Obesity

What it is

Obesity is a chronic, multifactorial disease defined by excess body fat sufficient to impair health, affecting approximately 27% of Canadian adults — with a further 36% classified as overweight — according to Obesity Canada's 2020 Clinical Practice Guidelines. Also called adiposity-based chronic disease (ABCD) in some clinical frameworks, obesity is diagnosed primarily by body mass index (BMI), where a BMI of 30 or above meets the threshold, though waist circumference and metabolic markers are increasingly recognized as essential supplements to BMI alone.

Major medical organizations — including Obesity Canada, the Endocrine Society, and the Canadian Medical Association — now classify obesity as a chronic disease driven by biology, not a failure of willpower. It substantially raises the risk of type 2 diabetes, cardiovascular disease, obstructive sleep apnea, certain cancers (endometrial, breast, colon, kidney), osteoarthritis, polycystic ovary syndrome (PCOS), and depression. Understanding obesity as a disease with identifiable biological drivers changes how it is evaluated and treated.

Causes and mechanism

Obesity results from a sustained imbalance between energy intake and expenditure, but the mechanisms behind that imbalance are numerous and interacting.

Hormonal and metabolic drivers

Several hormonal systems regulate hunger, satiety, fat storage, and energy use. When these systems are disrupted, weight gain becomes biologically entrenched:

• Leptin resistance: Leptin is the satiety hormone produced by fat cells. In obesity, the brain becomes resistant to leptin's signals and fails to register fullness, perpetuating overeating.
• Ghrelin dysregulation: Ghrelin is the hunger hormone; its levels rise disproportionately after weight loss, driving appetite and making long-term maintenance genuinely difficult.
• Insulin resistance: Promotes fat storage and impairs the body's ability to mobilize stored fat for energy.
• Cortisol excess: Chronic stress elevates cortisol, favouring visceral (abdominal) fat accumulation — an effect particularly pronounced in women with obesity, according to recent research.
• Thyroid dysfunction: Hypothyroidism reduces basal metabolic rate and contributes to weight gain.
• Low testosterone in men: Associated with central fat accumulation and reduced lean muscle mass.
• Gut microbiome alterations: An imbalanced gut microbiome influences caloric extraction from food and metabolic hormone signalling, including GLP-1 and peptide YY.

Genetic factors

Heredity accounts for 40–70% of BMI variation. Rare single-gene mutations (e.g., MC4R variants) cause severe early-onset obesity in a subset of individuals.

Environmental and behavioural factors

Factor	Mechanism
Ultra-processed food environments	High caloric density, low satiety signalling
Sedentary lifestyle	Reduced energy expenditure
Sleep deprivation	Impairs leptin/ghrelin balance
Weight-promoting medications	Antipsychotics, corticosteroids, insulin, some antidepressants
Socioeconomic barriers	Food insecurity, limited access to safe physical activity

Symptoms and diagnosis

Obesity itself produces few direct symptoms, but its downstream effects touch virtually every organ system.

Physical signs

• BMI at or above 30
• Waist circumference above 88 cm in women or 102 cm in men (reflecting visceral fat burden)
• Reduced exercise tolerance and exertional breathlessness
• Joint pain, particularly knees and hips
• Obstructive sleep apnea: loud snoring and non-restorative sleep
• Skin changes: acanthosis nigricans, intertrigo, stretch marks

Associated conditions: type 2 diabetes, hypertension, dyslipidaemia (elevated triglycerides, low HDL), non-alcoholic fatty liver disease, PCOS, infertility, depression, and anxiety.

Diagnostic workup

1. BMI calculation: weight (kg) ÷ height (m²)
2. Waist circumference measurement
3. Metabolic panel: fasting glucose, HbA1c, lipid panel, liver enzymes, blood pressure
4. Hormonal evaluation: TSH, fasting insulin, testosterone in men; cortisol if Cushing's syndrome is suspected
5. Sleep study if obstructive sleep apnea is suspected

In Canada, initial bloodwork is typically ordered through a family physician and processed at provincial labs such as LifeLabs or Dynacare.

Treatment options

Effective obesity management is multidisciplinary, addressing behaviour, biology, and — where indicated — pharmacology or surgery.

Lifestyle interventions

• Dietary modification: a sustainable caloric deficit through a whole-foods-based diet; Mediterranean, low-glycaemic, and low-carbohydrate approaches all have supporting evidence.
• Physical activity: 150–300 minutes per week of moderate-intensity aerobic activity, combined with resistance training to preserve lean mass.
• Behavioural therapy: cognitive behavioural therapy (CBT) and motivational interviewing address emotional eating and long-term adherence.

Pharmacological treatment

• GLP-1 receptor agonists (semaglutide as Wegovy/Ozempic; liraglutide as Saxenda): currently the most effective medications for obesity. Clinical trials show average weight loss of 12–15% of body weight with high-dose semaglutide over 68 weeks, alongside improvements in blood pressure, blood sugar, and triglycerides.
• Naltrexone-bupropion (Contrave): reduces appetite and food cravings through central mechanisms.
• Orlistat: reduces dietary fat absorption in the gut.

Coverage for these medications varies by province; some provincial drug benefit plans cover Saxenda or Contrave under specific criteria. Canadians can also access obesity pharmacotherapy through virtual care platforms — options include Felix, Maple, Cleo, Phoenix, and others — though coverage and prescribing criteria differ.

Bariatric surgery Indicated for BMI above 40, or above 35 with significant obesity-related comorbidities. Sleeve gastrectomy and Roux-en-Y gastric bypass produce 20–30% body weight loss and frequently lead to remission of type 2 diabetes. Wait times through the public system vary considerably by province.

Treating underlying hormonal causes Where identified: levothyroxine for hypothyroidism, testosterone replacement for hypogonadal men, and targeted treatment of Cushing's syndrome or PCOS.

When to see a clinician in Canada

Seek assessment from a family physician or endocrinologist if:

• Your BMI is 30 or above, or waist circumference exceeds 88 cm (women) or 102 cm (men)
• You have not been able to sustain weight loss despite consistent lifestyle efforts
• You have obesity-related conditions such as type 2 diabetes, hypertension, or sleep apnea
• You want to explore pharmacological or surgical options
• You would like a hormonal workup to rule out thyroid dysfunction, insulin resistance, Cushing's syndrome, or hypogonadism as contributing factors

Obesity Canada's 2020 guidelines explicitly call for weight-neutral, compassionate care that treats obesity as a chronic disease — patients have the right to expect the same evidence-based approach applied to any other long-term condition.

Limitations and open questions

Research is still emerging on several fronts. The long-term safety and efficacy of GLP-1 receptor agonists beyond five years remain under study, and it is not yet clear which patients will maintain weight loss after stopping these medications. The clinical utility of body fat percentage and visceral fat imaging over BMI has not been standardized in Canadian clinical guidelines. Health Canada has not yet issued formal guidance on the sequencing of pharmacological agents for obesity management. The role of the gut microbiome in obesity causation — versus correlation — remains an active area of investigation, and microbiome-targeted therapies are not yet validated for clinical use. Additionally, the interaction between socioeconomic determinants of health and biological obesity risk is incompletely understood, and current treatment models do not fully account for structural barriers many Canadians face in accessing care.