Arun Baby

ML Researcher → AI Engineer → Architecting intelligent agent systems

8 minute read

Labs define “normal” by what is common in the population they tested.

The US adult population is the most metabolically compromised in recorded history – with 88% having at least one marker of metabolic dysfunction. 1 Building reference ranges from this population produces normal ranges that include substantial metabolic disease.

A fasting insulin of 25 μIU/mL is normal by most lab standards. The biology suggests it should be below 8. The gap is where insulin resistance, visceral fat accumulation, and cardiovascular risk live – quietly, for years, inside the “normal” range.

TL;DR

Lab reference ranges are built from population averages, not from what the biology needs to function optimally. The gap between “normal” and “optimal” is where metabolic disease lives. These are the targets that matter and the levers that move them.

Blood glucose meter, insulin vial, and metabolic panel with rows circled in red pen on a clinical lab bench

I. Testosterone (Male)

Testosterone is the primary anabolic and vitality hormone in men. It drives muscle protein synthesis, libido, bone density, red blood cell production, cognitive function, and mood. Low testosterone is associated with higher all-cause mortality. 2

Lab reference ranges vs. optimal:

  • Lab “normal”: 300–1,000 ng/dL total
  • Functional medicine optimal: 700–900 ng/dL total
  • The bottom of the “normal” range includes the clinical definition of hypogonadism in some guidelines

Free testosterone: 5–25 ng/dL normal; free testosterone matters more than total because it is the biologically active fraction. Sex hormone-binding globulin (SHBG) binds testosterone and renders it unavailable – SHBG elevation drives low free T even when total T is adequate.

Natural optimization levers:

Sleep: Testosterone is secreted primarily during sleep, with the majority during deep slow-wave sleep. Restricting sleep from 8 to 5 hours reduces testosterone by 10–15% – equivalent to aging 10–15 years in hormonal terms. 3

Resistance training: Heavy compound movements acutely elevate testosterone. Chronic training raises baseline levels, particularly in men who are undertrained. Overtraining (insufficient recovery) suppresses it.

Body composition: Adipose tissue aromatizes testosterone to estrogen. Each 10% reduction in body fat percentage produces a measurable increase in free testosterone. Visceral fat is particularly aromatase-active.

Zinc: 30mg per day corrects testosterone suppression in zinc-deficient men. It does not raise testosterone in zinc-replete men – test first, supplement to correct deficiency. 4

Vitamin D3: Low 25-OHD (below 30 ng/mL) is consistently associated with lower testosterone. Supplementation corrects this in deficient individuals. 5

Cortisol: The primary natural testosterone suppressor. Cortisol directly inhibits Leydig cell function (the testicular cells that produce testosterone). Chronic psychological stress, sleep debt, and caloric restriction all suppress testosterone through this pathway.

II. Insulin Sensitivity

Insulin resistance is the central metabolic dysfunction underlying type 2 diabetes, PCOS, cardiovascular disease, non-alcoholic fatty liver disease, and a substantial fraction of obesity. It develops over years, mostly silently, within “normal” lab ranges.

Target markers:

  • Fasting insulin: <5–8 μIU/mL (most labs call 25 μIU/mL normal)
  • Fasting glucose: 70–90 mg/dL
  • HbA1c: <5.4%
  • HOMA-IR: <1.5 (calculated as fasting glucose × fasting insulin ÷ 405)

HOMA-IR catches insulin resistance years before fasting glucose does. The pancreas compensates for early insulin resistance by secreting more insulin, keeping glucose artificially normal. High insulin with normal glucose is already dysfunction.

The most effective insulin sensitivity interventions:

Zone 2 exercise: Each 45-minute session upregulates GLUT4 transporter expression for 24–48 hours – meaning cells take up glucose directly from the blood without needing insulin signaling. 6 This effect is dose-responsive and does not require weight loss to manifest.

Muscle mass: Each kilogram of muscle is insulin-sensitive glucose disposal capacity. Sarcopenic individuals (low muscle mass) have dramatically impaired glucose management independent of body fat. Building muscle is insulin resistance therapy.

Post-exercise carbohydrates: GLUT4 expression peaks in the 2 hours immediately post-exercise. Eating carbohydrates during this window minimizes the glucose and insulin spike for the same carbohydrate load. This is the optimal time for higher-carbohydrate meals.

Meal sequencing: Eating protein and fat before carbohydrates within the same meal reduces the postprandial glucose spike by 30–40%, independent of the total carbohydrate consumed. 7

III. Growth Hormone

Growth hormone drives cellular repair, fat oxidation, immune function, cognitive performance, and recovery. Unlike testosterone, it is not something to supplement for most people – it is something to protect.

The primary pulse: GH secretion is highly pulsatile, with the largest pulse occurring in the first 90 minutes of sleep, specifically during slow-wave sleep. 8 Anything that suppresses slow-wave sleep suppresses GH.

Natural GH amplifiers:

  • Deep slow-wave sleep (the primary driver)
  • Sauna: 2–5× GH elevation post-session 9
  • Fasting and caloric restriction
  • High-intensity exercise

Natural GH suppressors:

  • Insulin: GH is suppressed by elevated blood insulin. Carbohydrates before bed raise insulin, which suppresses the overnight GH pulse – one mechanism by which late eating impairs body composition and recovery
  • Alcohol: Suppresses slow-wave sleep and directly suppresses GH
  • Obesity: Excess visceral fat increases somatostatin (GH’s inhibitory hormone)

Practical implication: The 2–3 hour meal cutoff before sleep protects the overnight GH pulse. This is not primarily about digestion – it is about insulin clearance before the slow-wave sleep window.

IV. Metabolic Biomarker Targets

These are the numbers to know. Most are available from a standard blood panel; some require specific requests.

Marker Lab Normal Optimal Target
Fasting glucose 70–100 mg/dL 70–90 mg/dL
Fasting insulin <25 μIU/mL <5–8 μIU/mL
HbA1c <5.7% <5.4%
HOMA-IR Not routinely reported <1.5
Triglycerides <150 mg/dL <100 mg/dL
HDL cholesterol >40 mg/dL (M) >50 mg/dL
TG:HDL ratio Not routinely reported <2.0
hs-CRP <3 mg/L <1 mg/L
25-OHD (vitamin D) >20 ng/mL 40–60 ng/mL
Total testosterone (M) 300–1,000 ng/dL 700–900 ng/dL

The TG:HDL ratio (triglycerides divided by HDL) is one of the most underused single-number metabolic health indicators. A ratio above 3.5 in Caucasians and above 3.0 in other populations is strongly predictive of insulin resistance. Below 2.0 is the target. 10

The Metabolic Health Protocol

Fix sleep first (testosterone and GH depend on it). Add Zone 2 exercise (GLUT4, insulin sensitivity). Hit protein targets (muscle mass as glucose disposal). Reduce refined carbohydrates and alcohol (insulin, cortisol, GH suppression). Sequence meals: protein before carbohydrates. Stop eating 2–3 hours before sleep.

The same inputs drive all four hormone systems in the right direction simultaneously.

References

Medical disclaimer: This post is for informational purposes only and does not constitute medical advice. The protocols described here are based on published research and expert commentary, not clinical recommendations. Consult your physician before changing medications, supplements, exercise regimens, or any other health intervention. Individual circumstances vary — professional guidance matters.

FAQ

Should everyone get fasting insulin tested?

Yes, particularly anyone with family history of diabetes, elevated triglycerides, central adiposity, or fatigue after carbohydrate-heavy meals. Fasting glucose alone misses early insulin resistance for years while the pancreas compensates with higher output. Adding fasting insulin costs very little and catches metabolic dysfunction a decade earlier.

What is the fastest way to improve insulin sensitivity?

A single 45-minute Zone 2 cardio session raises GLUT4 expression within hours. Combined with eliminating refined carbohydrates, the improvement in fasting insulin is often measurable within 2–4 weeks. Muscle mass is the slower but more durable lever – each kg added improves insulin sensitivity persistently, not just for 24–48 hours post-exercise.

Is testosterone supplementation safe?

Physiological replacement (returning levels to the natural optimal range, not supraphysiological bodybuilding doses) has a strong safety profile in men with documented hypogonadism. The risks primarily emerge at supraphysiological doses or without monitoring. Any testosterone therapy should include monitoring of hematocrit, estradiol, and PSA, and be managed by a physician familiar with the research.

  1. Araújo, J., Cai, J., & Stevens, J. (2019). Prevalence of optimal metabolic health in American adults. Metabolic Syndrome and Related Disorders, 17(1), 46–52. ↩

  2. Khera, M., et al. (2014). A new era of testosterone and prostate cancer: from physiology to clinical implications. European Urology, 65(1), 115–123. ↩

  3. Leproult, R., & Van Cauter, E. (2011). Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA, 305(21), 2173–2174. ↩

  4. Prasad, A. S., et al. (1996). Zinc status and serum testosterone levels of healthy adults. Nutrition, 12(5), 344–348. ↩

  5. Pilz, S., et al. (2011). Effect of vitamin D supplementation on testosterone levels in men. Hormone and Metabolic Research, 43(3), 223–225. ↩

  6. Richter, E. A., & Hargreaves, M. (2013). Exercise, GLUT4, and skeletal muscle glucose uptake. Physiological Reviews, 93(3), 993–1017. ↩

  7. Shukla, A. P., et al. (2017). Food order has a significant impact on postprandial glucose and insulin levels. Diabetes Care, 38(7), e98–e99. ↩

  8. Van Cauter, E., et al. (2000). Sleep and the somatotropic axis. JAMA, 284(7), 861–868. ↩

  9. Laukkanen, T., et al. (2018). Cardiovascular and other health benefits of sauna bathing. Mayo Clinic Proceedings, 93(8), 1111–1121. ↩

  10. McLaughlin, T., et al. (2003). Use of metabolic markers to identify overweight individuals who are insulin resistant. Annals of Internal Medicine, 139(10), 802–809. ↩

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