protein group exceeded that of the control group. Consequently, the renal survival rate improved significantly (P < 0.0001). All patients in the control group were initiated on dialysis treatment within 6 months from a serum creatinine level of 10 mg/dL (884 micromol/L). Conversely, 58% of the low-protein group are still on predialysis treatment.

CONCLUSION

A severe low-protein diet is effective not only in preventing deterioration in renal function, but also in maintaining nutritional state despite no supplementation of essential amino acids or keto analogues, even as serum creatinine level is more than 10 mg/dL (884 micromol/L).

History of the professional councils of the National Kidney Foundation

As the Councils move toward the new millennium, efforts to improve outcomes for patients with renal disease will be at the forefront. Each council has established a commitment to improving the quality of life for these individuals. Toward this goal, the CNNT, the CRN, and the CNSW will each propose programs to the NKF for improving the knowledge and skills of the professionals within these councils, promoting research within the respective scope of these professions, and working together to bring a better understanding of the issues confronted by the patients and the professionals as well. As an example of the combined effort of the Councils, the first joint project of the century will be to bring the communications packages of each council under a common framework by joining the newsletters of each council. It is an exciting time to be part of the NKF. As a professional in the renal community, being a part of the CNNT, the CRN, or the CNSW offers a professional enrichment and opportunities to participate in making lives better for those with renal disease.

Nutrition and the kidney: how to manage patients with renal failure

Nutrition is believed to play a key role in the management of chronic and acute renal failure. Considerable evidence suggests that unrestricted protein diets accelerate the progression of chronic renal failure. As a result, recommendations have evolved limiting the quantity and quality of nitrogen intake with the goal of slowing the progression to dialysis dependency. Acute renal failure offers different challenges in view of its common association with hypermetabolic states. With respect to nitrogen substrate administration, the use of mixed formulations of essential plus nonessential amino acids seems to be as effective as essential amino acids alone.

Free and protein-bound tryptophan in serum of untreated patients with chronic renal failure

In fasting sera from 46 untreated patients with chronic renal failure and in 22 normal subjects, non-protein-bound tryptophan, F, was separated by pH-controlled equilibrium dialysis. Total tryptophan, T, and F were measured by HPLC. Results in patients were related to gender, severity of chronic renal failure (as measured by radioisotopic glomerular filtration rate), protein intake (as measured by 24-hr urinary urea N excretion), and protein nutrition (as measured by serum concentrations of albumin and transferrin). T was subnormal in 59% of the patients. In seven hypoalbuminemic patients, F/T was markedly increased (approaching unity) but F was normal. In 39 non-hypoalbuminemic patients, F was again normal but F/T was often increased at glomerular filtration rates below 30 ml/min/3 m2 of height2, especially in females. T was significantly correlated with estimated protein intake (r = 0.54, P = 0.0004), even though neither F nor serum protein levels were correlated with it. We conclude that the serum level of free tryptophan is well-maintained in chronic renal failure, being uninfluenced by severity of renal insufficiency, voluntary protein intake, or serum protein concentrations. On the other hand, protein-bound tryptophan varies with protein intake, decreases markedly in hypoalbuminemic patients, and also decreases in many nonhypoalbuminemic patients (especially females) when the glomerular filtration rate falls below approximately 30 ml/min/3 m2 of height2.

Effects of dietary protein and phosphorus restriction on the progression of chronic renal failure

In recent years, evidence has accumulated suggesting that early dietary intervention in the form of protein restriction can dramatically alter the natural history of chronic renal insufficiency. This article reviews the literature in this area and summarizes the questions that remain for future investigators to answer. Interest in the role of protein intake in renal disease dates back to the early 1900s, when several investigators found that the progression of renal failure was accelerated in rats and rabbits fed high-protein diets. Subsequent work in animal models has demonstrated that nephron loss, resulting from a variety of disease states, is associated with elevated intraglomerular pressures and flows. Several investigators now have postulated that these abnormal hemodynamics, resulting from intrarenal vasodilation and hyperperfusion, damage the glomerulus and may produce further nephron loss independent of the initial renal insult. Dietary protein restriction appears to reduce these pressures and flows towards normal in animals, although the operative mechanism has yet to be identified. Limited studies of dietary protein restriction in human renal disease have suggested a beneficial effect, but carefully controlled prospective studies will be necessary to establish clear therapeutic efficacy.