PCOS and insulin resistance: the mechanism behind most symptoms
Why insulin sits underneath so much of PCOS, how it is assessed, and what changes it - including for women at a normal weight.
If one mechanism explains why symptoms cluster the way they do, it is insulin.
In short: Many women with PCOS have some degree of insulin resistance, independent of body weight. Higher circulating insulin increases ovarian androgen production and lowers sex hormone binding globulin, which raises free testosterone. That drives acne, hirsutism and disrupted ovulation.
The chain of events
means cells respond less efficiently to insulin, so the pancreas produces more. Elevated insulin has two effects that matter here: it stimulates the ovaries to produce more androgens, and it suppresses production of sex hormone binding globulin in the liver. Less binding globulin means more free, active testosterone.
More androgen activity disrupts follicle development, so ovulation becomes irregular. It also produces the skin and hair changes. One mechanism, several symptoms.
It is not only about weight
This is the part that gets missed. Insulin resistance occurs in lean women with PCOS too. Weight-focused advice given to a woman with a normal BMI is both unhelpful and inaccurate, and it is a common reason women disengage from care.
How it is assessed
Fasting insulin is not routinely measured in the NHS. In practice you are more likely to be offered HbA1c or an oral glucose tolerance test, plus a lipid profile. Low sex hormone binding globulin and clinical signs such as dark velvety skin patches also point towards it.
What changes it
Resistance training. Muscle is the main site of glucose disposal. Two to three sessions a week has meaningful effects on insulin sensitivity, independent of weight change.
Walking after meals. Ten to fifteen minutes after eating measurably reduces post-meal glucose. Small, repeatable, effective.
Meal composition. Protein and fibre alongside carbohydrate slows the glucose rise. This is more useful than eliminating carbohydrate, which is hard to sustain and often backfires.
Sleep. Short sleep worsens insulin sensitivity within days. It is not a soft factor.
Metformin. Prescribed for some women with PCOS where insulin resistance is significant, sometimes alongside cycle or fertility treatment. A clinical decision, not a supplement.
Inositol. Has some supportive evidence in PCOS, though it is less well established than the above. Discuss with a clinician rather than self-prescribing.
Why it matters long term
PCOS is associated with higher risk of type 2 diabetes and gestational diabetes. Periodic metabolic screening is a reasonable part of ongoing care, not an over-reaction.
Common questions
Do I need to cut carbohydrate? No. Composition, portion and timing generally beat elimination, and restrictive eating carries its own risk in a group already prone to disordered eating.
Will metformin help me lose weight? It is not a weight loss drug, though some women see modest change. Its role is metabolic.
Can insulin resistance be reversed? Sensitivity can improve substantially with training, nutrition and sleep.
This is information, not medical advice.
Read the full PCOS guide.