New perspectives on acid-base balance

The association of dietary acid load (DAL) with estimated skeletal muscle mass and bone mineral content: a cross-sectional study

BACKGROUND & AIMS

Dietary patterns that promote mild metabolic acidosis may have a negative effect on bone and muscle, and a high dietary acid load (DAL) may be detrimental to skeletal muscle mass and bone mineral content. However, the association between skeletal muscle mass and bone mineral content with dietary acid load has not been consistently reported in previous studies. The objective of the study was to evaluate the association of potential renal net acid load (PRAL) and net endogenous acid production (NEAP) with bone mineral content and skeletal muscle mass in pre-menopause women with overweight or obesity in Iran.

METHOD

Three hundred and ninety women with a body mass index (BMI) of 25 were included in this cross-sectional study. We used a validated 147-item semi-quantitative food frequency questionnaire (FFQ) for evaluating the dietary intake. Based on the dietary data, potential renal net acid load (PRAL) and net endogenous acid production (NEAP) were calculated. Muscle mass and bone mineral content were estimated by a bioelectrical impedance analyzer (BIA).

RESULTS

After controlling for potential confounders, we discovered a significant linear relationship between PRAL (β = -0.027, 95%CI = -0.049 to -0.004, P = 0.02) and NEAP (β = -0.05, 95%CI = -0.097 to -0.003, P = 0.03) and skeletal muscle mass index. However, there was no significant difference between SMM and BMC across PRAL and NEAP tertiles.

CONCLUSION

PRAL and NEAP were found to be inversely related to skeletal muscle mass index among overweight/obese women. Further research is required to establish whether this relationship is important for musculoskeletal health in these populations.

Effect of Bicarbonate on Net Acid Excretion, Blood Pressure, and Metabolism in Patients With and Without CKD: The Acid Base Compensation in CKD Study

RATIONALE & OBJECTIVE

Patients with CKD are at elevated risk of metabolic acidosis due to impaired net acid excretion (NAE). Identifying early markers of acidosis may guide prevention in chronic kidney disease (CKD). This study compared NAE in participants with and without CKD, as well as the NAE, blood pressure (BP), and metabolomic response to bicarbonate supplementation.

STUDY DESIGN

Randomized order, cross-over study with controlled feeding.

SETTING & PARTICIPANTS

Participants consisted of 8 patients with CKD (estimated glomerular filtration rate 30-59mL/min/1.73m² or 60-70mL/min/1.73m² with albuminuria) and 6 patients without CKD. All participants had baseline serum bicarbonate concentrations between 20 and 28 mEq/L; they did not have diabetes mellitus and did not use alkali supplements at baseline.

INTERVENTION

Participants were fed a fixed-acid-load diet with bicarbonate supplementation (7 days) and with sodium chloride control (7 days) in a randomized order, cross-over fashion.

OUTCOMES

Urine NAE, 24-hour ambulatory BP, and 24-hour urine and plasma metabolomic profiles were measured after each period.

RESULTS

During the control period, mean NAE was 28.3±10.2 mEq/d overall without differences across groups (P=0.5). Urine pH, ammonium, and citrate were significantly lower in CKD than in non-CKD (P<0.05 for each). Bicarbonate supplementation reduced NAE and urine ammonium in the CKD group, increased urine pH in both groups (but more in patients with CKD than in those without), and increased; urine citrate in the CKD group (P< 0.2 for interaction for each). Metabolomic analysis revealed several urine organic anions were increased with bicarbonate in CKD, including 3-indoleacetate, citrate/isocitrate, and glutarate. BP was not significantly changed.

LIMITATIONS

Small sample size and short feeding duration.

CONCLUSIONS

Compared to patients without CKD, those with CKD had lower acid excretion in the form of ammonium but also lower base excretion such as citrate and other organic anions, a potential compensation to preserve acid-base homeostasis. In CKD, acid excretion decreased further, but base excretion (eg, citrate) increased in response to alkali. Urine citrate should be evaluated as an early and responsive marker of impaired acid-base homeostasis.

FUNDING

National Institute of Diabetes and Digestive and Kidney Diseases and the Duke O'Brien Center for Kidney Research.

TRIAL REGISTRATION

Registered at ClinicalTrials.gov with study number NCT02427594.

Oral Sodium Bicarbonate Supplementation Does Not Affect Serum Calcification Propensity in Patients with Chronic Kidney Disease and Chronic Metabolic Acidosis

BACKGROUND

Cardiovascular disease is the leading cause of death in patients with chronic kidney disease (CKD) and metabolic acidosis might accelerate vascular calcification. The T50 calcification inhibition test (T50-test) is a global functional test analyzing the overall propensity of calcification in serum, and low T50-time is associated with progressive aortic stiffening and with all-cause mortality in non-dialysis CKD, dialysis, and transplant patients. Low serum bicarbonate is associated with a short T50-time and alkali supplementation could be a simple modifier of calcification propensity. The aim of this study was to investigate the short-term effect of oral sodium bicarbonate supplementation on T50-time in CKD patients.

MATERIAL AND METHODS

The SoBic-study is an ongoing randomized-controlled trial in CKD-G3 and G4 patients with chronic metabolic acidosis (serum HCO3- ≤21 mmol/L), in which patients are randomized to either achieve serum HCO3- levels of 24 ± 1 mmol/L (intervention group) or 20 ± 1 mmol/L (rescue group). The effect of bicarbonate treatment on T50-time was assessed.

RESULTS

The study cohort consisted of 35 (14 female) patients aged 57 (±15) years, and 18 were randomized to the intervention group. The mean T50-time was 275 (± 64) min. After 4 weeks, the mean change of T50-time was 4 (±69) min in the intervention group and 18 min (±56) in the rescue group (β = -25; 95% CI: -71 to 22; p = 0.298). Moreover, change of serum bicarbonate in individual patients was not associated with change in T50-time, analyzed by regression analysis. Change of serum phosphate had a significant impact on change of T50-time (β = -145; 95% CI: -237 to -52).

CONCLUSION

Oral sodium bicarbonate supplementation showed no effect on T50-time in acidotic CKD patients.

Acid Balance, Dietary Acid Load, and Bone Effects-A Controversial Subject

Modern Western diets, with higher contents of animal compared to fruits and vegetable products, have a greater content of acid precursors vs. base precursors, which results in a net acid load to the body. To prevent inexorable accumulation of acid in the body and progressively increasing degrees of metabolic acidosis, the body has multiple systems to buffer and titrate acid, including bone which contains large quantities of alkaline salts of calcium. Both in vitro and in vivo studies in animals and humans suggest that bone base helps neutralize part of the dietary net acid load. This raises the question of whether decades of eating a high acid diet might contribute to the loss of bone mass in osteoporosis. If this idea is true, then additional alkali ingestion in the form of net base-producing foods or alkalinizing salts could potentially prevent this acid-related loss of bone. Presently, data exists that support both the proponents as well as the opponents of this hypothesis. Recent literature reviews have tended to support either one side or the other. Assuming that the data cited by both sides is correct, we suggest a way to reconcile the discordant findings. This overview will first discuss dietary acids and bases and the idea of changes in acid balance with increasing age, then review the evidence for and against the usefulness of alkali therapy as a treatment for osteoporosis, and finally suggest a way of reconciling these two opposing points of view.

Effect of cation-anion balance in feed on urine pH in rabbits in comparison with other species

In the present investigation, the impact of diet composition on urine pH in rabbits was compared with previous studies on rabbits, cats, dogs, pigs and horses. A total of 13 dwarf rabbits were fed six different diets with a cation-anion balance (CAB) between -39 and +320 mmol/kg dry matter (DM) using ammonium chloride (NH₄ Cl) as an acidifier. CAB was calculated as follows: CAB (mmol/kg DM) = 49.9*Ca + 82.3*Mg +43.5*Na + 25.6*K - 59*P - 62.4*S - 28.2*Cl; minerals in g/kg DM. Urine, faeces and blood were collected. Urine pH ranged from 5.26 ± 0.22 at a CAB of -39 mmol/kg DM to 8.56 ± 0.24 at a CAB of +320 mmol/kg DM. A low CAB in the feed reduced blood pH and blood base excess significantly. Renal excretion of Ca, P, Na and Mg and water was significantly higher in rabbits eating acidifying diets. In comparison with other species, rabbits reacted to acidifying diets in a similar way as cats, dogs and pigs. Rabbits on a mildly alkalizing diet, however, had a trend to higher urine pH than other monogastric species on such diets (cats, dogs, pigs, horses).

Draining and salting as responsible key steps in the generation of the acid-forming potential of cheese: Application to a soft blue-veined cheese

A disregarded nutritional feature of cheeses is their high acid-forming potential when ingested, which is associated with deleterious effects on consumers' health. This work aimed to characterize the acid-forming potential of a blue-veined cheese during manufacturing to identify the main steps of the process involved in this phenomenon. Sampling was performed on 3 batches at 10 steps of the cheese-making process: reception of raw milk, pasteurization, maturation of milk, coagulation, stirring, draining of the curds, and 4 ripening stages: 21, 28, 42, and 56d. The acid-forming potential of each sample was evaluated by (1) the calculation of the potential renal acid load (PRAL) index (considering protein, Cl, P, Na, K, Mg, and Ca contents), and (2) its organic anion content (lactate and citrate), considered as alkalinizing elements. Draining and salting were identified as the main steps responsible for generation of the acid-forming potential of cheese. The draining process induced an increase in the PRAL index from 1.2mEq/100g in milk to 10.4mEq/100g in drained curds due to the increase in dry matter and the loss of alkaline minerals into the whey. The increase in PRAL value (20.3mEq/100g at d 56) following salting resulted from an imbalance between the strong acidogenic elements (Cl, P, and proteins) and the main alkalinizing ones (Na and Ca). Particularly, Cl had a major effect on the PRAL value. Regarding organic anions, draining induced a loss of 93% of the citrate content in initial milk. The lactate content increased as fermentation occurred (1,297.9mg/100g in drained curds), and then decreased during ripening (519.3mg/100g at d 56). This lactate level probably helps moderate the acidifying potential of end products. Technological strategies aimed at limiting the acid-forming potential of cheeses are proposed and deserve further research to evaluate their nutritional relevance.

The acid-ash hypothesis revisited: a reassessment of the impact of dietary acidity on bone

The acid-ash hypothesis states that when there are excess blood protons, bone is eroded to provide alkali to buffer the net acidity and maintain physiologic pH. There is concern that with the typical Western diet, we are permanently in a state of net endogenous acid production, which is gradually reducing bone. While it is clear that a high acid-producing diet generates increased urinary acid and calcium excretion, the effect of diet does not always have the expected results on BMD, fracture risk and markers of bone formation and resorption, suggesting that other factors are influencing the effect of acid/alkali loading on bone. High dietary protein, sodium and phosphorus intake, all of which are necessary for bone formation, were thought to be net acid forming and contribute to low BMD and fracture risk, but appear under certain conditions to be beneficial, with the effect of protein being driven by calcium repletion. Dietary salt can increase short-term markers of bone resorption but may also trigger 1,25(OH)2D synthesis to increase calcium absorption; with low calcium intake, salt intake may be inversely correlated with BMD but with high calcium intake, salt intake was positively correlated with BMD. With respect to the effect of phosphorus, the data are conflicting. Inclusion of an analysis of calcium intake may help to reconcile the contradictory results seen in many of the studies of bone. The acid-ash hypothesis could, therefore, be amended to state that with an acid-producing diet and low calcium intake, bone is eroded to provide alkali to buffer excess protons but where calcium intake is high the acid-producing diet may be protective.

Nutritional disturbance in acid-base balance and osteoporosis: a hypothesis that disregards the essential homeostatic role of the kidney

The nutritional acid load hypothesis of osteoporosis is reviewed from its historical origin to most recent studies with particular attention to the essential but overlooked role of the kidney in acid–base homeostasis. This hypothesis posits that foods associated with an increased urinary acid excretion are deleterious for the skeleton, leading to osteoporosis and enhanced fragility fracture risk. Conversely, foods generating neutral or alkaline urine would favour bone growth and Ca balance, prevent bone loss and reduce osteoporotic fracture risk. This theory currently influences nutrition research, dietary recommendations and the marketing of alkaline salt products or medications meant to optimise bone health and prevent osteoporosis. It stemmed from classic investigations in patients suffering from chronic kidney diseases (CKD) conducted in the 1960s. Accordingly, in CKD, bone mineral mobilisation would serve as a buffer system to acid accumulation. This interpretation was later questioned on both theoretical and experimental grounds. Notwithstanding this questionable role of bone mineral in systemic acid–base equilibrium, not only in CKD but even more in the absence of renal impairment, it is postulated that, in healthy individuals, foods, particularly those containing animal protein, would induce ‘latent’ acidosis and result, in the long run, in osteoporosis. Thus, a questionable interpretation of data from patients with CKD and the subsequent extrapolation to healthy subjects converted a hypothesis into nutritional recommendations for the prevention of osteoporosis. In a historical perspective, the present review dissects out speculation from experimental facts and emphasises the essential role of the renal tubule in systemic acid–base and Ca homeostasis.

Systemic acid load from the diet affects maximal-exercise RER

A maximal-exercise RER (RER(max) ≥ 1.10 is commonly used as a criterion to determine whether a "true" maximal oxygen uptake (V˙O(2max)) has been attained during maximal-effort exercise testing. Because RER(max) is heavily influenced by CO2 production from acid buffering during maximal exercise, we postulated that dietary acid load, which affects acid-base regulation, might contribute to variability in RER(max).

PURPOSE

The study's purpose was to determine whether a habitual dietary intake that promotes systemic alkalinity results in higher RER(max) during V˙O(2max) testing.

METHODS

Sedentary men and women (47-63 yr, n = 57) with no evidence of cardiovascular disease underwent maximal graded treadmill exercise tests. V˙O(2max) and RER(max) were measured with indirect calorimetry. Habitual diet was assessed for its long-term effect on systemic acid-base status by performing nutrient analysis of food diaries and using this information to calculate the potential renal acid load (PRAL). Participants were grouped into tertiles on the basis of PRAL.

RESULTS

The lowest PRAL tertile (alkaline PRAL) had higher RERmax values (1.21 ± 0.01, P ≤ 0.05) than the middle PRAL tertile (1.17 ± 0.01) and highest PRAL tertile (1.15 ± 0.01). There were no significant differences (all P ≥ 0.30) among PRAL tertiles for RER at submaximal exercise intensities of 70%, 80%, or 90% V˙O2max. After controlling for age, sex, V˙O(2max), and HRmax, regression analysis demonstrated that 19% of the variability in RER(max) was attributed to PRAL (r = -0.43, P = 0.001). Unexpectedly, HRmax was lower (P ≤ 0.05) in the low PRAL tertile (164 ± 3 beats·min⁻¹) versus the highest PRAL tertile (173 ± 3 beats·min⁻¹).

CONCLUSIONS

These results suggest that individuals on a diet that promotes systemic alkalinity may more easily achieve the RER(max) criterion of ≥ 1.10, which might lead to false-positive conclusions about achieving maximal effort and V˙O(2max) during graded exercise testing.

Impact of the diet on net endogenous acid production and acid-base balance

Net acid production, which is composed of volatile acids (15,000 mEq/day) and metabolic acids (70-100 mEq/day) is relatively small compared to whole-body H⁺ turnover (150,000 mEq/day). Metabolic acids are ingested from the diet or produced as intermediary or end products of endogenous metabolism. The three commonly reported sources of net acid production are the metabolism of sulphur amino acids, the metabolism or ingestion of organic acids, and the metabolism of phosphate esters or dietary phosphoproteins. Net base production occurs mainly as a result of absorption of organic anions from the diet. To maintain acid-base balance, ingested and endogenously produced acids are neutralized within the body by buffer systems or eliminated from the body through the respiratory (excretion of volatile acid in the form of CO₂) and urinary (excretion of fixed acids and remaining H⁺) pathways. Because of the many reactions involved in the acid-base balance, the direct determination of acid production is complex and is usually estimated through direct or indirect measurements of acid excretion. However, indirect approaches, which assess the acid-forming potential of the ingested diet based on its composition, do not take all the acid-producing reactions into account. Direct measurements therefore seem more reliable. Nevertheless, acid excretion does not truly provide information on the way acidity is dealt with in the plasma and this measurement should be interpreted with caution when assessing acid-base imbalance.

Causal assessment of dietary acid load and bone disease: a systematic review & meta-analysis applying Hill's epidemiologic criteria for causality

Background

Modern diets have been suggested to increase systemic acid load and net acid excretion. In response, alkaline diets and products are marketed to avoid or counteract this acid, help the body regulate its pH to prevent and cure disease. The objective of this systematic review was to evaluate causal relationships between dietary acid load and osteoporosis using Hill's criteria.

Methods

Systematic review and meta-analysis. We systematically searched published literature for randomized intervention trials, prospective cohort studies, and meta-analyses of the acid-ash or acid-base diet hypothesis with bone-related outcomes, in which the diet acid load was altered, or an alkaline diet or alkaline salts were provided, to healthy human adults. Cellular mechanism studies were also systematically examined.

Results

Fifty-five of 238 studies met the inclusion criteria: 22 randomized interventions, 2 meta-analyses, and 11 prospective observational studies of bone health outcomes including: urine calcium excretion, calcium balance or retention, changes of bone mineral density, or fractures, among healthy adults in which acid and/or alkaline intakes were manipulated or observed through foods or supplements; and 19 in vitro cell studies which examined the hypothesized mechanism. Urine calcium excretion rates were consistent with osteoporosis development; however calcium balance studies did not demonstrate loss of whole body calcium with higher net acid excretion. Several weaknesses regarding the acid-ash hypothesis were uncovered: No intervention studies provided direct evidence of osteoporosis progression (fragility fractures, or bone strength as measured using biopsy). The supporting prospective cohort studies were not controlled regarding important osteoporosis risk factors including: weight loss during follow-up, family history of osteoporosis, baseline bone mineral density, and estrogen status. No study revealed a biologic mechanism functioning at physiological pH. Finally, randomized studies did not provide evidence for an adverse role of phosphate, milk, and grain foods in osteoporosis.

Conclusions

A causal association between dietary acid load and osteoporotic bone disease is not supported by evidence and there is no evidence that an alkaline diet is protective of bone health.

Low urine pH and acid excretion do not predict bone fractures or the loss of bone mineral density: a prospective cohort study

Background

The acid-ash hypothesis, the alkaline diet, and related products are marketed to the general public. Websites, lay literature, and direct mail marketing encourage people to measure their urine pH to assess their health status and their risk of osteoporosis.

The objectives of this study were to determine whether 1) low urine pH, or 2) acid excretion in urine [sulfate + chloride + 1.8x phosphate + organic acids] minus [sodium + potassium + 2x calcium + 2x magnesium mEq] in fasting morning urine predict: a) fragility fractures; and b) five-year change of bone mineral density (BMD) in adults.

Methods

Design: Cohort study: the prospective population-based Canadian Multicentre Osteoporosis Study. Multiple logistic regression was used to examine associations between acid excretion (urine pH and urine acid excretion) in fasting morning with the incidence of fractures (6804 person years). Multiple linear regression was used to examine associations between acid excretion with changes in BMD over 5-years at three sites: lumbar spine, femoral neck, and total hip (n = 651). Potential confounders controlled included: age, gender, family history of osteoporosis, physical activity, smoking, calcium intake, vitamin D status, estrogen status, medications, renal function, urine creatinine, body mass index, and change of body mass index.

Results

There were no associations between either urine pH or acid excretion and either the incidence of fractures or change of BMD after adjustment for confounders.

Conclusion

Urine pH and urine acid excretion do not predict osteoporosis risk.

Meta-analysis of the quantity of calcium excretion associated with the net acid excretion of the modern diet under the acid-ash diet hypothesis

BACKGROUND

The acid-ash diet hypothesis of osteoporosis suggests that acid from the modern diet causes a demineralization of the skeleton, and mobilized bone calcium is excreted. A systematic approach has not been used to summarize the findings of the numerous studies about the hypothesis.

OBJECTIVES

The purpose of this meta-analysis was to estimate the quantity of net acid excretion and calciuria associated with the modern diet, to assess the association between acid excretion and calcium excretion, and to assess the influence of urine preservatives on calcium measurement.

DESIGN

We systematically searched for trials of the acid-ash hypothesis and conducted a meta-analysis.

RESULTS

Twenty-five of 105 studies met the inclusion criteria. The estimated quantity of net acid excretion from the weighted average of the control diets from 11 studies was 47 mEq/d. The increase in urinary calcium with a change in renal net acid excretion depended on whether the urine was acidic or alkaline (P < 0.001). A significant linear relation was observed between net acid excretion and calcium excretion for both acidic and alkaline urine (P < 0.001). The estimated change in urine calcium associated with a change of 47 mEq of net acid excretion in acidic urine was 1.6 mmol/d (66 mg/d) of calcium.

CONCLUSION

Evidence suggests a linear association between changes in calcium excretion in response to experimental changes in net acid excretion. However, this finding is not evidence that the source of the excreted calcium is bone or that this calciuria contributes to the development of osteoporosis.

Bone mineral status and its relation with dietary estimates of net endogenous acid production in Hong Kong Chinese adolescents

Diet composition influences net endogenous acid production (NEAP), which may affect bone health. No studies are available to relate dietary estimate of NEAP to bone health in Chinese adolescents. This study examined the association of dietary estimates of NEAP with bone mineral status in Hong Kong Chinese adolescents. Baseline data on 171 boys and 180 girls aged 10-12 years from the Hong Kong Adolescent Bone Health Cohort Study were presented. Weight, height, Tanner stage and dietary intakes by FFQ were collected. NEAP was estimated from diet using Frassetto's method. Bone area (BA), bone mineral content (BMC) and bone mineral apparent density (BMAD) of total hip, lumbar (L1-L4) spine and whole body were estimated by dual-energy X-ray absorptiometry (DXA). No significant association was observed between BMC or BMAD and energy-adjusted NEAP or other nutrients. BA was significantly and positively associated with BMC at all sites in both sexes. Weight was significantly and positively associated with BMC in hip and spine in both sexes. Height was negatively correlated with hip BMC for boys and whole body BMC for girls. Pubertal stage was significantly and positively associated with BMC in all sites in both sexes. Weight and height contributed most of the variability in BMAD at different sites. The results suggest that anthropometric characteristics and pubertal stage are more influential than dietary NEAP in determining bone mineral status of Hong Kong Chinese adolescents. However, the methodological weaknesses regarding the use of DXA and FFQ in the present sample require attention.

Organic anions and potassium salts in nutrition and metabolism

The present review examines the importance of dietary organic anions in preventive nutrition. Organic anions are chiefly supplied by plant foods, as partially neutralised K salts such as potassium citrate, potassium malate and, to a lesser extent, oxalate or tartrate salts. Animal products may also supply K anions, essentially as phosphate, but also as lactate as a result of fermentative or maturation processes, but these K salts have little alkalinising significance. Citrate and malate anions are absorbed in the upper digestive tract, while a substantial proportion is probably metabolised in the splanchnic area. Whatever their site of metabolism, these anions finally yield KHCO3which is used by the kidneys to neutralise fixed acidity. This acidity essentially reflects the oxidation of excess S amino acids to sulfate ions, which is mainly related to the dietary protein level. Failure to neutralise acidity leads to low-grade metabolic acidosis, with possible long-term deleterious effects on bone Ca status and on protein status. Furthermore, low-grade acidosis is liable to affect other metabolic processes, such as peroxidation of biological structures. These metabolic disturbances could be connected with the relatively high incidence of osteoporosis and muscle-protein wasting problems observed in ageing individuals in Europe and Northern America. Providing a sufficient supply of K organic anions through fruit and vegetable intake should be recommended, fostering the actual motivational campaigns ('five (or ten) per d') already launched to promote the intake of plant foods rich in complex carbohydrates and various micronutrients.

Posttransplant metabolic acidosis: a neglected factor in renal transplantation?

PURPOSE OF REVIEW

The occurrence and pathogenesis of metabolic acidosis after renal transplantation is reviewed. Posttransplant acidosis is shown to be a key mechanism for major metabolic complications in mineral and muscle metabolism, and for anemia, discussed in the context of both acidosis and renal transplantation.

RECENT FINDINGS

Continuous improvement in kidney transplant survival has shifted attention to long-term outcomes, specifically to disorders linked to cardiovascular disease, physical capacity and quality of life. Metabolic acidosis is gaining growing acceptance as a clinical entity and has occasionally come into focus in the context of renal transplantation. The possible link to metabolic disturbances resulting in impairment of musculoskeletal disorders and physical limitations, however, has not been considered specifically.

SUMMARY

Available evidence suggests a high prevalence of (compensated) metabolic acidosis after renal transplantation, presenting as low serum bicarbonate and impaired renal acid excretion. This condition is associated with relevant disorders in mineral metabolism and muscle function. Current knowledge about the effects of acidosis on renal electrolyte handling, mineral metabolism and protein synthesis suggests that acid/base derangements contribute to the muscle and bone pathology, as well as anemia, encountered after kidney transplantation. Consequently, posttransplant acidosis may be a relevant factor in the causal pathway of impaired physical capacity observed in this patient group.

Plasma acid-base changes in chronic renal failure: a Stewart analysis

The bicarbonate centered approach to acid-base physiology involves complex explanations for the metabolic acidosis associated with chronic renal failure. We used the alternate Stewart approach to acid-base physiology to quantify the acid-base chemistry of patients with chronic renal failure. We examined the plasma and urine chemistry of 19 patients with chronic renal failure who were predialysis and 20 healthy volunteers. We compared the plasma strong-ion-difference due to sodium,potassium,and chloride ions as well as the weak acids albumin and phosphate. We used a simplified Fencl-Stewart approach to quantify the effects of sodium-chloride, albumin, and unmeasured ions on base-excess. The chronic renal failure group had a greater metabolic acidosis, with a base-excess that differed from the healthy group by a mean of -2.7 mmol/L, p = 0.04. This was associated with a strong ion acidosis due to both increased chloride and decreased sodium. The anion gap, strong-ion-gap, and base-excess effect of unmeasured ions were similar in both groups suggesting that unmeasured ions had only a minor role in the acid-base status in this group of patients.

Metabolic acidosis in maintenance dialysis patients: clinical considerations

Metabolic acidosis in maintenance dialysis patients: Clinical considerations. Metabolic acidosis is a common consequence of advanced chronic renal failure (CRF) and maintenance dialysis (MD) therapies are not infrequently unable to completely correct the base deficit. In MD patients, severe metabolic acidosis is associated with an increased relative risk for death. The chronic metabolic acidosis of the severity commonly encountered in patients with advanced CRF has two well-recognized major systemic consequences. First, metabolic acidosis induces net negative nitrogen and total body protein balance, which improves upon bicarbonate supplementation. The data suggest that metabolic acidosis is both catabolic and antianabolic. Emerging data also indicate that metabolic acidosis may be one of the triggers for chronic inflammation, which may in turn promote protein catabolism among MD patients. In contrast to these findings, metabolic acidosis may be associated with a decrease in hyperleptinemia associated with CRF. Several studies have shown that correction of metabolic acidosis among MD patients is associated with modest improvements in the nutritional status. Second, metabolic acidosis has several effects on bone, causing physicochemical dissolution of bone and cell-mediated bone resorption (inhibition of osteoblast and stimulation of osteoclast function). Metabolic acidosis is probably also associated with worsening of secondary hyperparathyroidism. Data on the effect of correction of metabolic acidosis on renal osteodystrophy, however, are limited. Preliminary evidence suggest that metabolic acidosis may play a role in beta2-microglobulin accumulation, as well as the hypertriglyceridemia seen in renal failure. Given the body of evidence pointing to the several systemic consequences of metabolic acidosis, a more aggressive approach to the correction of metabolic acidosis is proposed.

Dietary protein and bone health

The effects of dietary protein on bone health are paradoxical and need to be considered in context of the age, health status and usual diet of the population. Over the last 80 years numerous studies have demonstrated that a high protein intake increases urinary Ca excretion and that on average 1 mg Ca is lost in urine for every 1 g rise in dietary protein. This relationship is primarily attributable to metabolism of S amino acids present in animal and some vegetable proteins, resulting in a greater acid load and buffering response by the skeleton. However, many of these early studies that demonstrated the calciuric effects of protein were limited by low subject numbers, methodological errors and the use of high doses of purified forms of protein. Furthermore, the cross-cultural and population studies that showed a positive association between animal-protein intake and hip fracture risk did not consider other lifestyle or dietary factors that may protect or increase the risk of fracture. The effects of protein on bone appear to be biphasic and may also depend on intake of Ca- and alkali-rich foods, such as fruit and vegetables. At low protein intakes insulin-like growth factor production is reduced, which in turn has a negative effect on Ca and phosphate metabolism, bone formation and muscle cell synthesis. Although growth and skeletal development is impaired at very low protein intakes, it is not known whether variations in protein quality affect the achievement of optimal peak bone mass in adolescents and young adults. Prospective studies in the elderly in the USA have shown that the greatest bone losses occur in elderly men and women with an average protein intake of 16-50 g/d. Although a low protein intake may be indicative of a generally poorer diet and state of health, there is a need to evaluate whether there is a lower threshold for protein intake in the elderly in Europe that may result in increased bone loss and risk of osteoporotic fracture.

Toxicity and carcinogenicity of acidogenic or alkalogenic diets in rats; effects of feeding NH 4 Cl, KHCO 3 or KCl

The effects of diet-induced acid-base disturbances were examined in 4-week, 13-week and 18-month toxicity studies, and in a 30-month carcinogenicity study. Rats were fed a natural ingredient diet (controls), supplemented with 2% or 4% KHCO(3) (base-forming diets), or with 1% or 2.1% NH(4)Cl (acid-forming diets). Additional controls were fed 3% KCl (neutral diet providing K(+) and Cl(-) in amounts equimolar to those in the 4% KHCO(3) diet and the 2.1% NH(4)Cl diet, respectively). NH(4)Cl induced the expected metabolic acidosis, as shown by decreased base excess in blood, decreased urinary pH and increased urinary net acid excretion. KHCO(3) induced the opposite effects. KCl did not affect the acid-base balance. Clinical condition and death rate were not affected. The feeding of high levels of each salt resulted in growth retardation and increased water intake and urinary volume. Plasma potassium and urinary potassium excretion were increased with KHCO(3) and KCl. Plasma chloride was increased with NH(4)Cl, but not with KCl. Urinary calcium and phosphate excretion were increased with NH(4)Cl, but there were no indications that bone minerals were involved (weight, calcium content and fat free solid of the femur were not affected). Standard haematological and clinical chemistry parameters were not affected. Kidney weights were increased with 2.1% NH(4)Cl. Hypertrophy of the adrenal zona glomerulosa occurred with KHCO(3), KCl and NH(4)Cl, due to chronic stimulation of the adrenal cortex by either K(+) or by NH(4)Cl-induced acidosis. An early onset (from week 13) of oncocytic tubules was noted in the kidneys of rats fed KHCO(3) and, after 30 months, the incidence of this lesion was much higher than the background incidence in ageing controls. No progression to oncocytomas was noted. KCl showed only slight effects on the early onset of oncocytic tubules (from 18 months). In contrast, the severity of nephrosis and the incidence of oncocytic tubules were decreased with 2.1% NH(4)Cl, suggesting a protective effect of acidosis. The feeding of KHCO(3) resulted in hyperplasia, papillomas and carcinomas of the urinary bladder. With KCl only a slight increase in proliferative urothelial lesions was noted. Apart from these (pre-)neoplastic lesions in the urinary bladder there were no treatment-related differences in tumour response among the groups. We concluded that most of the observed changes represent physiological adaptations to the feeding of acid- or base-forming salts. Remarkable effects noted with KHCO(3), and to a far lesser extent with KCl, consisted of renal oncocytic tubules and (pre-)neoplastic lesions of the urinary bladder epithelium. NH(4)Cl-induced chronic metabolic acidosis was not associated with dissolution of alkaline bone salts in rats. Finally, a protective effect of chronic acidosis on tumour development was not found.

UK Food Standards Agency alpha-linolenic acid workshop report

The UK Food Standards Agency convened a group of expert scientists to review current research investigating whether n-3 polyunsaturated fatty acids (PUFA) from plant oils (alpha-linolenic acid; ALA) were as beneficial to cardiovascular health as the n-3 PUFA from the marine oils, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The workshop also aimed to establish priorities for future research. Dietary intake of ALA has been associated with a beneficial effect on CHD; however, the results from studies investigating the effects of ALA supplementation on CHD risk factors have proved equivocal. The studies presented as part of the present workshop suggested little, if any, benefit of ALA, relative to linoleic acid, on risk factors for cardiovascular disease; the effects observed with fish-oil supplementation were not replicated by ALA supplementation. There is a need, therefore, to first prove the efficacy of ALA supplementation on cardiovascular disease, before further investigating effects on cardiovascular risk factors. The workshop considered that a beneficial effect of ALA on the secondary prevention of CHD still needed to be established, and there was no reason to look further at existing CHD risk factors in relation to ALA supplementation. The workshop also highlighted the possibility of feeding livestock ALA-rich oils to provide a means of increasing the dietary intake in human consumers of EPA and DHA.