Dietary Inflammatory Index and Cardiovascular Disease Risk in Australian Adults: A Secondary Analysis of the OLIVAUS Trial

Background: The Dietary Inflammatory Index (DII®) is a commonly used tool to assess diet-related inflammation. Higher DII scores have been associated with increased cardiovascular disease risk in observational studies. However, evidence examining cardiovascular outcomes across DII levels in controlled settings remains limited. This secondary analysis examined cross-sectional differences and longitudinal associations between dietary inflammatory potential and cardiovascular outcomes in healthy Australian adults. Methods: This study used data from a double-blind randomised crossover trial, in which 50 participants consumed 60 mL/day of either extra virgin high-polyphenol olive oil (HPOO; 320 mg/kg) or low-polyphenol olive oil (LPOO; 86 mg/kg) across two 3-week intervention periods, separated by a 2-week washout. Anthropometric measures (weight, height, waist circumference, and BMI) and cardiovascular outcomes (i.e., blood pressure, lipids, oxidised LDL, and HDL cholesterol efflux capacity) were assessed at four timepoints. DII and energy-adjusted DII (E-DIITM) scores were derived from 3-day food diaries. Linear mixed-effects models were used to compare cardiovascular outcomes across repeated-measures DII tertiles (low, medium, and high), adjusting for intervention, period, sequence, age, sex and waist circumference. Results: Forty-three participants completed this study. At baseline, BMI, waist circumference, systolic blood pressure, total cholesterol, and LDL differed significantly across DII tertiles (p < 0.05). However, over time, cardiovascular outcomes did not differ between medium or high versus low DII tertiles, and no significant time-by-tertile interactions were observed (all p > 0.05). DII values remained stable, while E-DII showed modest within-person reductions during both intervention periods (mean reduction: 0.886 units vs. 0.596 units). Conclusions: In this healthy cohort, there was no evidence of a consistent association between DII and short-term differences in cardiovascular outcomes across the intervention period. These findings should be interpreted cautiously, given the observational nature of DII groupings. Longer-duration studies with greater variation in dietary inflammatory potential are warranted to clarify the relationship between DII and cardiovascular health.