Fasting Insulin
How much insulin your pancreas is producing in the fasted state to keep blood glucose normal.
The earliest warning sign of metabolic dysfunction — frequently elevated 5–10+ years before fasting glucose or HbA1c drift out of range. If you run one metabolic marker beyond glucose, run this.
The plan of attack
In this order. Most people start at step four, which is why they change five things at once and learn nothing.
- Confirm the number is real
Haemolysis (burst red cells). Red cells rupturing in the tube spill their contents into the serum. Potassium, LDH, AST and magnesium are far higher inside cells than outside, so a haemolysed sample reports them falsely high. Caused by a difficult draw, a narrow needle, or shaking the tube. The lab usually flags it. If your result is odd and the report mentions haemolysis, that is your answer — repeat the draw. - Read it with its partner
Fast 9–12h. This is the marker that catches problems while they're still fully reversible. Draw it alongside: HbA1c (Hemoglobin A1c), Comprehensive Metabolic Panel (CMP), SHBG (Sex Hormone-Binding Globulin). - Work out which direction is yours
If it's high — Insulin resistance. Drives fat storage, inflammation, low SHBG, high triglycerides, and eventually type 2 diabetes. - Fix it in this order
Nutrition. Fat loss — especially visceral — is the dominant lever. Reduce refined carbohydrate and added sugar, prioritize protein and fiber, and consider carbohydrate timing around training. A 10-minute walk after meals measurably blunts glucose and insulin excursions.
Lifestyle. Resistance training builds the glucose sink — muscle is the primary disposal site. Add zone-2 cardio, post-meal walks, and fix sleep: even one night of poor sleep measurably worsens insulin sensitivity.
Supplements. Berberine (comparable to metformin in some trials), myo-inositol (particularly strong evidence in PCOS), magnesium, chromium, alpha-lipoic acid, and adequate vitamin D.
Hormones. Metformin and GLP-1 receptor agonists (semaglutide, tirzepatide, retatrutide) substantially improve insulin sensitivity. Correct low testosterone in men and treat PCOS in women — both feed the cycle.
Compounds. Anyone running MK-677 must track fasting insulin and HbA1c — GH-axis stimulation reliably degrades insulin sensitivity. GLP-1s dramatically improve it. Use with fasting glucose to calculate HOMA-IR = (glucose × insulin) / 405; optimal is under 1.5.
Work down the list, not across it. Adding a compound on top of an unfixed diet is why generic protocols fail. - Retest
Every 3–6 months, or 8–12 weeks after an intervention. Change one thing at a time, or the retest can't tell you which thing worked.
How to fix it
📚 Matthews DR et al., Diabetologia 1985 — HOMA-IR. Crofts C et al., Diabesity 2016 — hyperinsulinemia precedes dysglycemia.
🩸 Test your Fasting Insulin
Order directly through Marek Diagnostics — no doctor's visit needed, drawn at any Quest location in the US. Code CAMERON applies 10% off automatically.
Order this test — 10% off → Browse all 102 markers →What Fasting Insulin is usually tested alongside
On its own, one marker is a data point. These panels include Fasting Insulin plus the markers that make it interpretable — each names every test, why it is on the list, and loads the whole set into your cart in one click at 10% off.
includes this + 7 more markers — Weight that won't shift, energy crashes after meals, expanding waistline, family history of diabetes, or a fasting glucose that's crept into the 90s.
includes this + 8 more markers — Anyone over 30, anyone with a family history of early heart disease, or anyone who's been told their cholesterol is 'fine' and wants to know what that actually means.
includes this + 9 more markers · built for women — Irregular or absent periods, acne, unwanted hair growth, scalp thinning, difficulty losing weight, or you've been told 'probably PCOS' without a workup.
What moves your Fasting Insulin
14 compounds in the Vault have a documented effect on this marker, or are a reason to have measured it first:
Browse all 237 compounds & 350 supplements →
Would you feel it? Symptoms Fasting Insulin helps explain
People rarely search for a marker — they search for how they feel. These are the complaints where this marker is worth checking, and whether it is a first-line test or a follow-up once the obvious causes are ruled out.
Why your Fasting Insulin might be wrong
Most abnormal results are interference, not disease. These are the things that measurably move this specific marker — check them before you change anything. Each one says whether the number is wrong and should be repeated, badly timed and should be redrawn, or real with a cause worth explaining.
Rises after eating, so a non-fasted draw measures your breakfast rather than your baseline.
Draw fasted, 10–12 hours, water only.
Insulin responds within minutes to eating. Even a coffee with milk the morning of the draw will move it, and it is far more sensitive to this than glucose.
12 hours fasted, water only. This marker is unusually unforgiving.
Red cells rupturing in the tube spill their contents into the serum. Potassium, LDH, AST and magnesium are far higher inside cells than outside, so a haemolysed sample reports them falsely high. Caused by a difficult draw, a narrow needle, or shaking the tube.
The lab usually flags it. If your result is odd and the report mentions haemolysis, that is your answer — repeat the draw.
Improves insulin sensitivity acutely for up to 48 hours, so a draw the morning after training flatters the number.
Consistent conditions matter more than good ones — same routine every retest.
What Fasting Insulin means in combination
A single marker tells you a little. Combinations tell you the story — these are the named patterns this marker takes part in, and what each one points at.
The classic polycystic ovary syndrome pattern, with insulin resistance as the usual engine driving androgen excess.
Treating the insulin resistance often improves everything downstream — cycles, acne, hair. Myo-inositol has strong evidence; also fat loss, resistance training, and metformin or GLP-1 where appropriate. Work with a provider.
Classic compensated insulin resistance. Your pancreas is working overtime to keep glucose normal — so the standard screening tests look fine while the underlying problem builds.
This is the most reversible stage. Fat loss, resistance training, post-meal walks, fiber, reduced refined carbohydrate. Consider berberine or inositol; metformin/GLP-1 if clinically appropriate.
Insulin resistance reduces uric acid excretion by the kidney. So a raised urate is very often a metabolic signal arriving before anyone has a painful toe.
Treat the insulin resistance and urate usually follows. Cut fructose and alcohol (beer especially). Do not start urate-lowering drugs off one reading — that is a clinical decision with its own trade-offs.
C-peptide confirms the pancreas is still producing well, so this is a receptor-side problem rather than a production one. That distinction changes what actually helps.
Everything that improves insulin sensitivity applies and is likely to work: resistance training, fat loss, sleep, fibre, post-meal walking. A genuinely low C-peptide is the opposite situation and needs a clinician promptly.
What to test next
Markers rarely answer alone. These are the ones that put Fasting Insulin in context — each with its own full breakdown.
Frequently asked questions
2.6–24.9 µIU/mL — a range so wide it's nearly useless, because it includes many people with significant insulin resistance Ranges vary by laboratory and assay — always compare to the range printed on your own report.
<8 µIU/mL; <5 µIU/mL is excellent. The clearest example in all of bloodwork that 'in range' ≠ healthy.
Insulin resistance. Drives fat storage, inflammation, low SHBG, high triglycerides, and eventually type 2 diabetes.
Favorable when glucose is normal. Low insulin with high glucose suggests inadequate insulin production (type 1/late type 2) — that's a medical evaluation.
You can order Fasting Insulin directly through Marek Diagnostics without a doctor's visit — drawn at any Quest Diagnostics location in the US. Code CAMERON applies 10% off automatically.