“But you’re so thin.”
If you have lean PMOS (PCOS), you’ve probably heard some version of that sentence - from family, from friends, maybe even from a doctor. It sounds like a compliment. It functions as a dismissal. And it’s built on a myth: that this condition only happens to women who carry extra weight.
Here’s the reality: depending on the population studied, roughly 20 to 30 percent of women with PMOS have a normal BMI. That’s not a rare exception. That’s millions of women - many of them told, to their face, that they can’t have the condition their own hormones say they have.
Weight was never part of the diagnosis
Go back to the diagnostic criteria - the Rotterdam criteria, used worldwide since 2003. They ask about three things: irregular or absent ovulation, elevated androgens (male-pattern hormones like testosterone), and ovarian appearance on ultrasound. Meet two of three, with other causes ruled out, and the diagnosis applies.
Read that list again. Body weight appears nowhere in it. BMI has never been a diagnostic criterion. A woman with a BMI of 20 and a woman with a BMI of 32 can both have PMOS, meet the same criteria, and need equally real care.
“BMI has never been a diagnostic criterion. It just quietly became a gatekeeping one.”
What’s actually happening in lean PMOS
The hormonal machinery of PMOS doesn’t check your weight before acting. In lean presentations, the same core disruptions show up: androgens run higher than they should, the brain-to-ovary signalling rhythm (the pulses of LH and FSH that time ovulation) gets skewed, and follicles stall mid-development - which is what shows up on an ultrasound.
And here’s the part that surprises people most: insulin resistance happens in lean women too. Insulin resistance means your body needs to produce more and more insulin to keep blood sugar in range - and chronically high insulin nudges the ovaries to make more androgens. In lean PMOS it’s often subtler and easier to miss, because the screening tests doctors reach for first - fasting glucose, sometimes HbA1c - can look completely normal while the insulin system works overtime in the background.
Why this matters: a “normal” fasting glucose in a lean woman is often treated as the end of the metabolic conversation. For PMOS, it shouldn’t be. An oral glucose tolerance test (OGTT), ideally with insulin levels measured alongside, tells a far more honest story.
The cost of being dismissed
When lean women get told they “don’t look the type,” several things happen. The diagnosis gets delayed, sometimes by years. Metabolic screening gets skipped, because the assumption is that thin means metabolically fine. Symptoms like acne, hair thinning, or irregular cycles get treated cosmetically, one at a time, without anyone connecting them. And the standard advice - “just lose some weight” - lands somewhere between useless and absurd when there’s no weight to lose.
None of that is a reflection of how real your condition is. It’s a reflection of how strongly one body type came to dominate the picture of it.
What good care looks like for lean PMOS
The workup for lean PMOS is the same thorough workup every woman with this condition deserves - androgens measured properly (free testosterone, SHBG), ovulation actually assessed rather than assumed, metabolic health tested with an OGTT rather than fasting glucose alone, and a phenotype identified so treatment matches your version of the condition. What changes is mainly the emphasis: in lean presentations, cycle regulation and androgen symptoms often take centre stage, and metabolic issues need actively looking for, because nobody spots them by eye.
If your gut says something hormonal is going on and you keep hearing “you look fine” - your gut deserves a proper hearing. A specialist looking at your actual labs, rather than your appearance, is the fastest way to get one.