Dietary Protein Intake and Single-Nephron Glomerular Filtration Rate

Addition of bioimpedance-derived body cell mass improves performance of serum creatinine-based GFR estimation in a chronic kidney disease cohort

PURPOSE

Serum creatinine-based glomerular filtration rate (GFR) estimating equations are imprecise and systemic overestimate GFR in chronic kidney disease (CKD) populations with low muscle mass. Bioimpedance devices can measure body cell mass (BCM), a surrogate for muscle mass which has been included in a published GFR estimating equation. This BCM GFR equation is validated and compared with MDRD and CKD-EPI 2021 equations in an Indian CKD population.

METHODS

Patients with stable CKD stages 1-5 and voluntary kidney donors underwent measurement of serum creatinine, DTPA GFR and bioimpedance on the same day. BCM GFR was tested for consistency, agreement and performance with respect to DTPA GFR.

RESULTS

A total of 125 study participants were enrolled, including 106 patients with CKD (Stage 1: 8; stage 2: 32, stage 3: 42, stage 4: 20 and stage 5: 4 patients) and 19 voluntary kidney donors, with 66% males, and a mean age of 43.3 (± 16.5) years. The median bias of BCM GFR was 5.45 ml/min/1.73 m2 [95% confidence interval (CI) 4.2-8.3], absolute precision was 10.16 ml/min/1.73 m2 [95% CI 4.5-12.6], P30 was 59.1% [95% CI 50.0-67.7] and accuracy was 8.62% [95% CI 6.4-20.0]. Kappa measurement of agreement was the highest for BCM GFR-based staging (0.628 vs 0.545 for MDRD and 0.487 for CKD-EPI).

CONCLUSION

BCM-based GFR estimating equation performed better than MDRD and CKD-EPI equations in this Indian CKD population, and BCM GFR-based KDIGO staging was associated with lesser misclassification than the MDRD and CKD-EPI equations.

TRIAL REGISTRATION (PROSPECTIVE)

Clinical Trials Registry of India (CTRI/2019/11/021850).

Association Between Plant-based Diet and Kidney Function in Adults

OBJECTIVE

A plant-based diet has both antioxidant and anti-inflammatory properties. Therefore, it is hypothesized that adherence to a plant-based diet may have a positive effect on kidney function. The study aimed to determine the association between the plant-based diet index (PDI) and chronic kidney disease (CKD).

METHODS

This cross-sectional analysis used information from the Ravansar noncommunicable diseases cohort study, which included 9,746 participants between the ages of 35 and 65. By measuring the estimation glomerular filtration rate (eGFR) with the modification of diet in the renal disease equation, CKD was determined. Using a food frequency questionnaire, the PDI was computed based on food intake. To determine odds ratios (ORs), multivariable logistic regression models were utilized.

RESULTS

1,058 (10.86%) participants had CKD (eGFR<60 mL/min/1.73 m2), and the mean PDI was 54.22 ± 6.68. The mean eGFR in the group with a high PDI score was significantly higher than the group with a low PDI score (fourth quartile: 79.20 ± 0.36 vs. first quartile: 72.95 ± 0.31, P < .001). Adherence to a plant-based diet was more prevalent in those with a higher socioeconomic status (P < .001). After adjusting for potential confounders, the odds of CKD in the third and fourth quartiles of PDI were 25% (OR: 0.75; 95% confidence interval: 0.62-0.91) and 39% (OR: 0.61; 95% confidence interval: 0.48-0.78, P trend<.001) lower than the first quartile, respectively.

CONCLUSIONS

The findings of this study suggest that having a plant-based diet may prevent the prevalent CDK. However, further studies with a cohort design are recommended.

Morphometric analysis of chronicity on kidney biopsy: a useful prognostic exercise

Chronic changes on kidney biopsy specimens include increasing amounts of arteriosclerosis, glomerulosclerosis, interstitial fibrosis and tubular atrophy, enlarged nephron size, and reduced nephron number. These chronic changes are difficult to accurately assess by visual inspection but are reasonably quantified using morphometry. This review describes the various patient populations that have undergone morphometric analysis of kidney biopsies. The common approaches to morphometric analysis are described. The chronic kidney disease outcomes associated with various chronic changes by morphometry are also summarized. Morphometry enriches the characterization of chronicity on a kidney biopsy and this can supplement the pathologist's diagnosis. Artificial intelligence image processing tools are needed to automate the annotations needed for practical morphometric analysis of kidney biopsy specimens in routine clinical care.

Long-Term Renal Function in Adult Patients with Phenylketonuria

INTRODUCTION

In phenylketonuria (PKU), toxic phenylalanine (Phe) can harm other organs beyond the brain. Furthermore, the lifelong therapy of PKU consists of consumption of increased amounts of amino-acid mixture that provoke hyperfiltration in the glomeruli. Therefore, the adherence to therapy in PKU might influence the long-term kidney function in PKU patients.

METHODS

Data from 41 adult, early treated PKU patients were analyzed in this 10-year, retrospective, monocentric study. Two subgroups were created according to their therapy adherence: one with long-term blood Phe levels in the therapeutic range (<600 µmol/L), and one with suboptimal blood Phe levels. Renal function and metabolic parameters were collected over 10 years. Kidney function parameters were compared between the two groups and associations between blood Phe levels and kidney function were tested.

RESULTS

After 10 years, serum creatinine levels (p = 0.369) and estimated glomerular filtration rate (eGFR) (p = 0.723) did not change significantly from baseline in the good therapeutic group. The suboptimal therapeutic group's eGFR decreased in the same period (from 110.4 ± 14 mL/min/1.73 m2 to 94.2 ± 16 mL/min/1.73 m2, p = 0.017). At 10 years, the suboptimal therapeutic group had an increased serum creatinine level (81 ± 14.4 μmol/L vs. 71.5 ± 13 μmol/L, p = 0.038), and a decreased eGFR (94.2 ± 16 mL/min/1.73 m2 vs. 103.3 ± 13 mL/min/1.73 m2p = 0.031) compared to the good adhering group. Significant negative correlation between Phe levels and eGFR (r = -0.41, p = 0.008) was observed.

CONCLUSION

Long-term suboptimal therapy adherence in PKU patients with high blood Phe levels may lead to deterioration in kidney function.

Association between Consumption of Dietary Supplements and Chronic Kidney Disease Prevalence: Results of the Korean Nationwide Population-Based Survey

Despite the enormous global market of dietary supplements, the impact of dietary supplements on kidney disease is still unclear. Based on the National Health and Nutrition Examination Survey from 2015 to 2017, this study evaluated the association between dietary supplement and chronic kidney disease (CKD) in 13,271 Korean adults. Among the dietary supplements, vitamin and mineral intake was the highest at 61.41%, followed by omega-3 fatty acids at 11.85%, and ginseng at 7.99%. The prevalence of CKD was significantly higher in those who consumed amino acids and proteins, ginseng and red ginseng, and herbal medicine (plant extract)-berries than in those who did not. Conversely, patients who consumed probiotic supplements had a significantly lower prevalence of CKD than those who did not. In the population without CKD risk factors or history of CKD, the prevalence of CKD was high in the group consuming ginseng and red ginseng. After adjusting for covariates, the herbal medicine (plant extract)-berry group showed an independent association with CKD incidence. In conclusion, it is suggested that dietary supplements may affect kidney function. Further large-scale cohort studies are required to elucidate the exact effects of each dietary supplement on CKD.

Paradigm shift in lifestyle modification for solitary kidney after donor nephrectomy

PURPOSE OF REVIEW

Living donor kidney transplantation potentially leads to long-term complications including chronic kidney disease, end-stage kidney disease, elevated blood pressure, and pregnancy-associated hypertension. Given living donors generally do not have underlying medical conditions, lifestyle modifications, particularly dietary interventions may prevent those complications and improve their health outcomes.

RECENT FINDINGS

Glomerular hyperfiltration occurs as physiologic adaptation during an initial postdonor nephrectomy period. In the long-term, these adaptations may become pathologic consequences resulting from hyperfiltration-mediated kidney injury and ultimately secondary focal segmental glomerulosclerosis in the solitary kidney. Dietary interventions to slow a decline in kidney function include low protein intake of <0.8 g/kg/day and low sodium consumption of 2-4 g/day as well as certain health dietary patterns. There is no evidence regarding the quantity and quality of protein that can be recommended for living kidney donors and the same for sodium. Plant Dominant (PLADO) diets, Dietary Approaches to Stop Hypertension (DASH), Mediterranean, and vegetarian diets may be favorable for living kidney donors with solitary kidney but the evidence is still lacking.

SUMMARY

Although dietary interventions may provide benefits and kidney health for living kidney donors, further studies including clinical trials are required to incorporate them into clinical practice guidelines.

Novel insights in classic versus relative glomerular hyperfiltration and implications on pharmacotherapy

PURPOSE OF REVIEW

Glomerular filtration rate (GFR) assessment and its estimation (eGFR) is a long-lasting challenge in medicine and public health. Current eGFR formulae are indexed for standardized body surface area (BSA) of 1.73 m2, ignoring persons and populations wherein the ratio of BSA or metabolic rate to nephron number might be different, due to increased BSA, increased metabolic rate or reduced nephron number. These equations are based on creatinine, cystatin C or a combination of the two, which adds another confounder to eGFR assessment. Unusually high GFR values, also known as renal hyperfiltration, have not been well defined under these equations.

RECENT FINDINGS

Special conditions such as solitary kidney in kidney donors, high dietary protein intake, obesity and diabetes are often associated with renal hyperfiltration and amenable to errors in GFR estimation. In all hyperfiltration types, there is an increased intraglomerular pressure that can be physiologic, but its persistence over time is detrimental to glomerulus leading to progressive glomerular damage and renal fibrosis. Hyperfiltration might be underdiagnosed due to BSA standardization embedded in the formula. Hence, timely intervention is delayed. Reducing intraglomerular pressure in diabetes can be achieved by SGLT2 inhibitors or low protein diet to reverse the glomerulopathy process.

SUMMARY

Accurate identification of glomerular hyperfiltration as a pre-CKD condition needs accurate estimation of GFR in the above normal range should establish a threshold for timely intervention.

Update on Pathogenesis of Glomerular Hyperfiltration in Early Diabetic Kidney Disease

In the existing stages of diabetic kidney disease (DKD), the first stage of DKD is called the preclinical stage, characterized by glomerular hyperfiltration, an abnormally elevated glomerular filtration rate. Glomerular hyperfiltration is an independent risk factor for accelerated deterioration of renal function and progression of nephropathy, which is associated with a high risk for metabolic and cardiovascular disease. It is imperative to understand hyperfiltration and identify potential treatments to delay DKD progress. This paper summarizes the current mechanisms of hyperfiltration in early DKD. We pay close attention to the effect of glucose reabsorption mediated by sodium-glucose cotransporters and renal growth on hyperfiltration in DKD patients, as well as the mechanisms of nitric oxide and adenosine actions on renal afferent arterioles via tubuloglomerular feedback. Furthermore, we also focus on the contribution of the atrial natriuretic peptide, cyclooxygenase, renin-angiotensin-aldosterone system, and endothelin on hyperfiltration. Proposing potential treatments based on these mechanisms may offer new therapeutic opportunities to reduce the renal burden in this population.

Kidney disease risk factors do not explain impacts of low dietary protein on kidney function and structure

The kidneys balance many byproducts of the metabolism of dietary components. Previous studies examining dietary effects on kidney health are generally of short duration and manipulate a single macronutrient. Here, kidney function and structure were examined in C57BL/6J mice randomized to consume one of a spectrum of macronutrient combinations (protein [5%–60%], carbohydrate [20%–75%], and fat [20%–75%]) from weaning to late-middle age (15 months). Individual and interactive impacts of macronutrients on kidney health were modeled. Dietary protein had the greatest influence on kidney function, where chronic low protein intake decreased glomerular filtration rates and kidney mass, whereas it increased kidney immune infiltration and structural injury. Kidney outcomes did not align with cardiometabolic risk factors including glucose intolerance, overweight/obesity, dyslipidemia, and hypertension in mice with chronic low protein consumption. This study highlights that protein intake over a lifespan is an important determinant of kidney function independent of cardiometabolic changes.

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Chronic high macronutrient intake from any source increases kidney function (GFR)

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Low protein intake led to greater kidney tubular structural injury and inflammation

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Lower protein intake decreased kidney mass and glomerular filtration capacity

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Kidney outcomes did not align with longevity or cardiometabolic outcomes

Chronic Kidney Disease: Role of Diet for a Reduction in the Severity of the Disease

Chronic kidney disease affects ~37 million adults in the US, and it is often undiagnosed due to a lack of apparent symptoms in early stages. Chronic kidney disease (CKD) interferes with the body's physiological and biological mechanisms, such as fluid electrolyte and pH balance, blood pressure regulation, excretion of toxins and waste, vitamin D metabolism, and hormonal regulation. Many CKD patients are at risk of hyperkalemia, hyperphosphatemia, chronic metabolic acidosis, bone deterioration, blood pressure abnormalities, and edema. These risks may be minimized, and the disease's progression may be slowed through careful monitoring of protein, phosphorus, potassium, sodium, and calcium, relieving symptoms experienced by CKD patients. In this review, the current Kidney Disease Outcomes Quality Initiative (KDOQI) recommendations are highlighted, reflecting the 2020 update, including explanations for the pathophysiology behind the recommendations. The Dietary Approaches to Stop Hypertension, the Mediterranean diet, and the whole foods plant-based diet are currently being examined for their potential role in delaying CKD progression. Biological explanations for why the whole foods plant-based diet may benefit CKD patients compared to diets that include animal products are examined. Strong evidence continues to support the importance of diet meeting the daily requirement in the prevention and progression of kidney disease, and medical nutrition therapy with a registered dietitian is a critical aspect in medical intervention for CKD.