Vegetarian compared with meat dietary protein source and phosphorus homeostasis in chronic kidney disease

Abstract

Background and objectives: Patients with advanced chronic kidney disease (CKD) are in positive phosphorus balance, but phosphorus levels are maintained in the normal range through phosphaturia induced by increases in fibroblast growth factor-23 (FGF23) and parathyroid hormone (PTH). This provides the rationale for recommendations to restrict dietary phosphate intake to 800 mg/d. However, the protein source of the phosphate may also be important.

Design, setting, participants, & measurements: We conducted a crossover trial in nine patients with a mean estimated GFR of 32 ml/min to directly compare vegetarian and meat diets with equivalent nutrients prepared by clinical research staff. During the last 24 hours of each 7-day diet period, subjects were hospitalized in a research center and urine and blood were frequently monitored.

Results: The results indicated that 1 week of a vegetarian diet led to lower serum phosphorus levels and decreased FGF23 levels. The inpatient stay demonstrated similar diurnal variation for blood phosphorus, calcium, PTH, and urine fractional excretion of phosphorus but significant differences between the vegetarian and meat diets. Finally, the 24-hour fractional excretion of phosphorus was highly correlated to a 2-hour fasting urine collection for the vegetarian diet but not the meat diet.

Conclusions: In summary, this study demonstrates that the source of protein has a significant effect on phosphorus homeostasis in patients with CKD. Therefore, dietary counseling of patients with CKD must include information on not only the amount of phosphate but also the source of protein from which the phosphate derives.

Trial registration: ClinicalTrials.gov NCT00764816.

Figure 1.

Overall study design: The top panel demonstrates the overall crossover design, and the lower panel depicts urine and blood sampling during the 24-hour Indiana Clinical Research Center (ICRC) inpatient stay.

Figure 2.

Diurnal variation of blood and urine studies on Vegetarian compared with Meat Diet: Subjects were admitted to the Indiana Clinical Research Center for 24 hours at the end of each 7-day diet period. Timed urine and blood samples were collected. The diurnal variation for blood levels of phosphorus (A), calcium (B), intact PTH (C), and the urine fractional excretion of phosphorus (FEPhosph, D) are graphed for the two diets with mean ± SE. The timing of the meals are depicted as B = breakfast, L = lunch, and D = dinner. The diurnal variation was similar for the two diets. However, the phosphorus, calcium, and FEphosph were all higher for the meat diet compared with the vegetarian diet, and the PTH was lower.

Figure 3.

Relationship between 24-hour urine and fasting 2-hour urine for FEphosphorus. This graph demonstrates the relationship between the 24-hour urine FEphosph and the morning 2-hour random FEphosph. The regression curves are demonstrated for each of the diets. ●, meat diet; ○, vegetarian diet.