Correlation research demonstrates that an inflammatory diet is a risk factor for calcium oxalate renal stone formation

Background and aims: Previous studies have demonstrated associations between the Dietary Inflammatory Index (DII®), an analytical tool which evaluates the inflammatory potential of the diet according to the pro- and anti-inflammatory properties of its components, and renal stone formation. However, these have not comprehensively addressed important parameters such as stone type, gender, DII scores in stone formers (SFs) and healthy controls (Cs) and associations of DII with urine and blood chemistries. These were adopted as the survey parameters for the present study, the purpose of which was to test whether the contributory role of an inflammatory diet on stone formation could be further confirmed.

Methods: 97 calcium oxalate (CaOx) SFs and 63 Cs, matched for age and gender each completed a semi-quantitative food frequency questionnaire from which nutrient composition was computed. These data were used to calculate the DII® score. To control the effect of energy intake, energy-adjusted DII scores were calculated per 1000 kcal consumed (E-DII™). A single blood sample and two consecutive overnight (8h) urine samples were collected from a subset (n = 59 SFs and n = 54 Cs) of the overall number of particpants (n = 160). These were analysed for renal stone risk factors. Data were analysed using regression models fit in R software.

Results: E-DII scores were found to fit the data better than DII, so they were used throughout. E-DII scores were significantly more positive (more pro-inflammatory) in SFs than in controls in the combined gender group (-0.34 vs. -1.73, p < 0.0001) and separately in males (-0.43 vs. -1.78, p = 0.01) and females (-0.26 vs. - 1.61, p = 0.05). In blood, a significant negative correlation was seen between E-DII and HDL cholesterol. In urine significant positive correlations were seen between E-DII and each of calcium (ρ = 0.25, p = 0.02), phosphate (ρ = 0.48, p < 0.001), magnesium (ρ = 0.33, p < 0.0001) and uric acid (ρ = 0.27, p = 0.004) concentrations. A significant negative correlation was seen between E-DII and urinary volume ρ = -0.27, p = 0.003). There was no correlation between E-DII scores and the relative supersaturations of urinary CaOx, calcium phosphate (brushite) and uric acid.

Conclusions: Our findings provide hitherto unreported quantitative evidence in support of the notion that the diet of calcium oxalate renal stone patients is significantly more pro-inflammatory than that of healthy controls.