Insulin, Fasting

PREP: Fast 10–14 hours (water only). The functional medicine community is stricter than standard guidance — they recommend a true 12-hour overnight fast for the most accurate baseline. Avoid vigorous exercise 24 hours before, as it can temporarily improve insulin sensitivity and lower fasting insulin. Do not consume caffeine before the draw. The functional medicine community considers optimal fasting insulin to be 2–5 µIU/mL, much tighter than the standard lab range (often 2.6–24.9). A fasting insulin above 8–10 is considered early insulin resistance by many functional practitioners, even if glucose and HbA1c look normal. Always pair with fasting glucose for HOMA-IR calculation.

Reflects common practices in thyroid, BHRT, and functional medicine communities. This may differ from standard clinical guidelines. Not medical advice — always discuss with your provider.