Long-term protein intake control in kidney transplant recipients: effect in kidney graft function and in nutritional status

A holistic review of sodium intake in kidney transplant patients: More questions than answers

Kidney transplantation (KT) is the best treatment option for end-stage kidney disease (ESKD). Acute rejection rates have decreased drastically in recent years but chronic kidney allograft disease (CKAD) is still an important cause of allograft failure and return to dialysis. Thus, there is unmet need to identify and reverse the cause of CKAD. Additionally, cardiovascular events after KT are still leading causes of morbidity and mortality. One overlooked potential contributor to CKAD and adverse cardiovascular events is increased sodium/salt intake in kidney transplant recipients (KTRs). In general population, the adverse effects of high sodium intake are well known but in KTRs, there is a paucity of evidence despite decades of experience with KT. Limited research showed that sodium intake is high in most KTRs. Moreover, excess sodium intake is associated with elevated blood pressure and albuminuria in some studies involving KTRs. There is also experimental evidence suggesting that increased sodium intake is associated with histologic graft damage. Critical knowledge gaps still remain, including the exact amount of sodium restriction needed in KTRs to optimize outcomes and allograft survival. Additionally, best methods to measure sodium intake and practices to follow-up are not clarified in KTRs. To meet these deficits, prospective long term studies are warranted in KTRs. Moreover, preventive measures must be determined and implemented both at individual and societal levels to achieve sodium restriction in KTRs.

Dietary protein intake and plant-dominant diets to mitigate risk of allograft dysfunction progression in kidney transplant recipients

PURPOSE OF REVIEW

There are limited studies on the benefits of low dietary protein intake (DPI) and plant-dominant diets to delay kidney allograft dysfunction. We evaluate evidence regarding the association or effects of the amount and type of DPI on allograft function.

RECENT FINDINGS

There is conflicting evidence regarding the benefits of low DPI and plant-dominant diet including PLADO and PLAFOND on kidney allograft function. Taking the strength of evidence including study design, sample size, and time to follow-up, the proposed amount of DPI to slow the progression of allograft dysfunction, avoid negative nitrogen balance, and skeletal muscle mass loss is 1.0-1.3 g/kg/day during an immediate posttransplant period or when high protein catabolic rate exists. The DPI may be 0.8-1.0 g/kg/day in patients with stable allograft function. Patients with chronic allograft rejection or estimated glomerular filtration rate <25 ml/min may benefit from the DPI of 0.55-0.60 g/kg/day, while those with failed allograft requiring transition to dialysis including incremental (twice-weekly) hemodialysis should consider increasing DPI to 1.0-1.2 g/kg/day.

SUMMARY

While there is a lack of strong evidence, individualized approaches based on the patient's comorbidities, net state of immunosuppression, and periods posttransplant may guide the appropriate amount and type of DPI to slow allograft dysfunction.

Changes in Dietary Nutrient Intake and Estimated Glomerular Filtration Rate over a 5-Year Period in Renal Transplant Recipients

The scarcity of dietary guidance for renal transplant recipients (RTRs) raises concerns regarding obesity and associated comorbidities, including impaired renal function. This two-stage cross-sectional study examined longitudinal changes in dietary nutrient intake in the same individuals over a 5-year interval. This study involved two stages: T1 (September 2016 to June 2018) and T2 (July 2022 to August 2023). The average duration between the two data collection stages was 6.17 ± 0.42 (range 5.20-6.87) years. The study included 227 RTRs with an average age and time since transplant of 49.97 ± 12.39 and 9.22 ± 7.91 years, respectively. Of the 35 patients who participated in both phases, fewer than half met the recommended intakes for energy, dietary fiber, and most vitamins and minerals, as set in the Dietary Reference Intakes (DRIs) or by the Dietitian Association Australia (DAA). Over half exceeded the DRI recommended intake for total protein, and more than 80% of the protein consumed per kilogram of body weight exceeded the DAA's recommendations. In the T2 stage, the RTRs had a significantly higher blood urea nitrogen level, lower albumin level, and estimated glomerular filtration rate. These findings indicate that deteriorating dietary intake in RTRs can adversely affect their nutritional status and transplanted kidney function over a 5-year period.

High Alternative Health Eating Index-Taiwan Scores Are Associated With Prevention of Graft Dysfunction in Taiwanese Renal Transplant Recipients

BACKGROUND

Various dietary quality indices demonstrate that a higher dietary quality score is associated with a reduced risk of several chronic diseases. However, creating an index tailored to the national population is crucial. The study investigated the association between the Alternative Healthy Eating Index-Taiwan (AHEI-Taiwan) and graft dysfunction in Taiwanese renal transplant recipients (RTRs).

METHODS

A prospective cohort study recruited 102 RTRs with a functioning allograft without acute rejection in the last 3 months from September 2016 to June 2018. Laboratory data were obtained from the medical records of patients. Graft dysfunction was indicated by an estimated glomerular filtration rate (eGFR) <60 mL/min per 1.73 m² in accordance with the Kidney Disease Outcomes Quality Initiative guideline. The dietary quality index AHEI-Taiwan was adapted from the AHEI based on Taiwanese dietary recommendations.

RESULTS

Mean age, renal transplant time, and eGFR were 48.9 ± 12.8 years, 8.5 ± 5.8 years, and 54.9 ± 17.8 mL/min per 1.73 m², respectively, in 102 RTRs. The RTRs with the highest quartile of AHEI-Taiwan scores were older and had a higher eGFR. Logistic regression analysis adjusted for age, sex, calories, Charlson comorbidity index, transplant time, and dialysis time showed that the highest quartile of the AHEI-Taiwan was associated with an 88% (odds ratio, 0.12; 95% CI, 0.03-0.59, P < .01) lower risk of graft dysfunction.

CONCLUSION

A high AHEI-Taiwan score was associated with a reduced risk of graft dysfunction in Taiwanese RTRs.

What is Known About Dietary Interventions and Body Weight Management After Kidney Transplantation? A Scoping Review

OBJECTIVE

Several studies report weight gain after kidney transplantation, which is commonly related to poor outcomes. However, recommendations for dietary interventions aiming to manage these patients' weight are still scarce in the literature. Thus, this review seeks to describe the state of literature on the effect of dietary interventions on weight after kidney transplantation.

DESIGN

Scoping review.

METHODS

This review was designed according to the recommendations for scoping reviews elaborated by the Joanna Briggs Institute. Studies assessing the effect of dietary interventions on body weight after kidney transplantations were searched in MEDLINE, EMBASE, and Clinicaltrials.gov databases up to June 28, 2021. Two independent reviewers summarized the data collected.

RESULTS

Thirteen (503 patients) of the 4.983 articles identified in the searched databases were included in our study. Most studies were published before 2010 and presented incomplete methodology descriptions. Nutritional counseling and dietary prescriptions according to the Step 1 diet of the American Heart Association (AHA) were the most common interventions. Only 2 studies evaluated changes in body weight as primary outcome. Three studies were randomized clinical trials (RCT), and none of these found the adopted interventions to demonstrate benefits.

CONCLUSION

Our scoping review evinced a scarcity of data available in the literature addressing this topic. Most studies were not controlled and presented poor methodological quality. Moreover, these studies included small sample sizes, so that the assessment of dietary interventions in these patients still lacks power for definitive conclusions. Prospective RCT should be conducted to define effective in preventing weight gain or weight loss after kidney transplant.

The Effect of Higher and Lower Protein Intakes on Nitrogen Balance in Renal Transplant Recipients with Underlying Graft Dysfunction

It is essential to determine the optimum protein intake in renal transplant recipients on steroids with renal dysfunction to maintain a neutral nitrogen balance. Our aim was to study the effect of higher (1.2 g/kg/day) and lower (0.8 g/kg/day) protein intakes on nitrogen balance, body composition, glomerular filtration rate (GFR), and proteinuria in renal transplant recipients with low estimated GFR (eGFR) (15-44 mL/min/1.73 m²). This prospective, open-labeled, randomized, cross-over, interventional study enrolled patients who were ≥4 months posttransplant with eGFR between 15 and 44 mL/min/1.73 m². Subjects were randomized to either Group 1 [Diet: proteins (1.2 g/kg/day), 35 kcal/kg/day] or Group 2 [Diet: proteins (0.8 g/kg/day) and 35 kcal/kg/day] for one month. Subjects crossed over to the other diet for 2^nd month. Body composition analysis, serum creatinine, blood urea nitrogen, serum protein, serum albumin, 24-h proteinuria, GFR measurement (24 h creatinine clearance), three-day diet recall and nitrogen balance estimation were performed at baseline and at the end of the first and 2^nd month. Statistical analysis was performed using IBM SPSS Statistics version 21. Thirty-two of 35 patients completed the study. Three-day diet recall showed that daily protein and energy consumption was 1.2 g/kg and 36.47 kcal/kg with higher and 0.94 g/kg and 31.94 kcal/kg with lower protein diets, respectively. Nitrogen balance was +3.61 g/day (P = 0.0002) with higher and +1.66 g/day with lower protein diets. A significant increase was noted in muscle mass (P = 0.0317), blood urea nitrogen (P = 0.0118), GFR (P = 0.0114), and proteinuria (P = 0.010) with a higher protein diet. Renal transplant recipients remained in positive nitrogen balance with both diets. Muscle mass and proteinuria increased significantly with a higher protein diet.

Dietary Nutrients and Cardiovascular Risk Factors among Renal Transplant Recipients

Cardiovascular disease (CVD) is the leading cause of mortality in post-renal transplant recipients (RTRs). Adequate nutrient intake is a protective factor for CVD. We examined the associations of macronutrients and micronutrients with traditional and nontraditional CVD risk factors. Conducted from September 2016 to June 2018, this cross-sectional study included 106 RTRs aged ≥18 years with a functioning allograft. Dietary intake data from 3-day dietary records were collected. Nutrient intake adequacy was defined using various instruments, including the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) guidelines. CVD risk factors were defined according to the K/DOQI guidelines. Bivariate and multivariate logistic regression models were used to analyze the associations. CVD risk was present in all patients; the lowest proportions of adequate intake were 2.8% for dietary fiber and 0.9% for calcium. Adequate nutrient intake was associated with a lower likelihood of the occurrence of traditional CVD risk factors (specifically, 1.9-31.3% for hyperlipidemia and 94.6% for diabetes mellitus). It was also associated with a lower likelihood of the occurrence of nontraditional CVD risk by 0.8% for hypophosphatemia and 34% for hyperuricemia. Adherence to dietary guidelines should be promoted among RTRs to decrease CVD risk.

Novel options for failing allograft in kidney transplanted patients to avoid or defer dialysis therapy

PURPOSE OF REVIEW

Despite improvement in short-term renal allograft survival in recent years, renal transplant recipients (RTR) have poorer long-term allograft outcomes. Allograft function slowly declines with periods of stable function similar to natural progression of chronic kidney disease in nontransplant population. Nearly all RTR transitions to failing renal allograft (FRG) period and require transition to dialysis. Conservative chronic kidney disease management before transition to end-stage renal disease is an increasingly important topic; however, there is limited data in RTR regarding how to delay dialysis initiation with conservative management.

RECENT FINDINGS

Since immunological and nonimmunological factors unique to RTR contribute to decline in allograft function, therapies to slow progression of FRG should take both sets of factors into account. Renal replacement therapy either incremental dialysis or rekidney transplantation should be explored. This required taking benefits and risks of continuing immunosuppressive medications into account when allograft nephrectomy may be necessary.

SUMMARY

FRG may benefit from various interventions to slow progression of worsening allograft function. Until there are stronger evidence to guide interventions to preserve renal function, extrapolating evidence from nontransplant patients and clinical judgment are necessary. The goal is to provide individualized care for conservative management of RTR with FRG.

Effect of an intensive nutrition intervention of a high protein and low glycemic-index diet on weight of kidney transplant recipients: study protocol for a randomized clinical trial

BACKGROUND

Excessive weight gain is commonly observed within the first year after kidney transplantation and is associated with negative outcomes, such as graft loss and cardiovascular events. The purpose of this study is to evaluate the effect of a high protein and low glycemic-index diet on preventing weight gain after kidney transplantation.

METHODS

We designed a prospective, single-center, open-label, randomized controlled study to compare the efficacy of a high protein (1.3-1.4 g/kg/day) and low-glycemic index diet versus a conventional diet (0.8-1.0 g/kg/day of protein) on preventing weight gain after kidney transplantation. A total of 120 eligible patients 2 months after transplantation will be recruited. Patients with an estimated glomerular filtration rate through the modification of diet of renal disease (MDRD) formula < 30 mL/min/1.73 m2 or urinary albumin excretion > 300 mg/24 h will be excluded. Patients' diets will be allocated through simple sequential randomization. Patients will be followed-up for 12 months with nine clinic appointments with a dietitian and the evaluations will include nutritional assessment (anthropometrics, body composition, and resting metabolic rate) and laboratory tests. The primary outcome is weight maintenance or body weight gain under 5% after 12 months. Secondary outcomes include body composition, resting metabolic rate, satiety sensation, kidney function, and other metabolic parameters.

DISCUSSION

Diets with higher protein content and lower glycemic index may lead to weight loss because of higher satiety sensation. However, there is a concern about the association of high protein intake and kidney damage. Nevertheless, there is little evidence on the impact of high protein intake on long-term kidney function outcome. Therefore, we designed a study to test if a high protein diet with low-glycemic index will be an effective and safe nutritional intervention to prevent weight gain in kidney transplant patients.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, NCT02883777 . Registered on 3 August 2016.

Urinary Urea Excretion and Long-term Outcome After Renal Transplantation

BACKGROUND

Little is known about optimal protein intake after transplantation. The aim of this study was to prospectively investigate associations of urinary urea excretion, a marker for protein intake, with graft failure and mortality in renal transplant recipients (RTR) and potential effect modification by body mass index (BMI) and estimated glomerular filtration rate (eGFR).

METHODS

Urinary urea excretion was measured in repeated 24-hr urine collections between 6 and 18 months after transplantation.

RESULTS

In total, 940 RTR were included. During 4.4 (2.3-7.8) years of follow-up for graft failure and 4.8 (2.5-8.3) years for all-cause mortality, 78 RTR developed graft failure and 158 RTR died. Urinary urea excretion was not associated with graft failure in the overall population, but was inversely associated with graft failure in RTR with BMI less than 25 kg/m (hazard ratio [HR], 0.64 [0.28-1.50] and 0.27 [0.09-0.83] for the second and third tertiles, respectively, P < 0.001), and in RTR with eGFR of 45 mL per min per 1.73 m or higher (HR, 0.34 [0.15-0.79], P = 0.015 and HR, 0.31 [0.11-0.86], P = 0.025 for the second and third tertiles, respectively), both independent of potential confounders. Compared to the first tertile, RTR in the second and third tertiles of urinary urea excretion were at a lower risk of all-cause mortality (HR, 0.47 [0.32-0.69]; P < 0.001 and HR, 0.42 [0.26-0.68]; P < 0.001, respectively), independent of potential confounders. Body mass index and eGFR did not influence this association.

CONCLUSION

Urinary urea excretion, a marker for protein intake, was inversely related to graft failure in RTR with BMI less than 25 kg/m and in RTR with an eGFR of 45 mL per min per 1.73 m or higher. In addition, urinary urea excretion was inversely related to mortality.

Causal path analyses of the association of protein intake with risk of mortality and graft failure in renal transplant recipients

The effect of a low protein intake on survival in renal transplant recipients (RTR) is unknown. A low protein intake may increase risks of malnutrition, low muscle mass, and death. We aimed to study associations of protein intake with mortality and graft failure and to identify potential intermediate factors. Protein intake was estimated from 24-h urinary urea excretion (24-h UUE). Graft failure was defined as return to dialysis or retransplantation. We used Cox regression analyses to analyze associations with outcome and potential intermediate factors in the causal path. In 604 RTR, mean ± SD 24-h UUE was 380 ± 114 mmol/24-h. During median follow-up for 7.0 yr (interquartile range: 6.2-7.5 yr), 133 RTR died and 53 developed graft failure. In univariate analyses, 24-h UUE was associated with lower risk of mortality (HR [95% CI] = 0.80 [0.69-0.94]) and graft failure (HR [95% CI] = 0.72 [0.56-0.92]). These associations were independent of potential confounders. In causal path analyses, the association of 24-h UUE with mortality disappeared after adjustment for muscle mass. Low protein intake is associated with increased risk of mortality and graft failure in RTR. Causal path analyses reveal that the association with mortality is explained by low muscle mass. These findings suggest that protein intake restriction should not be advised to RTR.

Nutrition in kidney transplantation

Organ transplantation has progressively established itself as the preferred therapy for many end-stage organ failures. However, many of these chronic diseases and their treatments can negatively affect nutritional status, leading to malnutrition and mineral deficiencies.Nutritional status is an important determinant of the clinical outcome of kidney transplant recipients.Malnutrition and obesity may represent a contraindication to transplantation in many cases and may increase the risk of postoperative complications after the transplantation. Nutritional support in kidney transplant recipients is challenging, since it must take into account the pre-transplant nutritional status, the side effects of immunosuppression, the function of the transplanted graft, the presence of infection, and the general status of the patient at the time of the transplantation.With these considerations in mind, we reviewed current literature on the impact of nutritional status on the outcome of kidney transplantation.

Dietary intake as a link between obesity, systemic inflammation, and the assumption of multiple cardiovascular and antidiabetic drugs in renal transplant recipients

We evaluated dietary intake and nutritional-inflammation status in ninety-six renal transplant recipients, 7.2 ± 5.0 years after transplantation. Patients were classified as normoweight (NW), overweight (OW), and obese (OB), if their body mass index was between 18.5 and 24.9, 25.0 and 29.9, and ≥ 30 kg/m(2), respectively. Food composition tables were used to estimate nutrient intakes. The values obtained were compared with those recommended in current nutritional guidelines. 52% of the patients were NW, 29% were OW, and 19% were OB. Total energy, fat, and dietary n-6 PUFAs intake was higher in OB than in NW. IL-6 and hs-CRP were higher in OB than in NW. The prevalence of multidrug regimen was higher in OB. In all patients, total energy, protein, saturated fatty acids, and sodium intake were higher than guideline recommendations. On the contrary, the intake of unsaturated and n-6 and n-3 polyunsaturated fatty acids and fiber was lower than recommended. In conclusion, the prevalence of obesity was high in our patients, and it was associated with inflammation and the assumption of multiple cardiovascular and antidiabetic drugs. Dietary intake did not meet nutritional recommendations in all patients, especially in obese ones, highlighting the need of a long-term nutritional support in renal transplant recipients.

Dietary protein, blood pressure and renal function in renal transplant recipients

Hypertension is highly prevalent among renal transplant recipients (RTR) and a risk factor for graft failure and cardiovascular events. Protein intake has been claimed to affect blood pressure (BP) in the general population and may affect renal function. We examined the association of dietary protein with BP and renal function in RTR. We included 625 RTR (age 53 (SD 13) years; 57% male). Protein intake was assessed with a FFQ, differentiating between animal and plant protein. BP was measured according to a strict protocol. Creatinine clearance and albuminuria were measured as renal parameters. Protein intake was 83 (SD 12) g/d, of which 63% derived from animal sources. BP was 136 (SD 17) mmHg systolic (SBP) and 83 (SD 11) mmHg diastolic (DBP). Creatinine clearance was 66 (SD 26) ml/min; albuminuria 41 (10-178) mg/24 h. An inverse, though statistically insignificant, association was found between the total protein intake and both SBP (β = - 2·22 mmHg per SD, P= 0·07) and DBP (β = - 0·48 mmHg per SD, P= 0·5). Protein intake was not associated with creatinine clearance. Although albuminuria was slightly higher in the highest tertile of animal protein intake compared with the lowest tertile (66 v. 33 mg/d, respectively, P= 0·03), linear regression analyses did not reveal significant associations between dietary protein and albuminuria. Protein intake exceeded the current recommendations. Nevertheless, within the range of protein intake in our RTR population, we found no evidence for an association of dietary protein with BP and renal function. Intervention studies focusing on different protein types are warranted to clarify their effect on BP and renal function in RTR.

Nutrition and Metabolism in Kidney Disease

Nutritional and metabolic derangements are highly prevalent in patients with chronic kidney disease (CKD) and patients on renal replacement therapy. These derangements, which can be termed uremic malnutrition, significantly affect the high morbidity and mortality rates observed in this patient population. Uremic malnutrition clearly is related to multiple factors encountered during the predialysis stage and during chronic dialysis therapy. Several preliminary studies suggested that interventions to improve the nutritional status and metabolic status of uremic patients actually may improve the expected outcome in these patients, although their long-term efficacy is not well established. It therefore is important to emphasize that uremic malnutrition is a major comorbid condition in CKD and renal replacement therapy patients, and that all efforts should be made to try to understand better and treat these conditions effectively to improve not only mortality but also the quality of life of chronically uremic patients. In this article we review the current state of knowledge in the field of nutrition and metabolism in all stages of CKD and renal replacement therapy, including kidney transplant. We also address questions that face investigators in this field and suggest where future research might be headed.

Nutrition for the post–renal transplant recipients

An adequate nutritional status may improve outcomes after renal transplantation. This review article presents the impact of major nutritional risk factors, such as malnutrition, obesity, dislipidemia, and other associated or independent metabolic complications on the results of renal transplantation. Malnutrition that exists prior to transplant may be associated with an increased risk of infection, delayed wound healing, and muscle weakness. Obesity, which may also be preexisting or developing after transplantation, can lead to adverse effects, such as poor wound healing or increased risk of cardiovascular disease, although some recent studies suggest no major consequences. Hypercholesterolemia and hypertrigliceridemia (risk factors for cardiovascular disease) are common post-renal transplantation complications. All of these possible complications may be prevented or treated through early nutritional intervention and follow-up. This article reviews important nutritional recommendations to provide guidelines for adult posttransplant recipients.

New insights into protein intake and progression of renal disease

PURPOSE OF REVIEW

For several decades, dietary protein restriction has been considered as a strategy to slow renal disease progression. Recently, a National Kidney Foundation advisory board incorporated recommendations for supervised low-protein diets into guidelines for the care of non-dialyzed patients with chronic kidney failure. Despite this consensus statement, the clinical utility of dietary modification remains controversial. This article reviews new investigations of protein intake as a mediator of renal function and physiology published since 1 October 2002.

RECENT FINDINGS

Population-level data indicate graded risk for progressive renal functional decline with increasing protein intake among women with mild renal insufficiency, and support a possible association of higher protein consumption with the risk of microalbuminuria in people with concomitant diabetes and hypertension. A link between the quantity of protein intake and the rate of renal deterioration is suggested by preliminary prospective studies among incident peritoneal dialysis patients, renal transplant recipients, and animal models of kidney disease. Varied renal consequences based on protein composition were reported in population-based studies, animal-model experiments, and animal studies of in-utero protein exposure. Clinical trial experience raises concern for the feasibility of dietary interventions in practice.

SUMMARY

New research supports the view that high-protein diets accelerate renal disease progression, suggests differential consequences based on protein source, and explores risk among defined sub-populations. Topics for future exploration include the renal impact of high-protein weight-loss regimens, implications of dietary protein quantity and type across the stages of chronic kidney disease, and translation of animal studies of prenatal nutrition to humans.