Dietary Total Polyphenol, Flavonoid, and Lignan Intakes Are Associated with Obesity and Diabetes-Related Traits: A Case-Control Study.

Dietary phytochemicals have been under examination as adjuvants for the prevention and treatment of obesity and diabetes. This study aimed at examining the potential associations of dietary "Phytochemical Index" (PI) and polyphenol intake with obesity and diabetes-related parameters. The case-control study involved 331 participants (156 overweight/obese and 175 normal weight), aged 18-50 years. Dietary intake was assessed using the 24-hr dietary recall method, and the PI score was calculated as the percentage of energy intake provided by phytochemical-rich foods. Polyphenol intakes were calculated using Phenol-Explorer and U.S. Department of Agriculture databases. Anthropometrical measurements were taken, serum glucose, insulin, and lipid profiles were analyzed, homeostatic model assessment for insulin resistance (HOMA-IR) was calculated, and blood pressure was measured. Linear regression analyses were used to examine the potential associations. Participants with higher PI scores had higher total and some sub-classes polyphenol intakes compared with lower ones ( < 0.05, for each). Dietary PI score was not associated with any of the anthropometrical measurements; however, total polyphenol and flavonoids intakes were inversely associated with body mass index ( = -0.269,  = 0.049;  = -0.262,  = 0.048; respectively), waist circumference ( = -0.127,  = 0.021;  = -0.130,  = 0.016; respectively), and waist-to-hip ratio ( = -20.724,  = 0.032;  = -22.199,  = 0.018; respectively) after adjusting for potential confounders. Either dietary PI score or total and sub-class polyphenol intakes were not associated with a better metabolic profile, except for the lignan intake, which was inversely associated with HOMA-IR ( = -0.048,  = 0.011). Higher dietary polyphenol intake may have potential in the prevention of obesity and diabetes, and validated practical tools are essential for the assessment of polyphenol intake in clinical practice.