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

Not Applicable

Completed

Conditions: Albuminuria

Interventions: Other: Higher phosphorus period
Other: Lower phosphorus period

Registration Number: NCT02020785

Lead Sponsor: Geisinger Clinic

Brief Summary: 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: 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).

Recruitment & Eligibility

Status: COMPLETED

Sex: All

Target Recruitment: 31

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

Study & Design

Study Type: INTERVENTIONAL

Study Design: CROSSOVER

Arm && Interventions

Group	Intervention	Description
Higher phosphorus period	Higher phosphorus period	Commercially-available unaltered food/beverage products containing phosphorus additives (\~1gm/d of phosphorus) will be given for 3 weeks
Lower phosphorus period	Lower phosphorus period	Commercially-available unaltered food/beverage products without phosphorus additives (\<10mg/d of phosphorus) will be given for 3 weeks

Primary Outcome Measures

Name	Time	Method
24-hour Urine Albumin Excretion	3 weeks	Two 24-hour urine collections will be collected during the 3rd week of each period
Fibroblast Growth Factor-23 (FGF-23)	3 weeks	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

Secondary Outcome Measures

Name	Time	Method
Systolic Blood Pressure	2-3 weeks	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.
Diastolic Blood Pressure	2-3 weeks	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.