Obesity has consistently been demonstrated to have a detrimental effec
t upon the female reproductive system. This review explores the common
association of obesity with polycystic ovary syndrome (PCOS), the eff
ect of obesity on the clinical and endocrinological parameters, and th
e role of insulin resistance in the expression of this disorder. An im
provement in menstrual function, a decrease in the clinical androgenic
profile, and significant increase in spontaneous pregnancy rates have
been reported following weight loss. Obesity is associated with poor
pregnancy outcome and miscarriage in both women with PCOS, and in thos
e with normal ovarian morphology. The optimal weight gain during pregn
ancy remains controversial, but obesity is a risk factor for both mate
rnal and fetal complications, and dietary advice should be offered on
an individual basis according to the prepregnancy BMI. Weight gain at
the time of menopause is common, and dietary advice is paramount as ob
esity is an independent risk factor for thrombosis, coronary heart dis
ease (CHD), and breast and endometrial cancer. Effective nutritional c
ounselling should be offered at all stages of the female reproductive
lifecycle.