BMI and PCOS

First, a note on the name

You'll now see the NHS call this condition PMOS, short for polyendocrine metabolic ovarian syndrome. It used to be called polycystic ovary syndrome, or PCOS, and that's still the name most people search for and many doctors use. They're the same condition. The new name reflects the fact that it affects hormones and metabolism across the whole body, not just the ovaries, and that the "cysts" were never really cysts in the first place.

It's common. International estimates put it at around 1 in 10 women of reproductive age. Symptoms vary a lot from person to person, but the NHS lists these among the main ones:

• irregular periods, or long gaps between them
• extra hair growth on the face or body, or thinning hair on the head
• weight gain, or finding it hard to lose weight
• difficulty getting pregnant
• oily skin and acne
• feeling very tired, and low mood or anxiety

How weight and PCOS feed each other

The link that matters most is insulin. Many women with PCOS have insulin resistance, which means the body has to produce more insulin than usual to keep blood sugar steady.

Those higher insulin levels push the ovaries to make more testosterone, which is behind a lot of the symptoms. Insulin also makes it easier to store fat, particularly around the middle. And carrying extra weight makes insulin resistance worse. It's a loop, and it's a big part of why PCOS can feel so unfair: the condition makes weight easier to gain, and the weight makes the condition worse.

PCOS also raises the long-term risk of type 2 diabetes, and that risk rises further with weight. That's one reason regular check-ups matter.

Why 5% is the number to remember

You don't need to reach a "perfect" BMI, or the middle of your healthy weight range, to feel a difference. The 2023 international evidence-based guideline on PCOS notes that losing 5 to 10% of your body weight can bring real benefits for women who are above a healthy weight, including more regular periods and a better chance of getting pregnant. If that's your goal, our guide to BMI and pregnancy explains what your midwife will look at.

As that last line shows, 5% might not even move you into a different BMI category. That's fine. What you're watching for is a change in your symptoms, not a change of label.

If you have PCOS and a healthy BMI

Plenty of women with PCOS are a healthy weight. It's sometimes called lean PCOS. If that's you, you may already have been told to "just lose a bit of weight" by someone who hadn't looked at your numbers, and it's not helpful advice.

Insulin resistance can still be present at a healthy BMI, and a waist measurement is often a better clue than your weight. Our guide to waist-to-height ratio explains how to check it. Beyond that, treatment should focus on whatever is affecting you most, whether that's your periods, fertility, skin or hair.

What helps

• Eating in a way you can actually keep up. There's no single PCOS diet with strong evidence behind it. Meals built around vegetables, protein and wholegrains, with fewer sugary foods and drinks, tend to help keep blood sugar steadier.
• Moving more, including strength work. Working muscles use glucose and help insulin do its job, and that benefit shows up whether or not the scales move.
• Talking to your GP about treatment. Depending on your symptoms, options can include the contraceptive pill to regulate periods, or metformin, a type 2 diabetes medicine that's sometimes used to help with weight and tiredness in PCOS.
• Keeping up with check-ups. The NHS points out that regular check-ups help reduce the risk of long-term problems like type 2 diabetes and heart disease.

What BMI can and can't tell you here

BMI is a reasonable rough guide to whether weight is likely to be making your PCOS worse. It can't show insulin resistance, hormone levels, or how your body stores fat. Put it alongside your waist measurement and any blood tests your GP arranges, and you'll have a much clearer picture.

If your family background is South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean, it's worth knowing that NICE uses lower BMI thresholds for you: overweight from 23 and obesity from 27.5. Insulin resistance tends to show up at lower weights in these groups, which is relevant with PCOS in particular. Our stone and pounds chart shows what that difference looks like in practice.