BACKGROUND: Polycystic Ovary Syndrome (PCOS) affects approximately 15% of reproductive-age women and increases risk of insulin resistance, type 2 diabetes mellitus, cardiovascular disease, cancer and infertility. Hyperinsulinemia is believed to contribute to or worsen all of these conditions, and increases androgens in women with PCOS. Carbohydrates are the main stimulators of insulin release, but research shows that dairy products and starches elicit greater postprandial insulin secretion than non-starchy vegetables and fruits. The purpose of this study was to determine whether an 8-week low-starch/low-dairy diet results in weight loss, increased insulin sensitivity, and reduced testosterone in women with PCOS. METHODS: Prospective 8-week dietary intervention using an ad libitum low starch/low dairy diet in 24 overweight and obese women (BMI ≥ 25 kg/m2 and ≤ 45 kg/m2) with PCOS. Diagnosis of PCOS was based on the Rotterdam criteria. Weight, BMI, Waist Circumference (WC), Waist-to-Height Ratio (WHtR), fasting and 2-hour glucose and insulin, homeostasis model assessment of Insulin Resistance (HOMA-IR), HbA1c, total and free testosterone, and Ferriman-Gallwey scores were measured before and after the 8-week intervention. RESULTS: There was a reduction in weight (-8.61 ± 2.34 kg, p<0.001), BMI (-3.25 ± 0.88 kg/m2, p<0.001), WC (-8.4 ± 3.1 cm, p<0.001), WHtR (-0.05 ± 0.02 inches, p<0.001), fasting insulin (-17.0 ± 13.6 μg/mL, p<0.001) and 2-hour insulin (-82.8 ± 177.7 μg/mL, p=0.03), and HOMA-IR (-1.9 ± 1.2, p<0.001) after diet intervention. Total testosterone (-10.0 ± 17.0 ng/dL, p=0.008), free testosterone (-1.8 pg/dL, p=0.043) and Ferriman-Gallwey scores (-2.1 ± 2.7 points (p=0.001) were also reduced from pre- to post-intervention. CONCLUSION: An 8-week low-starch/low-dairy diet resulted in weight loss, improved insulin sensitivity and reduced testosterone in women with PCOS.