To determine the effect of limiting the intake of phosphate food additives on serum phosphorus levels among patients with end stage renal disease.
Study design and study population:
This was a cluster randomized (randomized by hemodialysis shift), controlled trial of 14 long-term hemodialysis facilities.
Intervention or observation:
Patients were included in the study if their most recent phosphorus and mean phosphorus over the previous 3 months were both greater than 1.77mmol/L. Two hundred and seventy-nine patients were randomized, by hemodialysis shift, to either the intervention or control group.
Patients in the intervention group received 30 minutes of face to face education about phosphorus containing food additives and were provided magnifiers for reading ingredients lists that were labelled with phosphorus-containing additives to avoid. Patients were also provided handouts about local fast food restaurants and optimal food choices. A telephone call was made to all participants one month later to reinforce education. All patients in both groups received usual care from their dietitians and nephrologists, including standard low phosphorus diet teaching.
Primary endpoint, secondary endpoint:
Primary End Point: Change in serum phosphorus level after 3 months.
Secondary Endpoints: Change in nutritional knowledge and change in reading ingredients lists and nutrition facts tables.
Intervention participants showed a modest but statistically significant 0.19mmol/L greater decline in serum phosphorus after 3 months than the control group. They also showed an increase in reading ingredients lists and nutrition facts tables. No improvement in nutritional knowledge was noted in either group.
The strength of this study is its randomized design which resulted in very similar intervention and control groups. Limitations to this study include the short duration (3 months), modest sample size and the fact that it was limited to a single geographic area. While it is possible that the control group may have been influenced by the study activities, this would have underestimated the impact of the intervention.
Impact on Practice:
Routine nutritional education should include information about phosphorus-containing food additives. As the food supply changes and the food industry shifts from sodium to other food additives, it is highly likely that the amount of dietary phosphorus from additives will continue to increase. Renal dietitians need to adjust traditional teaching tools to include information about phosphate additives. Nutrition education on phosphate additives is a low cost, low risk and effective intervention.