New Findings on Diet and Kidney Disease

Research presented at Kidney Week 2014 highlights dietary factors affecting kidney disease outcomes—including a study reporting that a “healthy diet” and lower sodium intake are associated with a reduced risk of major renal outcomes. Another report draws attention to the potentially high levels of potassium added to some “reduced-sodium” foods.

Nephrologist Andrew Smyth, MB, of National University of Ireland Galway and his colleagues presented the results from the Diet and Health Study of the National Institutes of Health and the American Association of Retired Persons. On the basis of findings on food frequency questionnaires completed by nearly 545,000 participants, the researchers evaluated the relationship between diet quality, sodium and potassium intake, and major renal outcomes—dialysis or death from renal causes. The study evaluated several different definitions of a “healthy diet”: the Healthy Eating Index, the Alternate Healthy Eating Index, the Mediterranean Diet Score, and the Recommended Food Score, along with sodium and potassium intake.

On three of four diet quality measures, a healthy diet was associated with a lower risk of dialysis or death from a renal cause; there was no association with the Recommended Food Score. On multivariate analysis, the risk of the combined outcome was 16 to 23 percent lower for participants in the highest quintile of dietary quality, compared with the lowest quintile.

Said Smyth: “We found that high sodium intake, average 4.7 g/day, was associated with an increased risk, but no difference between low and moderate intakes: average 2.0 and 3.1 g/day.” High potassium intake was associated with a reduced risk.

The risk was 19 percent higher for participants in the highest quintile of sodium/potassium ratio. The researchers conclude, “Our findings extend the known benefits of healthy eating and show that the consumption of a healthy diet, including reducing sodium intake from high levels and increasing potassium intake, may protect from future major renal endpoints.”

Arti Sharma Parpia, RD, of St. Michael’s Hospital, Toronto, and colleagues from the University of Toronto evaluated the protein, sodium, phosphorus, and potassium content of “reduced-sodium” meat and poultry products sold at grocery stores. “Food manufacturers may use phosphate and potassium additives to replace the functional and flavor properties of sodium, and the amount is usually not listed on food labels,” the researchers write.

They found that sodium-reduced products contained 25 to 55 percent less sodium than their non–sodium-reduced counterparts: the mean difference was 460 mg per 100 g. The sodium-reduced products also contained on average 47 percent more potassium, with a wide variability in potassium content: from 210 to 1500 mg per 100 g. Potassium-containing additives were found on the ingredients list of 63 percent of sodium-reduced products, compared with 25 percent of non–sodium-reduced products.

Phosphorus and protein levels did not differ for the two groups of products. “Potassium additives are frequently added to sodium-reduced meat and poultry products in amounts that significantly contribute to the potassium load for CKD patients,” the researchers conclude. “Patients requiring a potassium restriction should limit their intake of sodium-reduced meat and poultry products.”