Excessive dietary phosphorus intake impairs endothelial function in young healthy men: a time- and dose-dependent study

Effect of a plant protein-rich diet on postprandial phosphate metabolism in healthy adult men: a randomised controlled trial

BACKGROUND

This study examined the effects of animal protein- and plant protein-rich diets on postprandial phosphorus metabolism in healthy male subjects.

METHODS

The study was conducted by randomised parallel-group comparison of healthy men aged 21-24 years. In Study 1, participants were divided into two groups and consumed either a 70% animal protein diet (AD, n = 6) or a 70% plant protein diet (PD, n = 6). In Study 2, participants were divided into three groups and consumed either AD (n = 10), PD (n = 10) or AD + DF, a 70% animal protein diet loaded with the same amount of fibre as PD (n = 9). The phosphorus contents of the diets used in this study were nearly equivalent (AD, 710.1 mg; PD, 709.7 mg; AD + DF, 708.9 mg). Blood and urine samples were collected before, and 2 and 4 h after the meal to measure phosphorus and calcium levels.

RESULTS

In Study 1, PD consumption resulted in lower blood and urinary phosphorus concentrations 2 h postprandially compared with AD (p < 0.05). In Study 2, blood phosphorus levels in AD + DF after the diet remained lower, but not significantly so compared with AD, and urinary phosphorus levels were significantly lower 2 h postprandially (p < 0.05).

CONCLUSIONS

A plant protein-rich diet reduced rapid postprandial increases in blood and urinary phosphorus concentrations compared with the animal protein-rich diets, suggesting that dietary fibre may play a partial role in the postprandial decreases in blood and urinary phosphorus concentrations.

Phosphate in Cardiovascular Disease: From New Insights Into Molecular Mechanisms to Clinical Implications

Hyperphosphatemia is a common feature in patients with impaired kidney function and is associated with increased risk of cardiovascular disease. This phenomenon extends to the general population, whereby elevations of serum phosphate within the normal range increase risk; however, the mechanism by which this occurs is multifaceted, and many aspects are poorly understood. Less than 1% of total body phosphate is found in the circulation and extracellular space, and its regulation involves multiple organ cross talk and hormones to coordinate absorption from the small intestine and excretion by the kidneys. For phosphate to be regulated, it must be sensed. While mostly enigmatic, various phosphate sensors have been elucidated in recent years. Phosphate in the circulation can be buffered, either through regulated exchange between extracellular and cellular spaces or through chelation by circulating proteins (ie, fetuin-A) to form calciprotein particles, which in themselves serve a function for bulk mineral transport and signaling. Either through direct signaling or through mediators like hormones, calciprotein particles, or calcifying extracellular vesicles, phosphate can induce various cardiovascular disease pathologies: most notably, ectopic cardiovascular calcification but also left ventricular hypertrophy, as well as bone and kidney diseases, which then propagate phosphate dysregulation further. Therapies targeting phosphate have mostly focused on intestinal binding, of which appreciation and understanding of paracellular transport has greatly advanced the field. However, pharmacotherapies that target cardiovascular consequences of phosphate directly, such as vascular calcification, are still an area of great unmet medical need.

Can we reverse arterial stiffness by intervening on CKD-MBD biomarkers?

The increased cardiovascular risk of chronic kidney disease may in part be the consequence of arterial stiffness, a typical feature of kidney failure. Deranged homeostasis of minerals and hormones involved (CKD-MBD), are also strongly associated with this increased risk. It is well established that CKD-MBD is a main driver of vascular calcification, which in turn worsens arterial stiffness. However, there are other contributors to arterial stiffness in CKD than calcification. An overlooked possibility is that CKD-MBD may have detrimental effects on this potentially better modifiable component of arterial stiffness. In this review, the individual contributions of short-term changes in calcium, phosphate, PTH, vitamin D, magnesium, and FGF23 to arterial stiffness, in most studies assessed as pulse wave velocity, is summarized. Indeed, there is evidence from both observational studies and interventional trials that higher calcium concentrations can worsen arterial stiffness. This, however, has not been shown for phosphate, and it seems unlikely that, apart from being a contributor to vascular calcification and having effects on the microcirculation, phosphate has no acute effect on large artery stiffness. Several interventional studies, both by infusing PTH and by abrupt lowering PTH by calcimimetics or surgery, virtually ruled out direct effects on large artery stiffness. A well-designed trial using both active and nutritional vitamin D as intervention found a beneficial effect for the latter. Unfortunately, the study had a baseline imbalance and other studies did not support its finding. Both magnesium and FGF23 do not seem do modify central arterial stiffness.

The effect of dietary phosphorus load and food matrix on postprandial serum phosphate in hemodialysis patients: a pilot study

Background: Potential dietary strategies for controlling hyperphosphataemia include the use of protein sources with lower phosphorus bioavailability such as pulses and nuts, focus on phosphorus to protein ratios and the avoidance of all phosphate additives. Methods: We conducted a controlled crossover feeding study in 8 haemodialysis (HD) patients to investigate the acute postprandial effect of a modified versus standard low phosphorus diet for one day on serum phosphate, potassium and intact parathyroid levels in prevalent HD patients. Each participant consumed the modified diet on one day and the standard diet on a second day one week apart. The modified diet included beef and less dairy, with a lower phosphorus to protein ratio, as well as plant-based protein, whole grains, pulses and nuts containing phytates which reduces phosphorus bioavailability. Both diets were tailored for each participant to provide 1.1g protein/kg ideal body weight. Participants provided fasting bloods before breakfast, a pre-prandial sample before the lunch time main meal and samples at one-hour intervals for the four hours after the lunch time main meal, for analysis of phosphate, potassium and intact parathyroid hormone (iPTH). Results: At four hours post the lunch time main meal on each study day, individuals on the modified diet had serum phosphate readings 0.30 mmol/l lower than when on the standard diet (p-value = 0.015, 95% confidence interval [CI] -0.57, -0.04). The corresponding change in serum potassium at four hours was a decrease of 0.675 mmol/l (p-value = 0.011, CI -1.25, -0.10). Conclusions: Decreases in both serum phosphate and serum potassium readings on a modified low phosphorus diet encourage further larger studies to explore the possibility of greater food choice and healthier plant-based diets in HD patients.  ClinicalTrials.gov registration: NCT04845724 (15/04/2021)

Diet and Chronic Kidney Disease

Kidney disease affects almost 15% of the US population, and prevalence is anticipated to grow as the population ages and the obesity epidemic continues due to Western dietary practices. The densely caloric Western diet, characterized by high animal protein and low fruit and vegetable content, has fueled the growth of chronic diseases, including chronic kidney disease. The glomerulus or filtering unit of the kidney is very susceptible to barotrauma, and diets high in animal protein impede the glomerulus' ability to protect itself from hemodynamic injury. High animal protein intake combined with low intake of fruits and vegetables also leads to a high net endogenous acid production requiring augmentation of ammonium excretion in order to prevent acidosis. This higher workload of the kidney to maintain a normal serum bicarbonate level may further exacerbate kidney disease progression. This article reviews the potential mechanisms whereby several key characteristics of the typical Western diet may impact kidney disease incidence and progression. Reducing animal protein intake and egg yolk and increasing intake of fruits and vegetables and fiber may prevent or delay end-stage renal disease, but few clinical trials have examined vegetarian diets for management of chronic kidney disease. More research is needed to determine optimal dietary patterns for the prevention of kidney disease and its progression.

The association of dietary phosphorus with blood pressure: results from a secondary analysis of the PREMIER trial

Inconsistent findings exist for the association between dietary phosphorus intake and blood pressure (BP). We examined the longitudinal association between urinary excretion and dietary intake of phosphorus (total, plant, animal, and added) with BP.

This is a secondary analysis of PREMIER, a randomized behavioral intervention study in adults (25–79y) with BP, measured at six months, as the primary outcome. We classified total phosphorus intake from dietary recalls into plant, animal, and added phosphorus. We modeled six month change of phosphorus intake (from 24h dietary recalls, N = 622) and excretion (from 24h urine collection, N = 564) on BP, using linear regression crude and adjusted for intervention, age, race, sex, income, education, study site, and change in energy intake (kcal/d), sodium intake (mg/d), fitness (heart rate, bpm), and DASH diet index.

Baseline phosphorus intake was 1154 mg/d (95%CI 1126, 1182) with 38%, 53%, and 10% from plant, animal, and added phosphorus, respectively. Total phosphorus intake was not associated with significant changes in BP. Increased urinary phosphorus excretion was associated with a significant increase in DBP [0.14 mmHg/100 mg (0.01, 0.28), adjusted]. In several analyses, phosphorus type (plant, animal, or added) significantly modified the association between phosphorus intake and BP. For example, added phosphorus (but not plant or animal) was associated with increases in SBP and DBP, 1.24 mmHg/100 mg (0.36, 2.12) and 0.83 mmHg/100 mg (0.22, 1.44), respectively, crude.

These findings suggest that the type of phosphorus may modify the association between phosphorus intake and BP. Trial registration (clinicaltrials.gov).

Phosphate, the forgotten mineral in hypertension

PURPOSE OF REVIEW

The purpose of this study is to review the current literature related to the role of inorganic phosphate in the pathogenesis of hypertension.

RECENT FINDINGS

An increasing number of publications have revealed a detrimental role of inorganic phosphate, which is commonly used as a flavor enhancer or preservative in the processed food, in promoting hypertension in otherwise healthy individuals. Animal experimental data indicate that dietary phosphate excess engages multiple mechanisms that promote hypertension, including overactivation of the sympathetic nervous system, increased vascular stiffness, impaired endothelium-dependent vasodilation, as well as increased renal sodium absorption or renal injury. These effects may be explained by direct effects of high extracellular phosphate levels or increase in phosphaturic hormones such as fibroblast growth factor 23, or downregulation of klotho, a transmembrane protein expressed in multiple organs which possess antiaging property.

SUMMARY

Dietary phosphate, particularly inorganic phosphate, is an emerging risk factor for hypertension which is ubiquitous in the western diet. Large randomized clinical trials are needed to determine if lowering dietary phosphate content constitutes an effective nonpharmacologic intervention for prevention and treatment of hypertension.

Effect of acute high-phosphate intake on muscle metaboreflex activation and vascular function

Increased consumption of inorganic phosphate (Pi), an abundant ingredient in processed foods, has been associated with elevated cardiovascular disease risk; however, studies investigating underlying mechanisms are limited. Recently, high dietary Pi was shown to exaggerate the pressor response to static muscle contraction in rodents in part because of overactivation of metabolically sensitive skeletal muscle afferents. Whether acute high Pi consumption affects muscle metaboreflex activation in humans remains unknown. Furthermore, although acute high Pi consumption has been shown to impair vascular function in young healthy men, equivocal results have been reported. Therefore, we hypothesized that acute high Pi consumption augments mean arterial pressure (MAP) responses during muscle metaboreflex activation, impairs endothelial function, and increases arterial stiffness in young healthy men. Subjects performed 35% maximal voluntary contraction static handgrip (HG), followed by postexercise ischemia (PEI) to isolate muscle metaboreflex activation. Resting flow-mediated dilation (FMD) and arterial stiffness were assessed. Measures were made before (pre) and 60 min after (post) subjects consumed either a high-phosphate drink (2,000 mg phosphorus and 1,520 mg sodium) or a sodium drink (1,520 mg sodium; control). MAP responses during HG (preΔ = +23 ± 3 mmHg; postΔ = +21 ± 2 mmHg; P = 0.101) and PEI (preΔ = +21 ± 4 mmHg; postΔ = +18 ± 3 mmHg; P = 0.184) were similar before and after Pi consumption. In contrast, FMD was significantly attenuated following Pi (pre = 5.1 ± 0.5%; post = 3.5 ± 0.5%; P = 0.010), whereas arterial stiffness remained unchanged. There were no changes in any measured variable after control drink consumption. In summary, although the muscle metaboreflex remains unaffected following acute high Pi consumption in young healthy men, endothelial function is impaired. NEW & NOTEWORTHY This study was the first to investigate the influence of acute high-phosphate consumption on the pressor response during isometric handgrip and isolated muscle metaboreflex activation during postexercise ischemia in young healthy humans. We demonstrated that a single high dose of phosphate (2,000 mg) did not augment blood pressure in response to exercise or isolated muscle metaboreflex activation, but endothelial function was blunted in young healthy men.

The Percentage of Dietary Phosphorus Excreted in the Urine Varies by Dietary Pattern in a Randomized Feeding Study in Adults

BACKGROUND

Urinary phosphorus excretion has been proposed as a recovery biomarker of dietary phosphorus intake. However, it is unclear whether phosphorus excretion is constant across a range of dietary and nondietary factors.

OBJECTIVE

We assessed whether percentage urinary phosphorus excretion is constant across 3 dietary patterns in the Dietary Approaches to Stop Hypertension (DASH) trial.

METHODS

DASH is a completed feeding study of 459 prehypertensive and stage 1 hypertensive adults (52% male, 56% black). After a 3-wk run-in on a typical American (control) diet, participants were randomly assigned to the control diet, a diet rich in fruits and vegetables (FV diet), or a diet rich in fruits, vegetables, and low-fat dairy with reduced saturated fat and cholesterol (DASH diet) for 8 wk. We estimated the percentage phosphorus excretion as urinary phosphorus excretion (from 24 h urine) divided by phosphorus intake (from analyzed food composites). Differences between group means for all 3 diets were compared by ANOVA followed by pairwise comparisons with Tukey's honest significant difference test.

RESULTS

At the end of the intervention, the mean phosphorus intake was 1176 mg/d (95% CI: 1119, 1233 mg/d), 1408 mg/d (1352, 1464 mg/d), and 2051 mg/d (1994, 2107 mg/d) in the control, FV, and DASH diet, respectively (P < 0.001, all comparisons). The mean phosphorus excretion was 734 mg/d (682, 787 mg/d), 705 mg/d (654, 756 mg/d), and 872 mg/d (820, 923 mg/d) in the control, FV, and DASH diet, respectively (P = 0.74 control vs. FV, P < 0.001 all other comparisons). The mean percentage phosphorus excretion was 63% (60%, 67%), 51% (48%, 54%), and 43% (39%, 46%) in the control, FV, and DASH diet, respectively (P < 0.001, all comparisons).

CONCLUSIONS

These findings in prehypertensive and stage 1 hypertensive adults strongly suggest that urinary phosphorus excretion should not be used as a recovery biomarker for dietary phosphorus intake, given the wide range of urinary phosphorus excretion across dietary patterns. This trial is registered at clinicaltrials.gov as NCT0000054.

Dietary phosphorus intake and blood pressure in adults: a systematic review of randomized trials and prospective observational studies

BACKGROUND

Elevated blood pressure (BP) is a major cause of preventable disease in the United States and around the world. It has been postulated that phosphorus intake may affect BP, with some studies suggesting a direct and others an inverse association.

OBJECTIVES

We systematically reviewed the literature on the association of dietary phosphorus with BP in adults and performed a qualitative synthesis.

METHODS

We included randomized and nonrandomized behavioral intervention and feeding studies (intervention studies) and prospective observational studies that measured dietary phosphorus intake or urinary phosphorus excretion and BP. We excluded studies of supplements, children, or individuals with major medical conditions. We searched PubMed, Embase, Cochrane Trials, and clinicaltrials.gov on 1 June, 2017 and 22 August, 2018. We assessed studies' risk of bias in their assessment of phosphorus exposure and BP.

RESULTS

We reviewed 4759 publications and included 14 intervention studies (2497 participants), 3 prospective observational cohorts (17,795 participants), and 2 ongoing trials. No included intervention studies were designed specifically to achieve a phosphorus contrast. Two studies found a significant positive association of dietary phosphorus with systolic BP, 4 a significant inverse association, and 8 no significant association. Four studies found a significant inverse association with diastolic BP and 10 no significant associations. Two cohorts found lower risk of incident hypertension comparing the highest with the lowest quintiles of phosphorus intake and 1 found no significant difference: HR: 0.86 (95% CI: 0.75, 0.98); HR: 0.83 (95% CI: 0.68, 1.02); and HR: 0.75 (95% CI: 0.45, 1.27), respectively.

CONCLUSIONS

We found no consistent association between total dietary phosphorus intake and BP in adults in the published literature nor any randomized trials designed to examine this association. This trial was registered at www.crd.york.ac.uk/prospero/ as CRD42017062489.

The impact of an acute oral phosphate load on endothelium dependent and independent brachial artery vasodilation in healthy males

Serum phosphate levels are associated with cardiovascular morbidity and mortality in the general population and endothelial dysfunction may be mechanistically involved. The purpose of this study was to investigate the effects of acute phosphate supplementation on endothelial-dependent (flow-mediated dilation; FMD) and -independent (glyceryl trinitrate; GTN)) vasodilation in young, healthy males. Seventeen healthy male participants (age, 23 ± 3 years) were exposed to an oral load of phosphate (PHOS; liquid supplement containing 1200 mg of phosphorous) and placebo (PLAC) over 2 experimental days. A brachial artery FMD test was performed pre-ingestion and at 20 min, 60 min, and 120 min following the ingestion of the phosphate load or the placebo. GTN tests were performed pre- and 140 min post-ingestion. Serum phosphate was not impacted differently by phosphate versus placebo ingestion (p = 0.780). In contrast, urinary phosphate excretion was markedly increased in the PHOS (p < 0.001) but not in the PLAC condition (p = 0.130) (Δ fractional excretion of phosphate in PHOS (29.2%) vs. PLAC (9.3%)). This indicates that circulating phosphate levels were homeostatically regulated. GTN-mediated vasodilation was not significantly affected by phosphate ingestion. In primary analysis no impact of phosphate ingestion on FMD was detected. However, when the shear stress stimulus was added as a covariate in a subset of participants, exploratory pairwise comparisons revealed a significantly lower FMD 20 min post-phosphate ingestion versus placebo (p = 0.024). The effects of phosphate ingestion on FMD and serum phosphate are in contrast with previous findings and the mechanisms that underlie the disparate results require further investigation.

Phosphorus Additives and Albuminuria in Early Stages of CKD: A Randomized Controlled Trial

BACKGROUND

Little is known about the effects of phosphorus additives on patients with kidney disease.

STUDY DESIGN

Randomized, double-blind, crossover trial.

SETTING & PARTICIPANTS

31 adults with early stages of presumed chronic kidney disease (estimated glomerular filtration rate ≥ 45mL/min/1.73m2; urine albumin-creatinine ratio sex-specific cutoff points: men ≥ 17mg/g, women ≥ 25mg/g).

INTERVENTION

Higher versus lower phosphorus intake for 3 weeks. Higher phosphorus intake was achieved by the addition of commercially available diet beverages and breakfast bars to diet.

OUTCOMES

Change in 24-hour urine albumin excretion and plasma fibroblast growth factor 23 level.

MEASUREMENTS

Two 24-hour urine collections and a single fasting blood draw at the end of each period.

RESULTS

Mean baseline values for phosphorus intake, 24-hour urine phosphorus excretion, and estimated glomerular filtration rate were 1,113±549 (SD) mg/d, 688±300mg/d, and 74.6±22.0mL/min/1.73m2. Median urine albumin excretion of 82.7 (IQR, 39.6-174.1) mg/d. Although phosphorus intake from study products increased by 993mg/d (P<0.001) during the higher compared to lower phosphorus additive period, background phosphorus intake decreased by 151mg/d (P=0.004). Higher phosphorus additive consumption increased 24-hour urine phosphorus excretion by 505 (95% CI, 381 to 629) mg/d (P<0.001), but did not significantly increase albuminuria (higher vs lower: 14.3%; 95% CI, -2.5% to 34.0%; P=0.1) or fibroblast growth factor 23 level (higher vs lower: 3.4%; 95% CI, -5.9% to 13.6%; P=0.4).

LIMITATIONS

Small sample size, short duration of intervention, changes in background diet during the intervention.

CONCLUSIONS

A 3-week consumption of higher phosphorus food additives did not significantly increase albuminuria. Further studies are needed to confirm these results.