Association between Diet Quality Index-International and the odds of polycystic ovary syndrome: a case–control study

Background Polycystic ovary syndrome (PCOS) is the most common endocrine-metabolic disorder in women of reproductive age, associated with reproductive, metabolic, and psychological complications. Given the role of lifestyle factors in the pathophysiology of PCOS, dietary patterns have gained attention as modifiable determinants. However, previous studies have mostly focused on specific dietary indices, and the association between a comprehensive diet quality index and PCOS risk remains unclear. This study aimed to investigate the association between a comprehensive diet quality index and the odds of PCOS using a case–control design. Method This case–control study enrolled 300 women (150 PCOS cases and 150 healthy controls) aged 20–35 years from Umm Al-Qura University Hospital. Dietary intake was assessed using a validated FFQ, and diet quality was measured by the Diet Quality Index-International (DQI-I) (score 0–100). Anthropometrics and physical activity were recorded. Logistic regression, adjusted for age, body mass index, smoking status, dietary fiber intake, physical activity, and total energy intake, was used to evaluate the association between DQI-I tertiles and PCOS risk, with p < 0.05 considered significant. Results PCOS cases had higher BMI (29.1 vs. 27.0 kg/m 2 , p = 0.044) and lower DQI-I scores (68.0 vs. 70.0, p < 0.001) than controls, with lower intakes of fruits, vegetables, and low-fat dairy ( p < 0.05) but higher MUFA and PUFA ( p < 0.05). In adjusted logistic regression, the highest DQI-I tertile was associated with 70% lower odds of PCOS versus the lowest tertile (OR = 0.30, 95% CI: 0.16–0.56, P for trend <0.001), while the middle tertile was non-significant (OR = 0.78, 95% CI: 0.47–1.28). Discussion Our findings demonstrated that overall diet quality, as measured by the DQI-I, was significantly lower among women with PCOS compared to healthy controls. This reduced diet quality remained independently and inversely associated with the odds of PCOS after adjustment for age, BMI, smoking, fiber, physical activity, and energy intake. Notably, women in the highest DQI-I tertile had approximately 70% lower odds of PCOS compared with those in the lowest tertile, an association that is both statistically robust and clinically meaningful.