Validation of the Westernized Diet Index (WDI) through inflammatory, oxidative stress, and metabolic biomarkers and its association with overweight/obesity-evidence from a case-control study

The global rise in obesity is linked to Western dietary patterns (WDPs). The Westernized Diet Index (WDI) was developed to measure adherence to WDPs. This study examined the associations between the WDI and overweight/obesity and constructively validated the findings against inflammatory, oxidative stress, and metabolic biomarkers. A population-based case-control study was conducted on 1605 adults (812 overweight/obese; 793 normal weight), using a 124-item validated food frequency questionnaire to assess dietary intake and calculate WDI-G (global Z-score) and WDI-FG (food group Z-scores). Fully adjusted logistic and linear regression models evaluated associations with BMI and biomarkers. In fully adjusted models, a 1-unit increase in WDI-G (ranging from −1.71 to 1.02) was associated with a 41% decrease in the odds of overweight/obesity (OR = 0.59; p = 0.007), and similarly, a 1-unit increase in WDI-FG (ranging from −1.91 to 1.44) was linked to a 26% decrease in the odds of overweight/obesity (OR = 0.74; p = 0.086). Higher WDI-G scores were also significantly associated with lower waist circumference (−4.6 cm), fasting blood glucose levels (−7.6 mg dL⁻¹), and LDL-c levels (−7.1 mg dL⁻¹) and higher plasma malondialdehyde levels (+0.35 μM). Similarly, higher WDI-FG scores were associated with lower plasma IL-6 (−37.8 pg mL⁻¹), lower triglyceride (−15.3 mg dL⁻¹), and higher HDL-c (+2.37 mg dL⁻¹) levels. Lower adherence to the WDP diet was associated with lower odds of having overweight/obesity and more favorable metabolic, inflammatory, and oxidative stress profiles. These findings support the use of the WDI as a valid and practical nutritional tool for assessing WDPs in clinical nutrition, nutritional epidemiology, and public health research.