Study of Dietary Additive Phosphorus on Proteinuria and Fibroblast Growth Factor-23

Study Overview
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Brief Summary
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Phosphorus-based food additives are commonly used by food manufacturers for many applications, such as enhancing flavor, in ready-to-eat foods and beverages. While these additives can significantly increase an individual's daily phosphorus intake, little is known about the effect of dietary phosphorus on kidney health. In this study, the investigators will first lower baseline phosphorus intake to about 1000mg/d by educating participants to avoid foods with phosphorus additives. Then, participants will be randomized to a higher phosphorus period ( 2gm/d) and a lower phosphorus period ( 1gm/d) by providing unaltered, commercially-available food/beverage products with and without phosphorus additives. The investigators hypothesize that participants will have higher urine albumin excretion and fibroblast growth factor-23 (FGF-23) during the higher phosphorus period compared to the lower phosphorus period.

Detailed Description
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The Study of Dietary Additive Phosphorus on Proteinuria and FGF-23 (SODA-POP) was a single-center, randomized, double-blind, two-period cross-over study that examined the effect of higher vs. lower phosphorus intake for 3 week periods, achieved by addition of commercially available diet beverages and breakfast bars to diet on albuminuria and fibroblast growth factor 23, in adults with presumed early chronic kidney disease (estimated glomerular filtration rate >= 45 ml/min/1.73m2; and urine albumin/creatinine ratio >=17 mg/g for men or >=25 mg/g for women).

Official Title
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Randomized Cross-over Study Examining the Effects of Phosphorus Additives on Urinary Albumin Excretion and Fibroblast Growth Factor-23

Conditions
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Albuminuria

Intervention / Treatment
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* Other: Higher phosphorus period
* Other: Lower phosphorus period


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Adults at least 21 years of age with at least microalbuminuria Exclusion Criteria: Estimated glomerular filtration rate <45ml/min/1.73m2, poorly controlled diabetes or hypertension, nephrotic syndrome, hyperparathyroidism, Paget's Disease, multiple myeloma, uncontrolled thyroid disease, chronic antacid use, use of phosphorus binders, phosphorus supplements, or high-dose vitamin D, inability to complete feeding study, investigator discretion

Ages Eligible for Study
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Minimum Age: 21 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Triple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: Higher phosphorus period<br>Commercially-available unaltered food/beverage products containing phosphorus additives ( 1gm/d of phosphorus) will be given for 3 weeks | Other: Higher phosphorus period<br>* Commercially-available unaltered food/beverage products containing phosphorus additives ( 1gm/d of phosphorus) will be given for 3 weeks. All participants at the beginning of the study will receive dietary education to reduce their baseline consumption of phosphorus to a goal of  1gm/d by receiving education on avoiding phosphorus-based additives.<br>|
| Placebo Comparator: Lower phosphorus period<br>Commercially-available unaltered food/beverage products without phosphorus additives (<10mg/d of phosphorus) will be given for 3 weeks | Other: Lower phosphorus period<br>* Commercially-available unaltered food/beverage products without phosphorus additives (<10mg/d of phosphorus) will be given for 3 weeks. All participants at the beginning of the study will receive dietary education to reduce their baseline consumption of phosphorus to a goal of  1gm/d by receiving education on avoiding phosphorus-based additives.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| 24-hour Urine Albumin Excretion | Two 24-hour urine collections will be collected during the 3rd week of each period | 3 weeks | 
| Fibroblast Growth Factor-23 (FGF-23) | Plasma FGF-23 will be measured at the end of each 3 week period in the morning after an overnight fast. As this is a small pilot study, we will not adjust for multiple comparisons. A p value<0.05 will be considered statistically significant for both outcomes | 3 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Systolic Blood Pressure | Blood pressure was measured at the end of weeks 1, 2, and 3. At each visit, 3 readings were obtained in the seated position by trained and certified observers after 5 minutes of rest with an Omron HEM-907 device (Omron Healthcare Inc, Bannockburn, Ill) using a standardized protocol. We used the average of all blood pressure measurements at the end of weeks 1, 2, and 3 for each period. | 2-3 weeks | 
| Diastolic Blood Pressure | Blood pressure measured at the end of weeks 1, 2, and 3. At each visit, 3 readings were obtained in the seated position by trained and certified observers after 5 minutes of rest with an Omron HEM-907 device (Omron Healthcare Inc, Bannockburn, Ill) using a standardized protocol. We used the average of all these readings taken during end of weeks 1, 2, and 3 for each period. | 2-3 weeks | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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proteinuria