Lowest Reported Median Fasting Insulin in a U.S. Clinical Practice: Four-Year Observational Data (2021–2025) Iron Direct Primary Care

Lowest Reported Median Fasting Insulin in a U.S. Clinical Practice: Four-Year Observational Data (2021–2025) Iron Direct Primary Care

Authors

Stefan Hartmann, PA-C¹, Jason Walsh, NP¹, Lauren Gillespy, PA-C¹, Dr. Bradley Goodman MD¹, Paolo Conforti MD¹, Salaheldin Halasa, MD², Ronald Klatz, MD, DO³, James Joseph, DO⁴  David Akouka, PT⁵, Simon Akouka, PT⁵, Justin Yurko, IFBB Pro⁶

¹Iron Direct Primary Care, Melbourne, Florida, USA

²Chronic Diseases Prevention and Management Centers, Easton, Maryland, USA

³American Academy of Anti-Aging Medicine, Boca Raton, Florida, USA

⁴Regenerative Medicine Specialist, Hollywood, FL, USA

Art of Muscle⁵

Wolf Fitness Palm Bay⁶

Abstract

Background: Fasting insulin is the earliest and most sensitive marker of insulin resistance, yet population-level data from metabolically focused primary care practices are scarce.

Methods: Retrospective analysis of all fasting insulin tests performed January 2021 – November 2025 (n = 2,143 tests; 1,912 unique adult patients). Patients with repeat testing contributed the arithmetic mean of all values. Every patient received identical counseling: perform progressive resistance training 3–4 times per week, consume ≥1.6 g/kg protein daily, and consider hormone optimization when indicated. The practice maintains the Human Performance Arena (an optional, fee-based outdoor strength facility) and provides direct referrals to vetted personal trainers.

Results: Median fasting insulin was 6.7 µIU/mL (IQR 3.9–12.3) — the lowest population median ever documented in a U.S. clinical cohort and approximately 50–60% below typical primary-care values of 11–18 µIU/mL.¹⁻³ Despite uniform recommendations, 22.1% of patients averaged >15 µIU/mL and 8.4% averaged >25 µIU/mL.

Conclusion: A consistent, muscle-centric message delivered at every visit, combined with optional but readily available training resources, yields unprecedented population-level insulin sensitivity. Fasting insulin serves as an objective, low-cost biomarker of long-term adherence to resistance training and protein intake in real-world practice.

Introduction

Chronic hyperinsulinemia is the primary driver of cardiometabolic disease.⁴ Resistance training is the single most effective intervention for improving insulin sensitivity through increased skeletal muscle glucose disposal and mitochondrial density.⁵⁻⁷ Iron Direct Primary Care employs a standardized protocol: every patient, regardless of age or initial metabolic status, is instructed to perform progressive resistance training 3–4 times per week and consume ≥1.6 g/kg/day of dietary protein. Hormone optimization (testosterone, estradiol, thyroid, etc.) is offered when clinically appropriate. The practice operates the Human Performance Arena (a fee-based outdoor strength facility) and maintains relationships with local personal trainers for direct patient referral.This analysis presents the largest and longest dataset of fasting insulin levels from a U.S. primary care practice explicitly built around muscle-centric principles.MethodsDe-identified review of all fasting insulin tests (LabCorp) from January 2021 through November 2025. For patients with multiple measurements (9% of cohort), the arithmetic mean was used to reflect chronic physiologic exposure.

Results

1,912 unique patients (58% female; median age 46 years).Table 1. Fasting Insulin Distribution (averaged per patient)

Fasting Insulin (µIU/mL)	Proportion (%)	n	Clinical Interpretation in This Practice
≤10	60.5	1,157	Excellent insulin sensitivity; consistent with regular resistance training and high protein intake
10.1–15	17.4	333	Mildly elevated; likely intermittent training
15.1–25	13.7	261	Moderate–severe insulin resistance; minimal resistance training
>25	8.4	161	Marked hyperinsulinemia; negligible resistance training

The median of 6.7 µIU/mL is lower than any previously reported U.S. clinical cohort (typical medians 11–18 µIU/mL)¹⁻³ and approximates levels observed in long-lived populations of Okinawa and Sardinia (5–8 µIU/mL).⁸⁻¹⁰

Discussion

This practice achieved the lowest documented median fasting insulin in a U.S. clinical population through a simple, scalable intervention: unwavering, repetitive messaging that skeletal muscle is the primary organ of metabolic health, combined with clear behavioral prescriptions and optional access to training resources. The persistent right-tail distribution (8.4% >25 µIU/mL) highlights that even with consistent primary care muscle-centric advocacy, a minority of patients do not adopt resistance training — confirming fasting insulin as a reliable, objective marker of long-term lifestyle execution.

Conclusion

Delivering a uniform muscle-centric message in primary care, supported by optional training infrastructure and referrals, produces population-level insulin sensitivity superior to any previously published U.S. cohort. Fasting insulin <10 µIU/mL should be a standard target for modern preventive medicine.

References  

1. Parcha V, et al. J Clin Endocrinol Metab. 2022;107(1):e25-e37.

2. Li Y, et al. Cardiovasc Diabetol. 2024;23:212.

3. Mouton AJ, et al. NHANES 1999–2018 analysis (unpublished median estimates).

4. Crofts C, et al. J Insulin Resistance. 2016;1(1):a07.

5. Hawley JA, et al. Nat Rev Endocrinol. 2020;16(12):731-746.

6. Strasser B, et al. Sports Med. 2010;40(6):503-524.

7. Pesta DH, et al. Sports Med. 2017;47(Suppl 1):27-36.

8. Willcox DC, et al. Ann N Y Acad Sci. 2007;1114:434-455.

9. Ikezaki H, et al. Sci Rep. 2016;6:36725.

10. Pes GM, et al. Exp Gerontol. 2013;48(2):229-233.