A 2018 analysis published in Metabolic Syndrome and Related Disorders, led by Joana Araujo at the University of North Carolina, assessed metabolic health in 8,721 US adults using five clinical criteria: waist circumference, blood pressure, fasting glucose, triglycerides, and HDL cholesterol. The proportion meeting optimal thresholds on all five markers, without medication, was 12.2 percent. Almost 88 percent of American adults were metabolically unhealthy by at least one of these criteria. UK data, while using slightly different cut-offs, shows a similar picture. This is not a finding about obesity; approximately half of adults with normal BMI are metabolically unhealthy by these criteria. It is a finding about the downstream consequences of modern eating patterns, physical inactivity, chronic sleep restriction, and chronic stress, operating primarily through the mechanism of insulin resistance.
What Metabolic Health Actually Means
Metabolic health describes the efficiency with which the body manages energy at a cellular level: how responsive cells are to insulin signalling, how well the body handles glucose loads, how efficiently it oxidises fat, and how well it maintains the hormonal and inflammatory environment required for normal cellular function. The central mediator is insulin sensitivity: the degree to which cells, particularly muscle, liver, and fat cells, respond appropriately to insulin signals to take up glucose, suppress fat release, and initiate protein synthesis. When insulin sensitivity is impaired, insulin resistance develops: the pancreas compensates by secreting more insulin, blood insulin levels rise, and a cascade of secondary effects follows: elevated blood pressure, elevated triglycerides, reduced HDL, increased visceral fat deposition, and elevated fasting and post-meal blood glucose.
The clinical significance of insulin resistance extends far beyond blood sugar. Hyperinsulinaemia, chronically elevated insulin from compensatory secretion, is independently associated with cancer risk across multiple sites through insulin-like growth factor signalling pathways that promote cell proliferation and inhibit apoptosis. Insulin resistance in the brain impairs glucose uptake in neurons, contributing to the bioenergetic deficits that precede Alzheimer's disease pathology, leading some researchers to describe Alzheimer's as type 3 diabetes. Insulin resistance in the kidney promotes sodium and water retention, contributing to hypertension. The metabolic syndrome picture, which is the clinical presentation of established insulin resistance, is associated with two to four times the risk of cardiovascular disease, three times the risk of type 2 diabetes, and elevated risk of dementia, several cancers, NAFLD, polycystic ovary syndrome, and gout.
The Primary Drivers of Metabolic Dysfunction
The primary dietary driver of insulin resistance is excess caloric intake, particularly excess intake of refined carbohydrates and fructose, which produce hepatic fat accumulation and liver insulin resistance that precedes and drives peripheral insulin resistance. Ultra-processed foods, which now account for approximately 57 percent of caloric intake in UK adults, are the dominant source of these excess refined carbohydrates and also contain additives, emulsifiers, and artificial flavours that independently promote gut permeability and inflammation. Physical inactivity is the second major driver: skeletal muscle is the primary site of insulin-stimulated glucose disposal, and in the absence of muscular demand, this capacity declines progressively.
Sleep restriction is a frequently overlooked but potent driver of insulin resistance. A study in the Annals of Internal Medicine found that restricting sleep to 5.5 hours per night for two weeks reduced insulin sensitivity by 25 percent compared with the same dietary conditions with 8.5 hours of sleep. The mechanisms include elevated cortisol from sleep restriction, which promotes gluconeogenesis and adipose tissue lipolysis, increasing circulating free fatty acids that drive muscle insulin resistance. Chronic psychological stress produces similar effects through sustained cortisol elevation. Visceral adiposity both results from and exacerbates insulin resistance through the release of free fatty acids and pro-inflammatory cytokines.
Restoring Metabolic Health: The Evidence-Based Programme
Restoring insulin sensitivity is achievable through lifestyle intervention and does not require pharmacological management in the majority of adults who are not yet at the point of type 2 diabetes. The interventions with the strongest evidence are: resistance and aerobic exercise combined, which increases GLUT4 transporter expression in muscle, improving insulin-independent glucose uptake; weight loss, particularly visceral fat reduction, which directly reduces the hepatic fat and inflammatory cytokine environment that drives insulin resistance; reduced refined carbohydrate intake, which lowers the glycaemic load that repeatedly challenges pancreatic function; improved sleep, which restores normal cortisol patterns and gluconeogenesis regulation; and stress management, which reduces chronic cortisol elevation.
At Zhen Wellness on the Isle of Man, metabolic health assessment includes fasting glucose, fasting insulin, HbA1c, triglycerides, HDL cholesterol, blood pressure, and waist circumference at minimum. The HOMA-IR calculation from fasting glucose and insulin identifies insulin resistance before it appears in fasting glucose or HbA1c, providing an earlier intervention window. Many adults presenting to the Longevity MOT at Zhen Wellness discover that their metabolic health is significantly worse than their standard GP blood tests suggest; the standard NHS panel does not include fasting insulin or HOMA-IR, missing the early and intermediate stages of insulin resistance that precede elevated glucose by ten to twenty years.
- Only 12 percent of adults are metabolically healthy by evidence-based criteria; 88 percent are unhealthy on at least one marker
- Insulin resistance drives hypertension, dyslipidaemia, visceral obesity, type 2 diabetes, Alzheimer's, multiple cancers, and NAFLD
- Ultra-processed foods account for 57 percent of UK caloric intake and are a primary driver of insulin resistance and gut dysfunction
- Sleep restriction to 5.5 hours reduces insulin sensitivity by 25 percent within two weeks regardless of dietary quality
- Resistance training increases GLUT4 expression in muscle, improving insulin-independent glucose disposal
- HOMA-IR from fasting insulin and glucose identifies insulin resistance 10 to 20 years before it appears in fasting glucose
- The combination of resistance exercise, reduced refined carbohydrate, adequate sleep, and visceral fat loss restores metabolic health without medication in most pre-diabetic adults
Sources
- Araujo, J., Cai, J., & Stevens, J. (2019). Prevalence of optimal metabolic health in American adults. Metabolic Syndrome and Related Disorders, 17(1), 46-52.
- Nedeltcheva, A.V., et al. (2010). Insufficient sleep undermines dietary efforts to reduce adiposity. Annals of Internal Medicine, 153(7), 435-441.
- DeFronzo, R.A., & Tripathy, D. (2009). Skeletal muscle insulin resistance is the primary defect in type 2 diabetes. Diabetes Care, 32(Suppl 2), S157-S163.
- De la Monte, S.M., & Wands, J.R. (2008). Alzheimer's disease is type 3 diabetes: evidence reviewed. Journal of Diabetes Science and Technology, 2(6), 1101-1113.
- van der Klaauw, A.A., & Farooqi, I.S. (2015). The hunger genes: pathways to obesity. Cell, 161(1), 119-132.