Insulin resistance

What it is

Insulin resistance is a metabolic condition affecting an estimated 30–40% of adults in Western countries, in which the body's cells — particularly in the liver, skeletal muscle, and adipose tissue — fail to respond normally to insulin, forcing the pancreas to produce progressively more of the hormone to maintain blood glucose control. Also called impaired insulin sensitivity, insulin resistance is the central metabolic defect underlying type 2 diabetes, polycystic ovary syndrome (PCOS), metabolic syndrome, non-alcoholic fatty liver disease (NAFLD), and a significant share of cardiovascular disease risk.

Insulin is a peptide hormone secreted by the pancreatic beta cells. Under normal conditions it acts as a molecular key, binding to cell-surface receptors and triggering glucose uptake from the bloodstream. When that signalling pathway is impaired, the pancreas compensates by secreting more insulin — a state called hyperinsulinaemia. Chronically elevated insulin has consequences well beyond blood sugar: it amplifies androgen production in the ovaries, suppresses sex hormone-binding globulin (SHBG), promotes visceral fat accumulation, and drives systemic inflammation.

In Canada, Diabetes Canada estimates that roughly 5.7 million Canadians are living with prediabetes — the stage at which insulin resistance has already begun to impair glucose regulation — and the majority are unaware of it. Identifying insulin resistance before it progresses to type 2 diabetes represents one of the most actionable preventive windows in primary care.

Causes and mechanism

Insulin resistance develops from an interplay of genetic susceptibility and modifiable lifestyle and hormonal factors.

Adiposity and inflammation. Visceral fat — the fat stored deep in the abdomen around the organs — releases pro-inflammatory cytokines and free fatty acids that directly impair insulin receptor signalling in muscle and liver cells. Even modest excess visceral fat can initiate this process.

Physical inactivity. Skeletal muscle accounts for the majority of post-meal glucose disposal. Reduced muscle mass or activity substantially lowers the body's capacity to respond to insulin.

Hormonal contributors. Several hormonal states worsen insulin sensitivity:

Hormonal factor	Mechanism
Cortisol excess (chronic stress, Cushing's)	Promotes hepatic glucose output; inhibits insulin-mediated uptake in muscle and fat
Hypothyroidism	Slows glucose metabolism; reduces GLUT4 transporter expression
PCOS	Insulin resistance is both a feature and a driver of excess ovarian androgen production
Growth hormone deficiency	Associated with increased visceral fat and reduced insulin sensitivity

Other contributors include high-glycaemic and ultra-processed diets, smoking, inadequate sleep (even two to three nights of poor sleep measurably impairs insulin sensitivity), and certain medications — notably corticosteroids, atypical antipsychotics, and some antiretrovirals.

Symptoms and diagnosis

Insulin resistance is often clinically silent for years. When signs do appear, they may include:

• Acanthosis nigricans — dark, velvety skin patches in body folds (neck, armpits, groin), caused directly by elevated insulin stimulating keratinocyte proliferation
• Central weight gain and difficulty losing weight despite dietary effort
• Post-meal fatigue and persistent carbohydrate cravings
• In women: irregular menstrual cycles, acne, and excess facial or body hair (reflecting insulin-driven androgen excess)

Diagnosis relies on laboratory testing, typically available through LifeLabs or Dynacare across Canadian provinces:

1. Fasting insulin — the most direct available clinical marker; elevated fasting insulin indicates compensatory hyperinsulinaemia
2. HOMA-IR (Homeostatic Model Assessment of Insulin Resistance) — calculated from fasting glucose and fasting insulin; a score above 2.5–3.0 is considered clinically significant
3. Fasting glucose and HbA1c — to determine whether insulin resistance has progressed to prediabetes or type 2 diabetes
4. Fasting lipid panel — the characteristic dyslipidaemia of insulin resistance (elevated triglycerides, low HDL) is a strong associated finding
5. Oral glucose tolerance test (OGTT) — provides a dynamic picture of glucose and insulin responses over two hours

Note that fasting insulin is not included in standard provincial lab panels in most Canadian provinces and may require a specific physician requisition.

Treatment options

Insulin resistance is highly responsive to intervention, particularly when addressed early.

Lifestyle — the most effective first-line approach:

• Weight loss of 5–10% of body weight produces significant improvements in insulin sensitivity
• Both aerobic exercise and resistance training improve muscle glucose uptake; the effect is rapid and does not require weight loss to occur
• Dietary patterns that reduce refined carbohydrates, added sugars, and ultra-processed foods — and increase fibre, protein, and unsaturated fats — consistently improve insulin signalling
• Achieving 7–9 hours of quality sleep per night restores insulin sensitivity impaired by sleep debt
• Stress reduction lowers chronic cortisol and directly improves insulin receptor function

Medications:

• Metformin — the most widely used insulin-sensitizing agent; reduces hepatic glucose output and is used in prediabetes, type 2 diabetes, and PCOS; covered under most provincial drug benefit formularies in Canada when criteria are met
• GLP-1 receptor agonists (semaglutide, liraglutide) — reduce appetite, promote weight loss, and substantially improve insulin sensitivity; coverage varies by province and indication
• SGLT2 inhibitors — promote renal glucose excretion and improve insulin sensitivity; also carry cardiovascular and renal protective benefits
• Thiazolidinediones (pioglitazone) — directly improve insulin sensitivity in fat, muscle, and liver; used less frequently today due to side-effect profile

When to see a clinician in Canada

Seek assessment from a family physician or nurse practitioner if any of the following apply:

• Waist circumference above 102 cm (men) or 88 cm (women)
• Dark, velvety skin patches in body folds
• Irregular periods combined with excess facial or body hair (possible PCOS)
• Family history of type 2 diabetes plus personal overweight or sedentary lifestyle
• Fasting glucose or lipids flagged as borderline on routine bloodwork
• Persistent difficulty losing weight despite sustained dietary and exercise effort

Canadian patients seeking virtual assessment can compare services including Felix, Maple, Cleo, Phoenix, and others — but a family physician or endocrinologist remains the appropriate entry point for formal diagnosis and medication decisions. Diabetes Canada's online risk assessment tool (available at diabetes.ca) is a validated starting point for self-screening.

Limitations and open questions

Research is still emerging on several aspects of insulin resistance. The optimal cut-off values for HOMA-IR vary across published studies and no single universally accepted threshold has been adopted in Canadian clinical guidelines. Fasting insulin assays also lack standardisation across laboratories, which limits direct comparison of results between testing sites.

The long-term cardiovascular benefit of treating insulin resistance in people who have not yet developed type 2 diabetes — particularly with pharmacotherapy — remains an active area of investigation. Health Canada has not yet issued specific guidance on routine insulin resistance screening in asymptomatic adults. The relative contributions of diet composition versus total caloric intake to insulin sensitivity improvement are also debated, and individual responses to dietary interventions vary considerably. Whether certain populations — including Indigenous Canadians, who face disproportionate rates of type 2 diabetes — require different screening thresholds is an important equity question that current guidelines do not fully address.