Very-low-phosphate diets are no better than low-phosphate diets at reducing fibroblast growth factor 23 (FGF23) levels in patients on hemodialysis (HD), but they are more effective at easing hyperphosphatemia in this population, according to new study findings.

Investigators led by Kuo-Liong Chien, MD, PhD, of National Taiwan University in Taipei, conducted a randomized, controlled, crossover trial of 35 HD patients with baseline serum phosphate levels exceeding 5.5 mg/dL or from 3.5 to 5.5 mg/dL with phosphate binder use. Investigators placed patients on either a very-low-phosphate diet (phosphate-to-protein ratio of 8 mg/g) or a low-phosphate diet (phosphate-to-protein ratio of 10 mg/g for 2 days), with a 5-day washout period between the diets.

Over 2 days, the very-low-phosphate diet and the low-phosphate diet reduced mean FGF23 by a similar amount (-1020 vs -1022 pg/mL, respectively). The very-low-phosphate diet, however, lowered mean serum phosphate significantly more (3.9 vs 4.4 mg/dL), respectively, according to results published in the Clinical Journal of the American Society of Nephrology. Patients’ baseline dietary phosphorus intake was around 700 mg/d (or 12-13 mg/g phosphorus-to-protein ratio), well in line with the Kidney Disease Outcomes Quality Initiative (KDOQI) dietary phosphorus intake recommendation of 800 to 1000 mg/d.

Per protocol, none of the patients had secondary hyperparathyroidism at baseline. During both dietary interventions, the team observed no significant changes in intact parathyroid hormone or C-terminal FGF23 levels.

“Our results imply that short-term dietary phosphate restriction rapidly improves serum phosphate level and that a phosphate-restricted diet with a phosphate-to-protein ratio of 8 mg/g might be recommended for patients on dialysis with hyperphosphatemia,” Dr Chien’s team stated.

The investigators observed subpar adherence to both the very-low-phosphate and low-phosphate diets (61% and 71%, respectively), however.

Study limitations included the relatively short duration (2 days) of dietary interventions. “Any extrapolation to the effects of low phosphate diets over longer periods is not recommended,” the authors noted.

“The short study duration and lower adherence with the more restrictive diet of 8 mg/g warrant some caution in overinterpreting the additional benefit of the 8 mg/g diet to decreased serum phosphate,” Kathleen M. Hill Gallant, PhD, of Purdue University in West Lafayette, Indiana, noted in an accompanying editorial. “It is likely that adherence to the dietary prescription would be even lower over time and in free-living patients. Thus, further data are needed to determine if the additional benefit to serum phosphate would persist long term and in a clinical practice setting.”

Still, Dr Hill Gallant called the new study a valuable contribution to the nutrition literature in chronic kidney disease-mineral bone disorder.

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References

Tsai WC, Wu HY, Peng YS, et al. Short-term effects of very-low-phosphate and low-phosphate diets on fibroblast growth factor 23 in hemodialysis patients: A randomized crossover trial [published online September 13, 2019]. Clin J Am Soc Nephrol. doi:10.2215/CJN.04250419

Hill Gallant KM. Dietary phosphorus and FGF23: Is more restriction better? [published online September 19, 2019] Clin J Am Soc Nephrol. doi:10.2215/CJN.09640819