Polycystic ovary syndrome is a common disease that affects 1 out of 16 women. Metabolic and endocrine abnormalities seen in PCOS include insulin resistance, androgen excess and infertility. This study focuses on the insulin resistance aspect because increased insulin resistance leads to premature onset of impaired glucose tolerance or diabetes whereas decreased insulin resistance reduces androgen excess, improves the ovarian function and increases fertility. Although insulin resistance can be treated with insulin-sensitizing drugs, PCOS clinically manifests during adolescence and the long-term safety of the drug-treatment can be a concern. Thus, improving insulin resistance with effective nutritional approaches would be very desirable. Epidemiological studies and animal experiments suggest that replacement of dietary saturated fats with monounsaturated (MUFA) and polyunsaturated (PUFA) fats improves insulin resistance.