What blood tests show metabolic health?

The standard set is fasting glucose, hemoglobin A1c, triglycerides and HDL cholesterol, plus two measurements taken in the clinic: blood pressure and waist circumference. Most are part of a routine checkup.

What is a normal fasting glucose and A1c?

The CDC lists a fasting blood sugar of 99 mg/dL or below and an A1c below 5.7% as normal. Results above those ranges should be discussed with a clinician, who may repeat the test.

How many Americans are metabolically healthy?

It depends on the definition. One NHANES analysis found 12.2% of adults met optimal levels for all five metabolic measures in 2009 to 2016. A broader cardiometabolic definition that also counted adiposity and heart disease found 6.8% in 2017 to 2018.

What is a good triglyceride-to-HDL ratio?

There is no official target. One study of overweight adults found a ratio of 3.0 or more (in mg/dL) identified people likely to be insulin resistant, but it had modest accuracy and was not tested in everyone.

Should I ask for a fasting insulin test?

Fasting insulin is not part of standard panels and lacks a universal reference range because assays differ. It can be combined with glucose to calculate HOMA-IR, which is mainly a research tool. Ask your clinician whether it would change anything for you.

What is metabolic syndrome?

Under the harmonized definition, it is having at least three of five findings: large waist, raised triglycerides, low HDL, raised blood pressure and raised fasting glucose. Only a clinician can diagnose it.

Metabolic Health Blood Tests: Which Markers to Check and What the Ranges Mean

Metabolic health is usually measured with five things: waist size, blood pressure, fasting glucose (often with A1c), triglycerides and HDL cholesterol. Most are part of a routine checkup. A 2019 national survey analysis found that only 12.2% of US adults had optimal levels of all of them without medication. This page lists the published cut-offs, explains a few extra markers, and is general information, not medical advice. It cannot tell you whether you have a condition; only a clinician can.

The core markers and their cut-offs

The table uses the NHLBI diagnosis page, the CDC’s testing ranges and the “optimal” cut-offs used in the Araújo NHANES analysis.

Marker	Healthy or optimal level	Level that counts toward metabolic syndrome
Waist circumference	Under 40 in (men), 35 in (women)	Over 40 in (men), 35 in (women); lower cut-offs for some ethnic groups
Blood pressure	Under 120/80 mmHg	Consistently 130/85 mmHg or higher
Fasting glucose	70 to 99 mg/dL	100 mg/dL or higher
Hemoglobin A1c	Below 5.7%	Not a syndrome criterion; 5.7% or higher is above the CDC normal range
Triglycerides	Under 150 mg/dL	Consistently over 150 mg/dL
HDL cholesterol	40 mg/dL or more (men), 50 or more (women); 60 or more is linked to lower heart risk	Under 40 mg/dL (men), 50 (women)

Two practical points. A fasting glucose test needs 8 to 12 hours without food, per NHLBI. And taking medication for blood sugar, blood pressure or lipids changes how results are interpreted, so a normal number on treatment is not the same as a normal number without it.

How the definitions fit together

The 2009 harmonized definition from several major health organizations agreed that three abnormal findings out of five qualify as metabolic syndrome, with no single required component. Waist cut-offs were left to national or regional standards because risk at a given waist size differs between populations.

“Optimal metabolic health” in research is a stricter idea: being in the healthy range on every marker, without medication. Two widely quoted numbers come from two different definitions:

Study	Definition	Share of US adults meeting it
Araújo 2019, 8,721 adults, 2009 to 2016	Optimal waist, glucose and A1c, blood pressure, triglycerides and HDL, no medication	12.2%
O’Hearn 2022, 55,081 adults, 1999 to 2018	Optimal adiposity, glucose, lipids and blood pressure, and no clinical cardiovascular disease	6.8% in 2017 to 2018

On the Huberman Lab episode, Casey Means listed the Araújo-style cut-offs (fasting glucose under 100, triglycerides under 150, A1c under 5.7%, blood pressure under 120/80) and then gave the 6.8% figure, which comes from the broader O’Hearn definition. She also said, “My ranges for optimal are tighter than these,” and that the markers are easy to change in one to two months with lifestyle habits. That is her view; neither survey tested how quickly markers change.

Extra markers worth understanding

Marker	What it adds	Caveat
Triglyceride-to-HDL ratio	In McLaughlin 2003, a ratio of 3.0 (mg/dL units) best identified insulin-resistant overweight adults	258 overweight adults only; sensitivity 64%, specificity 68%
Fasting insulin	Same study’s best cut-off was 109 pmol/L	Assays are not standardized, so ranges vary by lab
HOMA-IR	Combines fasting glucose and insulin into an insulin-resistance estimate; in the original 1985 paper it correlated 0.88 with the clamp method	Low precision for individuals (31% coefficient of variation)

Means also mentions apoB, uric acid, hs-CRP and liver tests as further options. They can be useful, but they are not part of the core definitions above, and whether to order them is a conversation for your clinician.

What moves these markers: the CALERIE trial

The best long-term test of whether eating less shifts these numbers in healthy people is CALERIE. In the 2-year trial, reported by William Kraus and colleagues, 218 young and middle-aged adults without obesity were assigned to a 25% calorie restriction target or their usual diet. They actually achieved an average cut of 11.9% and lost 7.5 kg, about 71% of it fat.

Marker	Change with calorie restriction vs control
LDL cholesterol	Significantly lower
Total cholesterol to HDL ratio	Significantly lower
Systolic and diastolic blood pressure	Significantly lower
C-reactive protein	Significantly lower
Insulin sensitivity	Significantly improved
Metabolic syndrome score	Significantly improved

The authors concluded that “2 years of moderate calorie restriction significantly reduced multiple cardiometabolic risk factors in young, non-obese adults.” The results held after accounting for how much weight people lost. These are changes in risk markers, not in heart attacks or lifespan, and the participants were already healthy and well supported by study staff. The rest of the weight lost, roughly 29%, was not fat, which is one reason trials and reviews pair any calorie cut with strength training and enough protein; see intermittent fasting and muscle loss for how that plays out with eating windows. If you change your diet, retest markers after a few months under the same conditions rather than after a few days.

Does the eating pattern matter as much as the amount? Trials comparing intermittent fasting with ordinary calorie restriction mostly find similar changes in weight, glucose and lipids when total intake is similar; see intermittent fasting vs calorie restriction. Whether better markers translate into a longer life is a separate question, covered in intermittent fasting and longevity.

Why fasting glucose gets attention

A 2021 Cell Metabolism study compared lifelong records from mice, monkeys and humans. Fasting glucose rose with age in humans and monkeys, and higher glucose was associated with higher mortality in both, while the opposite held in mice. It is an observational comparison and a reminder that animal findings on glucose do not always transfer to people.

How to use your results

Get the numbers, not just “normal”. Ask for your actual values from routine bloodwork, plus your waist and blood pressure; the NHLBI page explains each measurement.
Compare with the table to see which are in the healthy range.
Discuss anything outside it with a clinician, who may repeat a test before drawing conclusions.
Track changes over time under similar conditions, such as the same fasting length and time of day.

Daily habits linked to better short-term glucose control are covered in the blood glucose protocol, meal timing in the time-restricted eating guide, and aerobic training in Zone 2 cardio.