Lean PCOS is a type of PCOS that does not involve overweight or obesity. Because of differences in body composition in the types of PCOS, lean PCOS may need different treatment approaches.

Polycystic ovary syndrome (PCOS) is a complex metabolic endocrine condition that affects 1 in 10 adult females. It can cause a diverse range of features, including an irregular menstrual cycle, an excess amount of androgens (a predominantly male sex hormone), and physical features such as cysts that may show up on an ultrasound.

PCOS can cause various symptoms depending on an individual’s body weight. There are two types of PCOS: overweight or obese PCOS and lean PCOS.

This article explains lean PCOS, including symptoms, diagnosis, and treatment.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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PCOS typically occurs in people who have obesity or overweight. However, it can affect people with a body mass index (BMI) of 25 or less. The “healthy weight” BMI range recommended by the Centers for Disease Control and Prevention (CDC) is 18.5–24.9.

Lean PCOS differs from overweight or obese PCOS in body composition and other factors. This means that doctors need to tailor treatment options to the individual needs of a person with lean PCOS.

Most occurrences of PCOS involve at least one of the following characteristics:

People with obese or lean PCOS typically have similar metabolic profiles, as there are similar levels of visceral adipose tissue (body fat), which is a hormonal feature of body fat that affects processes within the body.

Other characteristics that apply to both lean and obese PCOS are low grade inflammation and oxidative stress. Oxidative stress is an imbalance of free radicals and antioxidants in the body.

However, characteristics of lean PCOS can differ from those of obese PCOS in body composition and other factors, such as hormonal profiles.

Insulin resistance is when cells within the body do not respond to insulin, so the tissues do not use insulin correctly during glucose metabolism. Insulin resistance can occur in either form of PCOS. Even if body fat levels are low, people with PCOS can have high blood insulin and insulin resistance.

However, rates of insulin resistance are lower in people with lean PCOS, with one study showing insulin resistance to affect 83.3% of participants with lean PCOS compared with 93.1% of participants with overweight or obesity.

Research in this area is ongoing, as it is still unclear whether insulin resistance affects people with lean PCOS to the same degree as those with overweight or obese PCOS.

Symptoms of PCOS may include:

People with lean PCOS are particularly likely to experience symptoms similar to ones that affect females during puberty, such as acne, irregular periods, and depression.

PCOS can present in a range of ways that overlap with the signs and symptoms of other conditions. Because of this, the criteria for identifying PCOS often relies on a diagnosis of exclusion, which means ruling out other potential conditions such as Cushing syndrome or thyroid disorders.

Lean PCOS can be more challenging to diagnose than overweight or obese PCOS, as there are typically fewer main symptoms present.

Lifestyle changes, such as increasing nutritional intake, can help ease insulin resistance, infertility, and cardiometabolic disorders. People with lean PCOS may not need to lose weight but should aim to maintain a moderate weight.

Staying physically active and consuming a nutrient-dense diet can help improve androgen levels and decrease insulin resistance. In some cases, this can reverse lean PCOS completely.

Other aspects of treatment include:

The following are some questions people frequently ask about lean PCOS.

How rare is lean PCOS?

Around 80% of PCOS diagnoses are overweight or obese, so lean PCOS only accounts for approximately 20%.

What are the four types of PCOS?

There are several methods for classifying PCOS. One four-part approach uses phenotypes, or characteristics, to classify PCOS in the following categories:

  • Phenotype A or full-blown syndrome PCOS: This typically involves hyperandrogenism, ovulatory dysfunction, and polycystic ovaries.
  • Phenotype B or non-PCO PCOS: This typically involves hyperandrogenism and ovulatory dysfunction.
  • Phenotype C or ovulatory PCOS: This typically involves hyperandrogenism and polycystic ovaries.
  • Phenotype D or non-hyperandrogenic PCOS: This typically involves ovulatory dysfunction and polycystic ovaries.

Is lean PCOS a risk factor for diabetes?

Yes, but the prevalence of diabetes is lower in people with lean PCOS.

PCOS is a condition that involves an imbalance of reproductive hormones. It can present in various ways. However, a key component of PCOS is insulin resistance, which is likely to cause hormonal and metabolic symptoms.

Presentations of PCOS can be obese or overweight, or lean. Lean PCOS is much less common and more challenging to diagnose, as there are generally fewer of the typical symptoms that occur with PCOS.

Treatment for lean PCOS involves maintaining a moderate weight, staying physically active, and following a nutritious and balanced diet. This can help ease insulin resistance and reduce androgen levels.

An individual with lean PCOS should speak with a healthcare professional about the most effective ways to manage the condition.