Dietary Fiber Intake, Food Sources, and Their Associations with Metabolic Parameters in Adults

Background/Objectives: Dietary fiber intake is associated with lower risk of several chronic diseases; however, intake levels remain below recommended values in many populations. This study aimed to evaluate dietary fiber intake, major fiber sources, and their associations with sociodemographic and metabolic parameters in adults. Methods: This cross-sectional study included 820 adults (mean age 33.63 ± 13.58 years) attending the family medicine outpatient clinic. Dietary intake was assessed using a food frequency questionnaire. Fiber intake was evaluated as total intake and by source (whole-food and refined carbohydrate-rich foods). Sociodemographic, anthropometric, and metabolic data were also collected and analyzed. Results: Mean dietary fiber intake was 13.42 g/day, well below recommended levels. Fiber intake and its sources differed significantly across age groups (p < 0.05); younger adults consumed more fiber from refined carbohydrate-rich foods, whereas fruit- and vegetable-derived fiber increased with age. Women consumed more fiber from whole-food sources, whereas men consumed more fiber from refined carbohydrate-rich foods. Whole-food fiber intake was inversely associated with fasting insulin (r = -0.099) and Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) (r = -0.094) in unadjusted analyses, but these associations were not significant after multiple-testing correction. In the adjusted model, total dietary fiber intake remained inversely associated with HOMA-IR (β = -0.148, p = 0.007). Conclusions: The findings highlight the importance of considering dietary fiber sources when evaluating associations between dietary fiber intake and metabolic parameters. Although associations between whole-food fiber intake and glycemic markers were attenuated after multiple-testing correction, total dietary fiber intake remained independently associated with HOMA-IR. Prospective longitudinal studies are needed to confirm these findings and clarify possible causal relationships.