Capacity 01 · Regulate Energy
Signal · Fasting Insulin
The hormonal cost of keeping blood sugar normal.
A1c tells you what glucose is doing. Fasting insulin tells you what it cost to get there. You can have a "normal" fasting glucose only because your pancreas is working overtime to hold the line — and that strain shows up in insulin long before it shows up anywhere else.
The ranges that matter
The earliest line to cross.
Lab "normal" often runs up to 25 µIU/mL. That is a diagnostic ceiling, not a health target. Metabolically healthy people sit in the single digits.
Fit / Optimal
≤ 6 µIU/mL
The body maintains fasting glucose without a lot of hormonal effort. Insulin sensitivity is preserved.
Well
6 – 15 µIU/mL
Starting to drift. Still inside lab "normal" — but the body is beginning to work harder than it should.
Sick / At Risk
> 15 µIU/mL (severe > 25)
Insulin resistance is developing. A1c may still look fine for years while this quietly climbs.
What it reveals
Insulin is the volume knob.
Insulin's job is to move glucose out of the bloodstream and into cells. When cells stop responding — the first sign of insulin resistance — the pancreas compensates by producing more. Blood sugar stays in range, but the price has gone up.
This is why a person can have a perfectly normal A1c and a perfectly normal fasting glucose and still be metabolically compromised. The system is still producing the right output. It's just costing more hormonally to do it. You only see that cost if you measure the hormone.
Fasting insulin is the earliest lab marker to move when the Regulate Energy capacity begins to strain. Years before A1c drifts upward, insulin is already climbing. That lead time is what makes it one of the most valuable coaching signals you can have.
What to look for
Rising fasting insulin with flat A1c means the body is compensating. Falling fasting insulin during a nutrition intervention — even with no weight change — means insulin sensitivity is recovering. That's often the first thing to move, and it's the most important thing to see move.
What moves it
Reduce the load. Rebuild the signal.
First levers
- Reduce the glycemic load at each meal — less refined starch, less liquid sugar.
- Anchor protein. Protein lowers insulin response per gram of food compared to refined carbs.
- Stop constant snacking. Insulin needs time between meals to fall.
- Reduce visible and hidden added sugar exposure across the day.
Second levers
- Strength train. Muscle is the largest glucose sink — bigger sink, lower insulin.
- Zone 2 aerobic work — 2–4 sessions per week — restores mitochondrial flexibility.
- Protect sleep. Insulin sensitivity moves night-over-night with sleep quality.
- Consider a consistent eating window (10–12 hours) so the body actually fasts.
Why it sits with "Regulate Energy"
Fasting insulin is the earliest of the four Regulate Energy markers.
HbA1c confirms what's happening to glucose,
TG:HDL shows the downstream fuel traffic, and
ApoB shows the cardiovascular consequence. Together they describe how cleanly fuel is being handled.
Go deeper
Coaching and education only. Not medical diagnosis or treatment.