By Kirstie Vesseur, Registered Clinical Nutritionist (CNA), Legacy Nutrition, NZ and Australia.
Your periods turn up when they feel like it, if at all. There is acne along your jaw that should have stayed in your teens, hair where you do not want it, and thinning where you do. Then someone hands you a diagnosis and a script for the pill, and you are left wondering: why do I have PCOS, and what is actually going on underneath?
First, a quick note on the name. In May 2026 an international consensus published in The Lancet renamed polycystic ovary syndrome (PCOS) as polyendocrine metabolic ovarian syndrome (PMOS). The new name reflects that this is a hormonal and metabolic condition, not a condition of ovarian cysts. The change is being phased in, so you will still see "PCOS" on lab forms. I use both names here.
PMOS affects around 1 in 8 women of reproductive age (the international guideline puts it at 10 to 13 percent). The "cysts" seen on an ultrasound are usually small follicles that have not gone on to release an egg. They are a downstream effect, not the cause.
How PCOS (PMOS) is diagnosed
In adults, PCOS is diagnosed when you have two of these three features, once other causes have been ruled out:
Irregular or absent ovulation (irregular cycles)
High androgens, either on a blood test or as signs such as excess facial or body hair and acne
Polycystic ovaries on ultrasound, or a raised AMH (anti-Müllerian hormone) blood test, which can now be used instead of an ultrasound in adults (not on its own, and not in teenagers)
What pushes a woman into that pattern varies, so in clinic I look for which driver is loudest for her.
Why do I have PCOS? The main drivers
Genes
PMOS runs in families, and genetic studies link it to genes involved in hormone signalling and insulin action. Genes load the dice; food, sleep and stress influence how they play out.
Insulin resistance
This is one of the most important drivers. When your cells stop responding well to insulin, the pancreas makes more of it to compensate. High insulin encourages the ovaries to make more androgens such as testosterone, and it lowers SHBG (sex hormone binding globulin), so more of that testosterone is free and active. The result can be disrupted ovulation, irregular cycles, and unwanted skin and hair changes.
You do not have to be in a larger body to have insulin resistance. Research using the gold standard test (the insulin clamp) has found insulin resistance in most women with PCOS, lean women included. The international guideline also notes that women with PCOS have a higher risk of prediabetes and type 2 diabetes regardless of age or weight.
Low-grade inflammation
Many women with PMOS show signs of chronic, low-grade inflammation. Inflammation and insulin resistance tend to feed each other, which is one reason an anti-inflammatory way of eating sits in almost every plan I write for PMOS.
The adrenal androgen pattern
For some women, the raised androgen is mainly DHEA-S, which is made mostly by the adrenal glands rather than the ovaries. It can be missed if only testosterone is measured, so it is worth asking about if your testosterone is normal but your symptoms say otherwise.
What about the pill?
The pill does not cause PMOS, but it can mask it. It raises SHBG and lowers the ovaries' androgen production, so symptoms often settle while you take it and reappear when you stop, sometimes just as you start trying to conceive. You can read more in my article on what hormonal birth control does to your body.
Tests worth asking about
Based on the 2023 international PCOS guideline, these are the tests worth discussing with your GP:
Total testosterone and free testosterone (or the free androgen index, calculated from testosterone and SHBG)
DHEA-S and androstenedione, if testosterone is not raised but symptoms suggest high androgens
A 75 g oral glucose tolerance test (OGTT), which the guideline names as the most accurate test of blood sugar control in PCOS, whatever your weight. Fasting glucose and HbA1c are less accurate alternatives
A lipid panel (cholesterol, LDL, HDL and triglycerides), as PCOS is linked with higher cardiovascular risk
TSH, prolactin, FSH and, where relevant, 17-hydroxyprogesterone, to rule out other conditions that can look like PCOS
Two things to know. First, the guideline does not recommend routine fasting insulin tests, because the assays are not standardised enough to guide care. Second, androgen results are hard to interpret while you are on the pill. If testing is essential, the guideline suggests stopping the pill for at least 3 months with other contraception in place, which is a decision to make with your doctor, not on your own.
If your results have come back "normal" but you still feel unwell, my New Zealand Optimal Ranges Guide explains where results sit within the lab range.
The pill can be a helpful option for irregular cycles and excess hair, and metformin is often considered, particularly for women with a BMI of 25 or over. Neither replaces the food and lifestyle foundations below, and please do not stop or change any prescribed medication without talking to your GP first.
How nutrition can help
The guideline is clear that no single diet beats another for PCOS. What matters is a healthy pattern you can keep up. Here is the practical version I use with clients.
Build each meal to steady blood sugar
Protein at every meal, a whole hand of protein (about 20 to 30 g): three eggs, 100 to 120 g of chicken, fish or lean red meat, 150 to 200 g of firm tofu, or a cup of high-protein (strained) Greek yoghurt
Half the plate as vegetables, especially leafy greens and crucifers such as broccoli, cabbage and cauliflower
Slow carbohydrates in a cupped-hand portion: kūmara, lentils, chickpeas, rolled oats, brown rice or wholegrain bread, never on their own
Healthy fats: extra virgin olive oil, avocado, nuts and seeds
Extra fibre: 1 to 2 tablespoons of ground flaxseed or chia stirred into breakfast is an easy win
Bring the inflammation down
Aim for oily fish such as salmon, sardines or mackerel two to three times a week, plenty of colourful vegetables and berries, herbs and spices, and fewer ultra-processed foods and sugary drinks. If you need meal ideas, Legacy's Kitchen is full of gluten free, dairy free, high-protein recipes.
Supplements: what the evidence says
Myo-inositol. Trials commonly use 2 g of myo-inositol twice daily (4 g a day), or a 40:1 myo- to D-chiro-inositol combination. The 2023 guideline says inositol can be considered, with low risk of harm and possible benefits for metabolic markers, but limited evidence for ovulation, excess hair or weight, and it does not yet recommend any specific type, dose or ratio. For women trying to conceive, the guideline treats inositol as experimental, so discuss it with your fertility specialist.
Omega-3 fish oil, if you rarely eat oily fish. Pooled trials suggest omega-3 may improve insulin resistance and blood fats in PCOS, although the studies are small. A typical dose is 1 to 2 g of combined EPA and DHA daily with food (check the label: a 1,000 mg fish oil capsule often contains only about 300 mg of EPA and DHA).
Inositol can lower blood sugar and fish oil can affect bleeding, so check with your GP or pharmacist before starting either if you take medication (including metformin or blood thinners), are pregnant or breastfeeding. If you are pregnant, choose a standard fish oil rather than cod liver oil (which contains vitamin A), and tell your health team about any supplements before surgery.
Lifestyle matters more than you would think
Movement. Muscle is your body's biggest glucose sink. The guideline recommends 150 to 300 minutes a week of moderate activity (such as brisk walking) or 75 to 150 minutes of vigorous activity, plus muscle-strengthening work on 2 non-consecutive days. A 10 to 15 minute walk after dinner is a good place to start.
Stress and mood. Anxiety and low mood are very common with PMOS and deserve proper support in their own right. If you are running on empty, my free 7 Day Nervous System Reset is a gentle place to start.
Sleep. Women with PMOS have higher rates of obstructive sleep apnoea, whatever their weight. If you snore and wake unrefreshed or are sleepy during the day, mention it to your GP.
Higher androgens can also show up as thinning hair on the scalp. If that is part of your picture, read my article on why your hair might be falling out.
Frequently asked questions
Can PCOS go away?
PMOS is usually a long-term pattern rather than something that disappears. The good news is that symptoms often improve a great deal when insulin, inflammation, sleep and stress are supported, and many women go on to have regular cycles and healthy pregnancies.
Do I need to lose weight to manage PCOS?
Not necessarily. Lean women have PMOS too, and the guideline focuses on healthy habits and preventing weight gain rather than a number on the scale. For women in larger bodies, weight change can help, but I focus on insulin sensitivity, muscle and steady blood sugar first.
Want help with this one-on-one? See how I work with women on women’s hormone support, or browse all my services.
This article is general education, not personal medical advice. Please talk with your GP before starting supplements or changing medication.
References
Teede HJ, et al. Recommendations from the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. J Clin Endocrinol Metab. 2023. https://pubmed.ncbi.nlm.nih.gov/37580314/
Teede HJ, et al. Polyendocrine metabolic ovarian syndrome, the new name for polycystic ovary syndrome: a multistep global consensus process. The Lancet. 2026. https://pubmed.ncbi.nlm.nih.gov/42119588/
Stepto NK, et al. Women with polycystic ovary syndrome have intrinsic insulin resistance on euglycaemic-hyperinsulaemic clamp. Hum Reprod. 2013. https://pubmed.ncbi.nlm.nih.gov/23315061/
Fitz V, et al. Inositol for polycystic ovary syndrome: a systematic review and meta-analysis to inform the 2023 update of the international evidence-based PCOS guidelines. J Clin Endocrinol Metab. 2024. https://pubmed.ncbi.nlm.nih.gov/38163998/
Yang K, et al. Effectiveness of omega-3 fatty acid for polycystic ovary syndrome: a systematic review and meta-analysis. Reprod Biol Endocrinol. 2018. https://pubmed.ncbi.nlm.nih.gov/29580250/
Healthify He Puna Waiora. Fish oil supplements. Accessed 2026. https://healthify.nz/medicines-a-z/f/fish-oil-supplements
