Dietary acid intake and kidney disease progression in the elderly

Dietary acid load in health and disease

Maintaining an appropriate acid-base equilibrium is crucial for human health. A primary influencer of this equilibrium is diet, as foods are metabolized into non-volatile acids or bases. Dietary acid load (DAL) is a measure of the acid load derived from diet, taking into account both the potential renal acid load (PRAL) from food components like protein, potassium, phosphorus, calcium, and magnesium, and the organic acids from foods, which are metabolized to bicarbonate and thus have an alkalinizing effect. Current Western diets are characterized by a high DAL, due to large amounts of animal protein and processed foods. A chronic low-grade metabolic acidosis can occur following a Western diet and is associated with increased morbidity and mortality. Nutritional advice focusing on DAL, rather than macronutrients, is gaining rapid attention as it provides a more holistic approach to managing health. However, current evidence for the role of DAL is mainly associative, and underlying mechanisms are poorly understood. This review focusses on the role of DAL in multiple conditions such as obesity, cardiovascular health, impaired kidney function, and cancer.

Dietary acid load and the risk of events of mortality and kidney replacement therapy in people with chronic kidney disease: the Progredir Cohort Study

BACKGROUND/OBJECTIVES

The association between dietary acid load (DAL) and chronic kidney disease (CKD) progression remains controversial. Also, there is a gap in the literature on the association between DAL and mortality. In this study, we evaluated the association between NEAP (net endogenous acid production) and PRAL (potential renal acid load) and the risk of events of all-cause mortality and kidney replacement therapy (KRT) in people with CKD.

SUBJECTS/METHODS

We included 442 patients (250 diabetics) from the Progredir Cohort Study, based in São Paulo, Brazil. We estimated NEAP and PRAL from dietary intake. Events of death before KRT and KRT were ascertained after a median follow-up of 5.8 and 5.1 years, respectively. Cox proportional hazards regression, Weibull regression, and competing risk models were performed.

RESULTS

Median NEAP and PRAL were 49.5 and 4.8 mEq/d. There were 200 deaths and 75 KRT events. Neither NEAP nor PRAL were associated with mortality or KRT when all participants were analyzed. After stratification for diabetes, both estimates were positively related to the risk of KRT even after adjustment for age, sex, weight status, glomerular filtration rate, serum bicarbonate, and intakes of protein, phosphorus, and energy (HR 1.31; 95% CI 1.07, 1.60 for NEAP, and HR 1.27; 95% CI 1.04, 1.57 for every 10 mEq/d increments). Competing risk analyses confirmed these findings.

CONCLUSIONS

DAL estimates were associated with the risk of KRT in people with CKD and diabetes but not in non-diabetics. There was no association between all-cause mortality and DAL.

Chronic Sub-Clinical Systemic Metabolic Acidosis - A Review with Implications for Clinical Practice

When arterial serum pH remains near the lower pH limit of 7.35 for protracted periods of time, a low-grade, sub-clinical form of acidosis results, referred to in this review as chronic, sub-clinical, systemic metabolic acidosis (CSSMA). This narrative review explores the scientific basis for CSSMA, its consequences for health, and potential therapeutic interventions. The major etiology of CSSMA is the shift away from the ancestral, alkaline diet which was rich in fruit and vegetables, toward the contemporary, acidogenic 'Westernized' diet characterized by higher animal protein consumption and lack of base forming minerals. Urine pH is reduced with high dietary acid load and may be a convenient marker of CSSMA. Evidence suggests further that CSSMA negatively influences cortisol levels potentially contributing significantly to the pathophysiology thereof. Both CSSMA and high dietary acid load are associated with the risk and prognosis of various chronic diseases. Clinical trials show that CSSMA can be addressed successfully through alkalizing the diet by increasing fruit and vegetable intake and/or supplementing with alkaline minerals. This review confirms the existence of a significant body of evidence regarding this low-grade form of acidosis as well as evidence to support its diverse negative implications for health, and concludes that CSSMA is a condition warranting further research.

Machine Learning Models Predicting Cardiovascular and Renal Outcomes and Mortality in Patients with Hyperkalemia

Hyperkalemia is associated with increased risks of mortality and adverse clinical outcomes. The treatment of hyperkalemia often leads to the discontinuation or restriction of beneficial but potassium-increasing therapy such as renin-angiotensin-aldosterone inhibitors (RAASi) and high-potassium diet including fruits and vegetables. To date, limited evidence is available for personalized risk evaluation in this heterogeneous and multifactorial pathophysiological condition. We developed risk prediction models using extreme gradient boosting (XGB), multiple logistic regression (LR), and deep neural network. Models were derived from a retrospective cohort of hyperkalemic patients with either heart failure or chronic kidney disease stage ≥3a from a Japanese nationwide database (1 April 2008−30 September 2018). Studied outcomes included all-cause death, renal replacement therapy introduction (RRT), hospitalization for heart failure (HHF), and cardiovascular events within three years after hyperkalemic episodes. The best performing model was further validated using an external cohort. A total of 24,949 adult hyperkalemic patients were selected for model derivation and internal validation. A total of 1452 deaths (16.6%), 887 RRT (10.1%), 1,345 HHF (15.4%), and 621 cardiovascular events (7.1%) were observed. XGB outperformed other models. The area under receiver operator characteristic curves (AUROCs) of XGB vs. LR (95% CIs) for death, RRT, HHF, and cardiovascular events were 0.823 (0.805−0.841) vs. 0.809 (0.791−0.828), 0.957 (0.947−0.967) vs. 0.947 (0.936−0.959), 0.863 (0.846−0.880) vs. 0.838 (0.820−0.856), and 0.809 (0.784−0.834) vs. 0.798 (0.772−0.823), respectively. In the external dataset including 86,279 patients, AUROCs (95% CIs) for XGB were: death, 0.747 (0.742−0.753); RRT, 0.888 (0.882−0.894); HHF, 0.673 (0.666−0.679); and cardiovascular events, 0.585 (0.578−0.591). Kaplan−Meier curves of the high-risk predicted group showed a statistically significant difference from that of the low-risk predicted groups for all outcomes (p < 0.005; log-rank test). These findings suggest possible use of machine learning models for real-world risk assessment as a guide for observation and/or treatment decision making that may potentially lead to improved outcomes in hyperkalemic patients while retaining the benefit of life-saving therapies.

Longitudinal association of dietary acid load with kidney function decline in an older adult population with metabolic syndrome

Background

Diets high in acid load may contribute to kidney function impairment. This study aimed to investigate the association between dietary acid load and 1-year changes in glomerular filtration rate (eGFR) and urine albumin/creatinine ratio (UACR).

Methods

Older adults with overweight/obesity and metabolic syndrome (mean age 65 ± 5 years, 48% women) from the PREDIMED-Plus study who had available data on eGFR (n = 5,874) or UACR (n = 3,639) at baseline and after 1 year of follow-up were included in this prospective analysis. Dietary acid load was estimated as potential renal acid load (PRAL) and net endogenous acid production (NEAP) at baseline from a food frequency questionnaire. Linear and logistic regression models were fitted to evaluate the associations between baseline tertiles of dietary acid load and kidney function outcomes. One year-changes in eGFR and UACR were set as the primary outcomes. We secondarily assessed ≥ 10% eGFR decline or ≥10% UACR increase.

Results

After multiple adjustments, individuals in the highest tertile of PRAL or NEAP showed higher one-year changes in eGFR (PRAL, β: -0.64 ml/min/1.73 m2; 95% CI: -1.21 to -0.08 and NEAP, β: -0.56 ml/min/1.73 m2; 95% CI: -1.13 to 0.01) compared to those in the lowest category. No associations with changes in UACR were found. Participants with higher levels of PRAL and NEAP had significantly higher odds of developing ≥10% eGFR decline (PRAL, OR: 1.28; 95% CI: 1.07-1.54 and NEAP, OR: 1.24; 95% CI: 1.03-1.50) and ≥10 % UACR increase (PRAL, OR: 1.23; 95% CI: 1.04-1.46) compared to individuals with lower dietary acid load.

Conclusions

Higher PRAL and NEAP were associated with worse kidney function after 1 year of follow-up as measured by eGFR and UACR markers in an older Spanish population with overweight/obesity and metabolic syndrome.

The Importance of Recognizing and Addressing the Spectrum of Acid Stress

Acid accumulation sufficient to reduce plasma bicarbonate concentration, thereby recognized as chronic metabolic acidosis, harms bones and muscles and appears to enhance progression of CKD. Evolving evidence supports that progressive acid accumulation that is not enough to cause chronic metabolic acidosis nevertheless has deleterious effects. Measurable acid retention without reduced plasma bicarbonate concentration, called eubicarbonatemic acidosis, also appears to cause kidney injury and exacerbate CKD progression. Furthermore, chronic engagement of mechanisms to mitigate the ongoing acid challenge of net acid-producing diets of developed societies also appears to be deleterious, including for kidney health. This review challenges clinicians to consider the growing evidence for a spectrum of acid-accumulation disorders that include lesser degrees of acid accumulation than metabolic acidosis yet are harmful. Further research will develop clinically useful tools to identify individuals suffering from these earlier stages of acid stress and determine if the straightforward and comparatively inexpensive intervention of dietary acid reduction relieves or eliminates the harm they appear to cause.

Dietary acid load and risk of cardiovascular disease: a prospective population-based study

BACKGROUND AND AIM

Considering the inconsistencies in the cardiovascular effects of dietary acid load and the impact of dietary acidity on the acid-base homeostasis within the body, we aimed to assess the association of dietary acid load and the risk of cardiovascular disease (CVD) in a prospective community-based study.

MATERIALS AND METHODS

Participants (n = 2369) free of CVD at baseline (2006-2008) were included from the Tehran Lipid and Glucose Study (TLGS) and followed up for a mean of 6.7 ± 1.4 years. Dietary intakes of the participants were assessed using a semi-quantitative food frequency questionnaire (FFQ). The dietary acid load was evaluated by Potential Renal Acid Load (PRAL) and Net Endogenous Acid Production (NEAP) scores. Both scores have used the macronutrient and micronutrient data of the Food Frequency Questionnaires. Multivariate Cox proportional hazard regression models were used to estimate the 6-years incident risk of CVDs across tertiles of PRAL and NEAP scores.

RESULTS

Mean age and body mass index of participants were 38.5 ± 13.3 years and 26.6 ± 4.8 kg/m² at baseline. Within 6.7 ± 1.4 years of follow-up, 79 cases of cardiovascular events were reported. NEAP was significantly associated with the incidence of CVDs (HRs = 0.50, CI 0.32-0.96; P for trend = 0.032); however, after adjusting for potential confounders, no significant associations were observed between PRAL and NEAP scores and the risk of CVDs.

CONCLUSIONS

This study failed to obtain independent associations between dietary acid load and the incidence of CVDs among an Asian population.

Adherence to Healthy Dietary Patterns and Risk of CKD Progression and All-Cause Mortality: Findings From the CRIC (Chronic Renal Insufficiency Cohort) Study

RATIONALE & OBJECTIVE

Current dietary guidelines recommend that patients with chronic kidney disease (CKD) restrict individual nutrients, such as sodium, potassium, phosphorus, and protein. This approach can be difficult for patients to implement and ignores important nutrient interactions. Dietary patterns are an alternative method to intervene on diet. Our objective was to define the associations of 4 healthy dietary patterns with risk for CKD progression and all-cause mortality among people with CKD.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

2,403 participants aged 21 to 74 years with estimated glomerular filtration rates of 20 to 70mL/min/1.73m2 and dietary data in the Chronic Renal Insufficiency Cohort (CRIC) Study.

EXPOSURES

Healthy Eating Index-2015, Alternative Healthy Eating Index-2010, alternate Mediterranean diet (aMed), and Dietary Approaches to Stop Hypertension (DASH) diet scores were calculated from food frequency questionnaires.

OUTCOMES

(1) CKD progression defined as≥50% estimated glomerular filtration rate decline, kidney transplantation, or dialysis and (2) all-cause mortality.

ANALYTICAL APPROACH

Cox proportional hazards regression models adjusted for demographic, lifestyle, and clinical covariates to estimate hazard ratios (HRs) and 95% CIs.

RESULTS

There were 855 cases of CKD progression and 773 deaths during a maximum of 14 years. Compared with participants with the lowest adherence, the most highly adherent tertile of Alternative Healthy Eating Index-2010, aMed, and DASH had lower adjusted risk for CKD progression, with the strongest results for aMed (HR, 0.75; 95% CI, 0.62-0.90). Compared with participants with the lowest adherence, the highest adherence tertiles for all scores had lower adjusted risk for all-cause mortality for each index (24%-31% lower risk).

LIMITATIONS

Self-reported dietary intake.

CONCLUSIONS

Greater adherence to several healthy dietary patterns is associated with lower risk for CKD progression and all-cause mortality among people with CKD. Guidance to adopt healthy dietary patterns can be considered as a strategy for managing CKD.

Low serum total CO2 and its association with mortality in patients being followed up in the nephrology outpatients clinic

Large-scale studies have not been conducted to assess whether serum hypobicarbonatemia increases the risk for kidney function deterioration and mortality among East-Asians. We aimed to determine the association between serum total CO₂ (TCO₂) concentrations measured at the first outpatient visit and clinical outcomes. In this multicenter cohort study, a total of 42,231 adult nephrology outpatients from 2001 to 2016 were included. End-stage renal disease (ESRD) patients on dialysis within 3 months of the first visit were excluded. Instrumental variable (IV) was used to define regions based on the proportion of patients with serum TCO₂ < 22 mEq/L. The crude mortality rate was 12.2% during a median 77.0-month follow-up period. The Cox-proportional hazard regression model adjusted for initial kidney function, alkali supplementation, and the use of diuretics demonstrated that low TCO₂ concentration was not associated with progression to ESRD, but significantly increased the risk of death. The IV analysis also confirmed a significant association between initial TCO₂ concentration and mortality (HR 0.56; 95% CI 0.49–0.64). This result was consistently significant regardless of the underlying renal function. In conclusion, low TCO₂ levels are significantly associated with mortality but not with progression to ESRD in patients with ambulatory care.

KDOQI Clinical Practice Guideline for Nutrition in CKD: 2020 Update

The National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (KDOQI) has provided evidence-based guidelines for nutrition in kidney diseases since 1999. Since the publication of the first KDOQI nutrition guideline, there has been a great accumulation of new evidence regarding the management of nutritional aspects of kidney disease and sophistication in the guidelines process. The 2020 update to the KDOQI Clinical Practice Guideline for Nutrition in CKD was developed as a joint effort with the Academy of Nutrition and Dietetics (Academy). It provides comprehensive up-to-date information on the understanding and care of patients with chronic kidney disease (CKD), especially in terms of their metabolic and nutritional milieu for the practicing clinician and allied health care workers. The guideline was expanded to include not only patients with end-stage kidney disease or advanced CKD, but also patients with stages 1-5 CKD who are not receiving dialysis and patients with a functional kidney transplant. The updated guideline statements focus on 6 primary areas: nutritional assessment, medical nutrition therapy (MNT), dietary protein and energy intake, nutritional supplementation, micronutrients, and electrolytes. The guidelines primarily cover dietary management rather than all possible nutritional interventions. The evidence data and guideline statements were evaluated using Grading of Recommendations, Assessment, Development and Evaluation (GRADE) criteria. As applicable, each guideline statement is accompanied by rationale/background information, a detailed justification, monitoring and evaluation guidance, implementation considerations, special discussions, and recommendations for future research.

Plant-based diets to manage the risks and complications of chronic kidney disease

Traditional dietary recommendations for patients with chronic kidney disease (CKD) focus on the quantity of nutrients consumed. Without appropriate dietary counselling, these restrictions can result in a low intake of fruits and vegetables and a lack of diversity in the diet. Plant nutrients and plant-based diets could have beneficial effects in patients with CKD: increased fibre intake shifts the gut microbiota towards reduced production of uraemic toxins; plant fats, particularly olive oil, have anti-atherogenic effects; plant anions might mitigate metabolic acidosis and slow CKD progression; and as plant phosphorus has a lower bioavailability than animal phosphorus, plant-based diets might enable better control of hyperphosphataemia. Current evidence suggests that promoting the adoption of plant-based diets has few risks but potential benefits for the primary prevention of CKD, as well as for delaying progression in patients with CKD G3-5. These diets might also help to manage and prevent some of the symptoms and metabolic complications of CKD. We suggest that restriction of plant foods as a strategy to prevent hyperkalaemia or undernutrition should be individualized to avoid depriving patients with CKD of these potential beneficial effects of plant-based diets. However, research is needed to address knowledge gaps, particularly regarding the relevance and extent of diet-induced hyperkalaemia in patients undergoing dialysis.

Ameliorating Chronic Kidney Disease Using a Whole Food Plant-Based Diet

Novel approaches to ameliorating chronic kidney disease (CKD) are warranted as most patients are undiagnosed until they begin displaying symptoms of kidney failure. There is increasing evidence that a whole food plant-based (WFPB) diet may offer benefits that slow the progression of CKD, decrease the incidence cardiovascular disease, decrease rates of diabetes and obesity, and reduce inflammation and cholesterol, which in turn can delay kidney failure and the initiation of dialysis. While animal-based protein ingestion promotes an acidic environment, inflammation and renal hyperfiltration, study authors report plant-based protein can be alkaline-producing and anti-inflammatory and can contain renoprotective properties. Although there may be benefits to adopting a WFPB diet, macronutrient and micronutrient content should be carefully considered and adjusted to avoid malnutrition in CKD patients. Further research needs to be done in order to establish the biological plausibility and feasibility of a WFPB in individuals with diagnosed CKD.

Higher estimated net endogenous acid production with lower intake of fruits and vegetables based on a dietary survey is associated with the progression of chronic kidney disease

Background

Dietary acid load has been suggested to mediate the progression of chronic kidney disease (CKD). However, it is unclear what kinds of foods are actually associated with dietary acid load in patients with CKD. The self-administered diet history questionnaire (DHQ), which semi-quantitatively assesses the dietary habits of Japanese individuals through 150 question items, can estimate average daily intake of various foods and nutrients during the previous month. Using the DHQ, we investigated the association of dietary acid load with CKD progression. We also analyzed the kinds of food that significantly affect dietary acid load.

Methods

Subjects were 96 outpatients with CKD (average estimated glomerular filtration rate [eGFR], 53.0 ± 18.1 ml/min/1.73 m²) at Niigata University Hospital, who had completed the DHQ in 2011. We calculated net endogenous acid production (NEAP) from potassium and protein intake evaluated by the DHQ in order to assess dietary acid load. CKD progression was assessed by comparing eGFR between 2008 and 2014.

Results

NEAP was not correlated with protein intake (r = 0.088, p = 0.398), but was negatively correlated with potassium intake (r = − 0.748, p < 0.001). Reduction in eGFR from 2008 to 2014 was estimated to be significantly greater in patients with higher NEAP (NEAP > 50.1 mEq/day, n = 45) than in those with lower NEAP (NEAP ≤50.1 mEq/day, n = 50) by 5.9 (95% confidence interval [95%CI], 0.1 to 11.6) ml/min/1.73 m². According to multiple logistic regression analysis, higher NEAP was significantly associated with lower intake of fruits (odds ratio [OR], 6.454; 95%CI, 2.19 to 19.00), green and yellow vegetables (OR, 5.18; 95%CI, 1.83 to14.66), and other vegetables (OR, 3.87; 95%CI, 1.29 to 11.62).

Conclusions

Elevated NEAP could be a risk factor for CKD progression. Low intake of fruits and vegetables would increase dietary acid load and might affect the progression of renal dysfunction in Japanese CKD patients.

APOL1, Acid Load, and CKD Progression

INTRODUCTION

High dietary acid load and metabolic acidosis are associated with an accelerated decline in kidney function and may contribute to the observed heterogeneity in end-stage renal disease (ESRD) risk according to APOL1 genotype. Our objective was to examine the associations of metabolic acidosis and dietary acid load with kidney disease progression, according to APOL1 genotype, among individuals with chronic kidney disease (CKD).

METHODS

We studied 1048 African American participants in the Chronic Renal Insufficiency Cohort. Metabolic acidosis was defined as blood levels of serum bicarbonate less than 22 mEq/L, and dietary acid load was quantified by potential renal acid load (PRAL) using data from the Diet Health Questionnaire. APOL1 status was defined as having 2 risk variants, consisting of either possible combination of the G1 and G2 risk alleles. We tested associations of APOL1 and dietary and metabolic acidosis with CKD progression, defined as time to ESRD or 50% decline in eGFR.

RESULTS

During a median follow-up period of 7 years, 379 participants had an incident CKD progression event (6.4 events per 100 person-years). After full adjustment, among participants with 2 APOL1 variants, the analysis failed to detect an association between metabolic acidosis or dietary acid load and CKD progression (hazard ratio [HR], 1.03; 95% confidence interval [CI], 0.96-1.11 per 1 mEq/L higher serum bicarbonate and an HR, 1.03; 95% CI, 0.92-1.15 per 10 mEq/L higher PRAL). Similar associations were noted among participants without the APOL1 high-risk genotype.

CONCLUSION

In a population at high risk of developing ESRD, metabolic acidosis and dietary acid load were not associated with CKD progression.

Association of estimated dietary acid load with albuminuria in Japanese adults: a cross-sectional study

Background

Acid-base imbalance might promote the progression of chronic kidney disease (CKD), but whether nutrient-derived dietary acid load increases the risk of albuminuria or even high normoalbuminuria is unclear.

Methods

A Japanese cohort comprising 3250 men and 3434 women aged 40–97 years with urine albumin-to-creatinine ratio (ACR) < 33.9 mg/mmol or estimated glomerular filtration rate ≥ 15 ml/min/1.73 m² were assessed. We performed a cross-sectional evaluation of the association between net endogenous acid production (NEAP), estimated as dietary protein to potassium content ratio, and the presence of high normoalbuminuria (ACR: 1.13–3.38 mg/mmol) or microalbuminuria.

Results

Median NEAP was 43.4 (interquartile range (IQR): 34.2–53.4) mEq/day in men and 35.0 (IQR: 27.7–43.6) mEq/day in women. Median ACR was 1.11 (IQR: 0.57–2.49) mg/mmol in men and 1.47 (IQR: 0.82–2.83) mg/mmol in women. In multivariate analysis, the adjusted odds ratio of the highest versus lowest NEAP quartile for microalbuminuria was 1.47 (95% confidence interval (CI): 1.08–1.99) in men and 1.54 (95% CI: 1.11–2.14) in women. For high normoalbuminuria or microalbuminuria, the adjusted odds ratio was 1.28 (95% CI: 1.02–1.59) in men and 1.39 (95% CI: 1.11–1.74) in women. From nutrient composition analysis, subjects with the highest potassium intake, but not protein intake, had lower adjusted odds ratios for the presence of microalbuminuria than those in the lowest quartile for potassium intake.

Conclusions

Higher NEAP was associated with albuminuria and its association might negatively relate to potassium intake in an adult Japanese population.

Dietary acid load, kidney function and risk of chronic kidney disease: A systematic review and meta-analysis of observational studies

Aim: Study findings examining the association between dietary acid load (DAL), kidney function and risk of chronic kidney disease (CKD) are inconsistent and there has been no meta-analysis on the relationship between DAL, kidney function and risk of CKD, hence we investigated this association in this paper. Methods: PubMed, ISI web of science and Scopus were searched up to January 2018 to identify all relevant articles. Effect sizes of eligible studies were pooled in random- effect model using the Der Simonian-Laird method. The I² index was used to assess the amount of heterogeneity. Result: Twenty three studies with 200092 subjects were included. Meta-analysis of 9 observational studies showed that DAL had a positive significant association with risk of CKD (1.31; 95% CI: 1.06, 1.62; P = 0.011). Furthermore, increased DAL can decrease urine pH (-0.47; 95% CI: -0.85, -0.08; P = 0.017) significantly. Subgroup analysis could not identify the sources of heterogeneity about the association of DAL and risk of CKD. However, it showed the method of measurement was the source of heterogeneity about the association of DAL and urine pH (24 h urine pH: -0.62; 95% CI: -0.70, -0.54; P < 0.0001; Fasting urine pH: -0.08; 95% CI: -0.18, 0.02; P = 0.111). Conclusion: Our study showed that DAL can increase the risk of CKD and have an inverse association with urine pH.

Poor accordance to a DASH dietary pattern is associated with higher risk of ESRD among adults with moderate chronic kidney disease and hypertension

The Dietary Approaches to Stop Hypertension (DASH) diet lowers blood pressure, an important risk factor for chronic kidney disease (CKD) and end-stage renal disease (ESRD). However, it is unclear whether adherence to a DASH diet confers protection against future ESRD, especially among those with pre-existing CKD and hypertension. We examined whether a DASH diet is associated with lower risk of ESRD among 1,110 adults aged ≥ 20 years with hypertension and CKD (estimated glomerular filtration rate, eGFR 30-59 ml/min/1.73 m²) enrolled in the National Health and Nutrition Examination Survey (1988-1994). Baseline DASH diet accordance score was assessed using a 24-hour dietary recall questionnaire. ESRD was ascertained by linkage to the U.S. Renal Data System registry. We used the Fine-Gray competing risks method to estimate the relative hazard (RH) for ESRD after adjusting for sociodemographics, clinical and nutritional factors, eGFR, and albuminuria. Over a median follow-up of 7.8 years, 18.4% of subjects developed ESRD. Compared to the highest quintile of DASH diet accordance, there was a greater risk of ESRD among subjects in quintiles 1 (RH=1.7; 95% CI 1.1-2.7) and 2 (RH 2.2; 95% CI 1.1-4.1). Significant interactions were observed with diabetes status and race/ethnicity, with the strongest association between DASH diet adherence and ESRD risk observed in individuals with diabetes and in non-Hispanic blacks. Low accordance to a DASH diet is associated with greater risk of ESRD in adults with moderate CKD and hypertension, particularly in non-Hispanic blacks and persons with diabetes.

Sociodemographic and Kidney Disease Correlates of Nutrient Intakes Among Urban African Americans With Uncontrolled Hypertension

OBJECTIVE

The objective of this study was to determine the association between sociodemographic factors and intakes of 4 nutrients and associations between intakes and markers of kidney disease to identify opportunities to improve outcomes among clinically high-risk African Americans.

DESIGN AND METHODS

We conducted a cross-sectional study of baseline data from the Achieving Blood Pressure Control Together study, a randomized controlled trial of 159 African Americans (117 females) with uncontrolled hypertension in Baltimore MD. To determine the association between sociodemographic factors and nutrient intakes, we constructed linear and logistic regression models. Using logistic regression, we determined the association between below-median nutrient intakes and kidney disease. Our outcomes of interest were daily intakes of vitamin C, magnesium, dietary fiber, and potassium as estimated by the Block Fruit-Vegetable-Fiber Screener and kidney disease defined as estimated glomerular filtration rate <60 mL/min per 1.73 m2 or urinary albumin-to-creatinine ratio >=30 mg/g.

SETTING AND SUBJECTS

Baseline data from the Achieving Blood Pressure Control Together study, a randomized controlled trial of 159 African Americans (117 females) with uncontrolled hypertension, were obtained.

METHODS

To determine the association between sociodemographic factors and nutrient intakes, we constructed linear and logistic regression models. Using logistic regression, we determined the association between below-median nutrient intakes and kidney disease.

MAIN OUTCOME MEASURES

Our outcomes of interest were daily intakes of vitamin C, magnesium, dietary fiber, and potassium as estimated by the Block Fruit-Vegetable-Fiber Screener and kidney disease defined as estimated glomerular filtration rate <60 mL/min per 1.73 m² or urinary albumin-to-creatinine ratio ≥30 mg/g.

RESULTS

Overall, compared to Institute of Medicine recommendations, participants had lower intakes of magnesium, fiber, and potassium but higher vitamin C intakes. For females, sociodemographic factors that significantly associated with lower intake of the 4 nutrients were older age, obesity, lower health numeracy, and lesser educational attainment. For males, none of the sociodemographic factors were significantly associated with nutrient intakes. Below-median intake was significantly associated with albumin-to-creatinine ratio ≥30 (adjusted odds ratio [95% confidence interval]: 3.4 [1.5, 7.8] for vitamin C; 3.6 [1.6, 8.4] for magnesium; 2.9 [1.3, 6.5] for fiber; 3.6 [1.6, 8.4] for potassium), but not with estimated glomerular filtration rate <60.

CONCLUSION

African Americans with uncontrolled hypertension may have low intakes of important nutrients, which could increase their risk of chronic kidney disease. Tailored dietary interventions for African Americans at high risk for chronic kidney disease may be warranted.

Intracellular protons accelerate aging and switch on aging hallmarks in mice

Diet-induced metabolic acidosis is associated with the impairment of bone metabolism and an increased risk of a number of chronic noncommunicable diseases, such as type 2 diabetes mellitus and hypertension. The serum bicarbonate level is an independent predictor of chronic kidney disease progression. We investigated whether proton accelerates aging by analyzing both coupling factor 6-overexpressing transgenic (TG) and high salt-fed mice which display sustained intracellular acidosis, due to enhanced proton import through ecto-F₁ F_o complex and/or reduced proton export through Na⁺ -K⁺ ATPase inhibition. Both types of mice displayed shortened lifespan and early senescence-associated phenotypes such as signs of hair greying and alopecia, weight loss, and/or reduced organ mass. In chronic intracellular acidosis mice, autophagy was impaired by regression of Atg7, an increase in nuclear acetylated LC3 II, and acetylation of Atg7. The increase in histone 3 trimethylation at lysine 4 (H3K4me3) and H4K20me3 and the decrease in H3K9me3 and H3K27me3 were observed in the heart and kidney obtained from both TG and high salt-fed mice. The decrease in lamin A/C, emerin, and heterochromatin protein 1α without changes in barrier-to-autointegration factor and high-mobility group box 1 was confirmed in TG and high salt-fed mice. Suppression of nuclear histone deacetylase 3-emerin system is attributable to epigenetic regression of Atg7 and H4K5 acetylation. These findings will shed light on novel aging and impaired autophagy mechanism, and provide implications in a target for antiaging therapy.

[Dietary acid load: A novel target for the nephrologist?]

The acid production of endogenous origin depends mainly on the metabolism of the food and varies with the nature of these. Of the order of 1mEq/kg/day for contemporary food in industrialized countries, it is reduced by more than one third among vegetarians and close to neutrality among vegans. The dietary acid load is eliminated by the normal kidneys, thus maintaining the acid-base equilibrium. In the setting of CKD, it will overflow the capacities of the nephrons, generating a retention of H+ ions, promoting subclinical acidosis. This tissue retention of H+ ions was confirmed by direct techniques in animal models and indirect techniques in humans. The systemic retention of H+ ions and the accompanying compensatory mechanisms have negative consequences on bone tissue, skeletal muscle, cardiovascular risk and renal function. In the animal, the substitution of casein (acid) by soy (alkaline) prevents metabolic acidosis and slows the progression of renal insufficiency. In man, various prospective studies have confirmed that the risk of renal insufficiency was positively correlated with the dietary acid load. Conversely, bicarbonate supplementation and/or a diet enriched with fruits and vegetables, have a favorable effect on renal insufficiency, including in subjects with normal bicarbonate. These results lead to reconsider the K/DOQI recommendations to correct acidosis when the bicarbonate level falls below 22mEq/L, since tissue retention of H+ ions and its negative consequences appear at higher or even normal levels of bicarbonates.

Potential applications of a new short food frequency questionnaire for CKD patients

Diet is among the most modifiable risk factors for chronic kidney disease (CKD) progression. Studies of beneficial dietary patterns for persons with CKD have largely utilized dietary assessment measures developed in individuals without CKD. In BMC Nephrology, Affret et al. report on their study of the reproducibility of a newly developed short 49-item food frequency questionnaire (SFFQ) adapted to patients with CKD. Here, we discuss potential applications of this SFFQ, towards better understanding of which dietary patterns portend the most favorable outcomes in CKD.

Diet-Induced Low-Grade Metabolic Acidosis and Clinical Outcomes: A Review

Low-grade metabolic acidosis is a condition characterized by a slight decrease in blood pH, within the range considered normal, and feeding is one of the main factors that may influence the occurrence of such a condition. The excessive consumption of acid precursor foods (sources of phosphorus and proteins), to the detriment of those precursors of bases (sources of potassium, calcium, and magnesium), leads to acid-base balance volubility. If this condition occurs in a prolonged, chronic way, low-grade metabolic acidosis can become significant and predispose to metabolic imbalances such as kidney stone formation, increased bone resorption, reduced bone mineral density, and the loss of muscle mass, as well as the increased risk of chronic diseases such as type 2 diabetes mellitus, hypertension, and non-alcoholic hepatic steatosis. Considering the increase in the number of studies investigating the influence of diet-induced metabolic acidosis on clinical outcomes, this review gathers the available evidence evaluating the association of this disturbance and metabolic imbalances, as well as related mechanisms. It is necessary to look at the western dietary pattern of most countries and the increasing incidence of non-comunicable diseases for the balance between fruit and vegetable intake and the appropriate supply of protein, mainly from animal sources, so that it does not exceed the daily recommendations.

Dietary Acid Load is Associated With Serum Bicarbonate but not Insulin Sensitivity in Chronic Kidney Disease

OBJECTIVE

In chronic kidney disease (CKD), dietary acid may promote metabolic acidosis and insulin resistance, which in turn may contribute to adverse clinical health outcomes. We examined associations between dietary acid load, serum bicarbonate, and insulin sensitivity in CKD.

DESIGN

In a cross-sectional study, we collected 3-day prospective food diaries to quantify dietary acid load as net endogenous acid production (NEAP, the nonvolatile acid load produced by the diet's acid balance) and potential renal acid load (PRAL). We measured urine net acid excretion (NAE) in 24-hour urine samples. Insulin sensitivity was measured by hyperinsulinemic euglycemic clamp.

SUBJECTS

Forty-two patients with CKD Stages 3 to 5 attending nephrology clinics in the Pacific Northwest and 21 control subjects (estimated glomerular filtration rate [eGFR] ≥ 60 mL/minute/1.73 m(2)).

MAIN OUTCOME MEASURES

Serum bicarbonate and insulin sensitivity (SIclamp).

RESULTS

Mean age was 60.8 ± 13.6 years, and 54% of participants were men. Mean eGFR and serum bicarbonate concentrations were 34.4 ± 13.1 mL/minute/1.73 m(2) and 24.1 ± 2.9 mEq/L for participants with CKD and 88.6 ± 14.5 mL/minute/1.73 m(2) and 26.3 ± 1.8 mEq/L for control subjects, respectively. Mean NEAP, PRAL, and NAE were 58.2 ± 24.3, 9.7 ± 18.4, and 32.1 ± 19.8 mEq/day, respectively. Considering all participants, dietary acid load was significantly, inversely associated with serum bicarbonate, adjusting for age, gender, race, eGFR, body mass index, and diuretic use: -1.2 mEq/L per standard deviation (SD) NEAP (95% confidence interval [CI] -1.8 to -0.6, P < .0001); -0.9 mEq/L bicarbonate per SD PRAL (95% CI -1.5 to -0.4, P = .0005); -0.7 mEq/L bicarbonate per SD NAE (95% CI -1.2 to -0.1, P = .01). These associations were similar in participants with and without CKD. However, neither NEAP and PRAL nor NAE was significantly associated with SIclamp. Serum bicarbonate was also not significantly associated with SIclamp.

CONCLUSIONS

In CKD, dietary acid load is associated with serum bicarbonate, suggesting that acidosis may be improved by dietary changes, but not with insulin sensitivity.

Metabolic Acidosis of CKD: An Update

The kidney has the principal role in the maintenance of acid-base balance. Therefore, a decrease in renal ammonium excretion and a positive acid balance often leading to a reduction in serum bicarbonate concentration are observed in the course of chronic kidney disease (CKD). The decrease in serum bicarbonate concentration is usually absent until glomerular filtration rate decreases to <20 to 25mL/min/1.73 m(2), although it can develop with lesser degrees of decreased kidney function. Non-anion gap acidosis, high-anion gap acidosis, or both can be found at all stages of CKD. The acidosis can be associated with muscle wasting, bone disease, hypoalbuminemia, inflammation, progression of CKD, and increased mortality. Administration of base may decrease muscle wasting, improve bone disease, and slow the progression of CKD. Base is suggested when serum bicarbonate concentration is <22 mEq/L, but the target serum bicarbonate concentration is unclear. Evidence that increments in serum bicarbonate concentration > 24 mEq/L might be associated with worsening of cardiovascular disease adds complexity to treatment decisions. Further study of the mechanisms through which metabolic acidosis contributes to the progression of CKD, as well as the pathways involved in mediating the benefits and complications of base therapy, is warranted.

A low-salt diet increases the estimated net endogenous acid production in nondiabetic chronic kidney disease patients treated with angiotensin receptor blockade

BACKGROUND/AIMS

An acid-base imbalance precedes renal disease progression in patients with chronic kidney disease (CKD). Little is known about the effects of a low-salt diet (LSD) on net endogenous acid production (NEAP) levels in CKD patients using angiotensin receptor blockade.

METHODS

We enrolled a total of 202 nondiabetic CKD patients who underwent an 8-week treatment with olmesartan from the original trial [Effects of Low Sodium Intake on the Antiproteinuric Efficacy of Olmesartan in Hypertensive Patients with Albuminuria (ESPECIAL) trial: NCT01552954]. The patients were divided into good- and poor-LSD-compliance groups.

RESULTS

During the interventional 8 weeks, the NEAP in the good-compliance group increased compared to the control group (12.9 ± 32.0 vs. -2.0 ± 35.0 mmol/day, p = 0.002). NEAP was positively associated with the good-LSD-compliance group in the fully adjusted analyses (r = 0.135, p = 0.016). The additional reduction of 2.39 g/day of protein intake with a reduction of 1 g/day of salt intake did not increase the NEAP under angiotensin II receptor blockade (ARB) treatment with an LSD (r = 0.546, p < 0.001).

CONCLUSION

We found that an LSD may increase the NEAP in nondiabetic CKD patients using ARB, which suggests that additional acid producing-protein restriction should be required to prevent the NEAP from rising.

Perceived barriers and facilitators of using dietary modification for CKD prevention among African Americans of low socioeconomic status: a qualitative study

Background

Factors influencing the use of dietary interventions for modification of CKD risk among African Americans have not been well-explored. We assessed perceived barriers and facilitators of CKD prevention through dietary modifications among African Americans with low socioeconomic status (SES) and at high risk for CKD.

Methods

We conducted a qualitative study involving three 90 minute focus groups of low SES (limited education, unemployed, uninsured, or income < $25,000/year) African American residents of Baltimore, Maryland (N = 17), who were aged 18-60 years, with no known history of CKD and (1) a family history of end stage renal disease and (2) self-reported diabetes, hypertension, cardiovascular disease, HIV or obesity. A trained moderator asked a series of 21 closed and open-ended questions. Group sessions were recorded, transcribed, and two independent investigators reviewed transcripts to identify common themes.

Results

Participants’ mean (SD) age was 39.8 (12.4) years. Most (59%) were female and earned < $5,000/year (71%). One quarter (24%) had self-reported diabetes and over half had hypertension (53%). Few (12%) perceived their CKD risk as high. Perceived barriers to CKD prevention through dietary change included the expense and unavailability of healthy foods, family member preferences, convenience of unhealthy foods, and inability to break lifelong habits. They identified vouchers for healthy foods, family-based interventions, nutritional counseling and group gatherings for persons interested in making dietary changes as acceptable facilitators of dietary CKD prevention efforts.

Conclusions

Low SES African Americans at high risk for CKD had limited perception of their risk but they identified multiple barriers and potential facilitators of CKD prevention via dietary modifications which can inform future studies and public health interventions.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2369-15-194) contains supplementary material, which is available to authorized users.

Dietary acid load and chronic kidney disease among adults in the United States

BACKGROUND

Diet can markedly affect acid-base status and it significantly influences chronic kidney disease (CKD) and its progression. The relationship of dietary acid load (DAL) and CKD has not been assessed on a population level. We examined the association of estimated net acid excretion (NAE(es)) with CKD; and socio-demographic and clinical correlates of NAE(es).

METHODS

Among 12,293 U.S. adult participants aged >20 years in the National Health and Nutrition Examination Survey 1999-2004, we assessed dietary acid by estimating NAE(es) from nutrient intake and body surface area; kidney damage by albuminuria; and kidney dysfunction by eGFR < 60 ml/min/1.73 m(2) using the MDRD equation. We tested the association of NAE(es) with participant characteristics using median regression; while for albuminuria, eGFR, and stages of CKD we used logistic regression.

RESULTS

Median regression results (β per quintile) indicated that adults aged 40-60 years (β [95% CI] = 3.1 [0.3-5.8]), poverty (β [95% CI] = 7.1 [4.01-10.22]), black race (β [95% CI] = 13.8 [10.8-16.8]), and male sex (β [95% CI] = 3.0 [0.7- 5.2]) were significantly associated with an increasing level of NAE(es). Higher levels of NAE(es) compared with lower levels were associated with greater odds of albuminuria (OR [95% CI] = 1.57 [1.20-2.05]). We observed a trend toward greater NAE(es) being associated with higher risk of low eGFR, which persisted after adjustment for confounders.

CONCLUSION

Higher NAE(es) is associated with albuminuria and low eGFR, and socio-demographic risk factors for CKD are associated with higher levels of NAE(es). DAL may be an important target for future interventions in populations at high risk for CKD.