The Relationship between the Dietary Inflammatory Index (DII) and Metabolic Syndrome (MetS) in Middle-Aged and Elderly Individuals in the United States

(1) Background: With the aging demographic shift in society, there is a growing number of middle-aged and elderly individuals affected by metabolic syndrome (MetS), a risk factor contributing to all causes of mortality. Inflammation plays a crucial role in the development of MetS. This study aims to examine the correlation between MetS and pro-inflammatory diets in middle-aged and elderly individuals, utilizing the Dietary Inflammation Index (DII) as a measure. (2) Methods: Data were extracted from the 2007-2016 National Health and Nutrition Examination Survey (NHANES) database for individuals who were 45 years of age or older. The DII was determined for each participant through 24-h dietary recall interviews. The relationship between DII and MetS was assessed using binary logistic regression analysis, and the association between DII and MetS-related indicators was further explored through generalized linear model (GLM) and quantile regression analysis. (3) Results: A total of 3843 middle-aged and elderly individuals were included in the study. After controlling for confounding factors, the highest quartile of DII was associated with a higher risk of MetS (ORQ4:Q1 =1.339; 95%CI: 1.013, 1.769; p for trend = 0.018). The top DII quartile also increased the risk of reduced HDL-C (ORQ4:Q1 = 1.499; 95%CI: 1.005, 2.234; p for trend = 0.048) and raised FG (ORQ4:Q1 =1.432; 95%CI: 1.095, 1.873; p for trend = 0.010) compared to the lowest DII quartile. The levels of DII were found to be positively correlated with BMI (i3 = 0.258, p = 0.001), FPG (i3 = 0.019, p = 0.049), TG (i3 = 2.043, p = 0.013), waistline (i3 = 0.580, p = 0.002), and negatively correlated with HDL-C (i3 = -0.672, p = 0.003). (4) Conclusions: In middle-aged and elderly individuals in the United States, a high DII score has been linked to the presence of MetS, low HDL-C, and hyperglycemia. Therefore, dietary recommendations for the middle-aged and elderly should focus on reducing the DII by choosing foods rich in antioxidants, dietary fiber, and unsaturated fatty acids.