Patient preference may play bigger role in phosphorous control vs ‘healthy’ food access

Lisa Gutekunst, MSEd, RD, CSR, CDN, FNKF

Multiple studies have found an inverse relationship between socioeconomic status (SEC) and serum phosphorus (S.PO4). However, this is not the outcome found in a recent study by Potluri and colleagues.

In the “Effect of neighborhood food environment and socioeconomic status on serum phosphorus level for patients on chronic dialysis,” SEC and S. PO4 levels were evaluated on more than 258,000 patients receiving hemodialysis across the United States. No correlation between SEC and S. PO4 was found. Instead, researchers found an inverse relationship between age and S. PO4 levels.

Though well thought out and documented, the study methods fall short in multiple areas which weakens the study.

The main fault with this study is the determination of patient SEC. Instead of obtaining SEC factors from individual participants, researchers obtained SEC information of the zip code where patients lived. Neighborhood SEC has little bearing on an individual’s SEC. It is the individual receiving dialysis, not the neighborhood.

In comparison to this study, Gutiérrez and colleagues have also looked at the relationship between SEC and S. PO4 levels multiple time. In his studies, individual SEC was determined using annual income, education level, employment status and poverty-to-income ratio. By doing this, he had a truer indication of SEC.

Secondly, researchers made multiple assumptions with regard to food procurement of the participants. They assumed participants shopped within their zip codes and they did not evaluate profiles of food outlets in surrounding areas. They have no information about patients’ social lives regarding food procurement. Older patients many need assistance with grocery shopping and have family members making food choices or they may be receiving community-sponsored meals (ie, Meals on Wheels, Mom’s Meals) that are adjusted for dialysis diet restrictions.

Additionally, researchers had no insight into what foods were purchased by patients. Just because there are multiple “healthy” food outlets for a patient to shop, does not mean that the patient is choosing low phosphorus foods. Stores deemed “healthy” sell high phosphorus foods.

To understand participants’ diets, Gutiérrez utilized multiple food frequency questionnaires and 24-hour diet recalls giving him a fuller picture of the dietary PO4 sources.

Finally, only one S.PO4 level was obtained each month. Patients may have multiple S. PO4 results in a single month, and the researchers did not indicate which level was used for analysis. This brings into question the quality of the data. One dialysis unit may test S. PO4 levels once a month, bi-weekly or weekly. This must be considered when standardizing data collection. Also, S. PO4 is affected by non-nutritional factors including metabolic acidosis, poor urea kinetic results and missed treatments.

Potluri and colleagues can be congratulated for taking on the first analysis looking at SEC and S. PO4 of hemodialysis patients. Though there are many faults with their methods, their outcomes identified the need to increase education and support younger patients regarding S. PO4 management.

References:

Gutiérrez O, et. al. Lower socioeconomic status associated with higher serum phosphate irrespective of race. J Am Soc. Nephrol. 21: 1953-1960. 2010.

Gutiérrez O, et. al. Impact of Poverty on Serum Phosphate Concentration in the Third National Health and Nutrition Examination Survey. J Ren Nutr. 21: 140-148. 2011.

Gutiérrez O, et. al. Associations of socioeconomic status and processed food intake with serum phosphorus concentrations in community-living adults: The multi-ethnic study of atherosclerosis (MESA). J Ren Nutr. 22: 480-489. 2012.

Disclosures: Gutekunst reports being an employee of DaVita Inc. and a consultant for Fresenius North America.