Dietary Phytochemical Index and Fasting Plasma Glucose in Adults with Type 2 Diabetes: A Cross-Sectional Study

Background/Objectives: Type 2 diabetes mellitus (T2D) is a major public health challenge. Phytochemicals have gained attention for their potential role in glucose regulation. This study aimed to investigate the association between dietary phytochemical intake, assessed using the Dietary Phytochemical Index (DPI), and fasting plasma glucose in adults with established T2D. Methods: A cross-sectional study was conducted among 340 adults with T2D attending the Diabetes Clinic of the General Hospital of Kalamata, Greece. Dietary intake was assessed using a validated food frequency questionnaire and DPI was calculated as the percentage of total daily energy derived from fruits, vegetables, legumes, whole grains, nuts/seeds and olives/olive oil. Multivariable linear regression was used to examine the association between DPI and fasting plasma glucose, adjusting for demographic, lifestyle, anthropometric and clinical characteristics. The fully adjusted analysis included 199 participants with complete data. Additional models adjusted for Mediterranean diet adherence, total energy intake and socioeconomic factors. Results: Each 1-percentage-point increase in DPI was associated with 0.65 mg/dL lower fasting plasma glucose (b = -0.652, 95% CI: -1.177 to -0.127; and p = 0.015). The association remained after additional adjustment for Mediterranean diet adherence, total energy intake and socioeconomic factors and was supported by multiple-imputation analysis. Food-group component analyses were exploratory; no component remained statistically significant after false discovery rate correction. Conclusions: Higher DPI was associated with lower fasting plasma glucose in adults with T2D after adjustment for measured covariates. Prospective studies and randomized trials are needed to confirm this association and determine its clinical relevance.