Free Androgen Index (FAI)

The Free Androgen Index (FAI) measures the ratio of total testosterone (TT) to sex hormone-binding globulin (SHBG) and reflects how much biologically active (free) testosterone is circulating in the body. Unlike total testosterone alone, the FAI provides a clearer picture of androgen activity — especially in women, where even small hormonal shifts can influence mood, metabolism, and reproductive health. The FAI is particularly valuable in assessing androgen excess conditions like polycystic ovary syndrome (PCOS), as well as metabolic and cardiovascular risk.

Androgens like testosterone play essential roles in energy, muscle tone, libido, and mood. However, both too much and too little free androgen activity can disrupt health.

• Elevated FAI is often linked to PCOS, insulin resistance, and metabolic syndrome, increasing long-term risks of cardiovascular disease and type 2 diabetes.

• Low FAI, on the other hand, may contribute to fatigue, low libido, and loss of lean muscle, particularly in women using oral contraceptives or experiencing perimenopause.

• Because SHBG fluctuates with metabolic health, liver function, and oestrogen levels, FAI also acts as a metabolic health barometer, not just a hormone marker.

FAI can shift for several physiological and lifestyle reasons:

• Menstrual Cycle: Testosterone and SHBG levels naturally vary during the cycle, influencing FAI.
  

• Age & Menopause: FAI tends to rise with age as SHBG declines, especially after menopause.
  

• Body Composition: Higher body fat and insulin resistance reduce SHBG, raising FAI.
  

• Medications: Oral contraceptives or estrogen therapy increase SHBG, lowering FAI; anabolic steroids or insulin-sensitizing drugs can reduce it.
  

• Liver or Thyroid Health: Since SHBG is produced in the liver and regulated by thyroid hormones, dysfunction in either can shift FAI levels.
  

If Your FAI Is High:

Address Insulin Resistance: Prioritize blood sugar balance through a low-glycemic, whole-food diet rich in fiber, protein, and omega-3 fats. Avoid refined carbohydrates and excess sugar.

Reduce Androgen Excess Naturally:

• Exercise regularly — resistance and aerobic training improve insulin sensitivity and lower androgens.

• Support liver detoxification with cruciferous vegetables (broccoli, cauliflower, kale) to aid hormone metabolism.
  

Medical Support:

• Speak with your clinician about testing for PCOS or adrenal overactivity.

• In some cases, oral contraceptives, metformin, or anti-androgens (e.g., spironolactone) may be used to regulate hormones.
  

Lower Stress: Chronic stress elevates cortisol, which can indirectly increase androgen production — mindfulness, sleep, and nervous system regulation help balance both.

If Your FAI Is Low:

Assess SHBG and Estrogen Levels: Elevated SHBG (often from oral contraceptives or high estrogen) can lower free androgens. Discuss with your practitioner if this balance needs adjustment.

Support Hormone Production:

• Include healthy fats and cholesterol (eggs, olive oil, avocado, wild-caught fish) to provide building blocks for steroid hormones.

• Ensure adequate zinc, magnesium, and vitamin D, which support androgen synthesis.
  

Address Adrenal or Pituitary Health: Chronic fatigue, low libido, and low mood may signal adrenal or pituitary insufficiency; consider cortisol and DHEA testing.

Review Medications: Oral contraceptives and estrogen therapies can suppress FAI; your clinician can help explore alternatives if symptoms persist.

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2. Zhao, W., Li, Z., Cai, B., Zhou, C., & Mai, Q. (2024). Impact of dehydroepiandrosterone sulfate and free androgen index on pregnancy and neonatal outcomes in PCOS patients. Reproductive Biology and Endocrinology, 22(1), 43. https://doi.org/10.1186/s12958-024-01212-y

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6. Rahmatnezhad, L., Moghaddam-Banaem, L., & Behrouzi Lak, T. (2023). Free androgen index relations with oxidative stress and insulin resistance in PCOS. Scientific Reports, 13(1), 5118. https://doi.org/10.1038/s41598-023-31406-0

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