The study retrospectively analyzed 360 PCOS patients to evaluate the effect of BMI on the results of a nutritional intervention. After treatment, ovulation rate, HOMA-IR, LDL, HDL and FPG were significantly improved in all BMI groups, with the obese group having the greatest reduction in BMI (-5.8). Higher BMI (OR = 1.089) and higher HDL (OR = 1.010) were associated with better outcomes. Older age (OR = 0.993), longer duration of symptoms (OR = 0.982), family history of PCOS (OR = 0.745), ovarian enlargement (OR = 0.887) and higher number of ovarian cysts (OR = 0.882) accompanied worse outcomes. Interaction analysis showed that age moderates the positive effect of BMI (OR = 0.992) and ovarian enlargement further reduces it (OR = 0.759). Obese patients benefited the most from the intervention, especially younger patients with smaller ovarian enlargement. The findings support personalized nutritional strategies in the treatment of PCOS.