BMJ Group Medical Reference
This information is for people who have polycystic ovary syndrome. It tells you about losing weight, a treatment used for polycystic ovary syndrome. It is based on the best and most up-to-date research.
Does it work?
Losing weight may help reduce unwanted hair and improve how your body uses insulin. We don't know for certain if losing weight will help you get periods more regularly. That's because there isn't much research looking at this. But many doctors recommend you try this before any other treatment, and lots of women with polycystic ovary syndrome (PCOS) say it can be helpful.
But losing weight will work only if you are overweight. Don't try to lose weight if you're already at a healthy weight.
What is it?
To lose weight, you need to eat fewer calories than you use up through the day. It sounds simple, but it can be very hard to do.
There are lots of diets intended to help you lose weight. But the key thing is to eat fewer calories than you use. Calories are a way of measuring the amount of energy in food. You can use up more calories by taking regular exercise.
About half of all women with PCOS are overweight. If you're not sure whether you need to lose weight, you could ask your doctor.
When doctors talk about a 'healthy' or 'ideal' weight, they mean a weight that lowers your risk of getting serious health problems, such as heart disease or high blood pressure. It's not based on how thin you would like to look. 
Most doctors use the body mass index (BMI for short) to work out whether you're at a healthy weight. Your BMI is a number that's worked out from your height and weight. You can work out your own BMI. This table shows what the different BMI scores mean. 
|BMI ||What it means|
|Less than 18.5||Underweight|
|18.5 to 24.9||Healthy weight|
|25 to 29.9||Overweight|
|30 and above||Obese|
We don't know what the best diet is if you have PCOS and want to lose weight, but it has to be one that you can stick to. Some doctors think that eating more fibre and less saturated fat (such as butter and animal fat) may be particularly helpful for women with PCOS, but there hasn't been much research on this.   You may find that losing weight in a group, such as Weight Watchers, is helpful. If you don't know how to start losing weight, ask your doctor if you can see a dietitian who has experience of working with women who have PCOS. For more information on how to lose weight if you are very overweight (obese), see our information on Obesity.