Polycystic ovary syndrome (PCOS) affects between 4%-18% of reproductive-aged women and is associated with increased risk of obesity and obesity-related disease. PCOS is associated with hyperinsulinemia, which is known to impair fat oxidation. Research shows that carbohydrates from dairy and starch-based foods cause greater postprandial insulin secretion than carbohydrates from nonstarchy vegetables and fruits. The purpose of this study was to determine whether an ad libitum 8-week low-starch/low-dairy diet would improve fasting and postprandial fat oxidation after a high saturated fat liquid meal (HSFLM) in overweight and obese women with PCOS. Prospective 8-week dietary intervention using a low-starch/low-dairy diet in 10 women (body mass index ≥25 kg/m(2) and ≤45 kg/m(2)) with PCOS. Indirect calorimetry was used at fasting and for 5 h following consumption of the HSFLM to determine respiratory exchange ratio (RER), macronutrient oxidation, and energy expenditure (EE) at week 0 and week 8. Participants had a reduction in body weight (-8.1 ± 1.8 kg, p < 0.05) and fasting insulin (-19.5 ± 8.9 μg/mL, p < 0.05) after dietary intervention; however, these were not significantly correlated with improved fat oxidation. There was a reduction in fasting RER, and fasting and postprandial carbohydrate oxidation, and an increase in fasting and postprandial fat oxidation after adjusting for body weight. There was also significant difference in incremental area under the curve from pre- to post-diet for fat (0.06 ± 0.00 g/kg per 5 h; p < 0.001) and carbohydrate oxidation (-0.29 ± 0.06 g/kg per 5 h; p < 0.001), but not for RER or EE. In conclusion, an 8-week low-starch/low-dairy diet increased fat oxidation in overweight and obese women with PCOS.