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Causes of Overweight and Obesity: A Multifactorial Framework

Overweight and obesity result from sustained positive energy balance modulated by genetic, environmental, behavioral, and physiological factors. No single cause explains all cases; understanding the interplay enables effective intervention.

Major Contributing Factors

1. Dietary Patterns

Caloric density: Ultra-processed foods (UPFs) deliver more calories/gram with lower satiety
Added sugars: Sugar-sweetened beverages (SSBs) — liquid calories don't trigger fullness
Refined carbohydrates: Rapid glucose/insulin spikes → hunger rebound
Portion distortion: Larger servings, "supersizing," package size effects
Food environment: Ubiquitous, inexpensive, heavily marketed UPFs

2. Physical Inactivity

Sedentary occupations, screen time, motorized transport
NEAT (non-exercise activity thermogenesis) decline — major contributor
Exercise alone rarely offsets caloric excess without dietary change

3. Genetic and Epigenetic Factors

Heritability of BMI: 40–70% (twin/adoption studies)
Polygenic: >1,000 loci identified (FTO, MC4R, etc.); each small effect
Monogenic obesity rare (leptin, MC4R, POMC mutations)
Epigenetics: In utero exposures (maternal obesity, diabetes, famine) program metabolic set points

4. Hormonal and Metabolic Dysregulation

Insulin resistance: Promotes fat storage, inhibits lipolysis
Leptin resistance: Impaired satiety signaling despite high leptin
Thyroid dysfunction: Hypothyroidism → modest weight gain
PCOS: Hyperinsulinemia + hyperandrogenism → central adiposity
Cushing's syndrome: Cortisol excess → visceral fat
Growth hormone deficiency

5. Medications (Iatrogenic Weight Gain)

6. Sleep and Circadian Disruption

Short sleep (<7 hrs): ↑ ghrelin, ↓ leptin, ↑ cortisol, ↑ hunger for calorie-dense foods
Shift work: Circadian misalignment → metabolic dysregulation
Sleep apnea: Bidirectional with obesity

7. Psychosocial Factors

Emotional eating, stress-induced cortisol, food insecurity
Adverse childhood experiences (ACEs) → long-term metabolic risk
Weight stigma → avoidance of care, disordered eating

8. Environmental and Societal Determinants

Food deserts/swamps (access to healthy vs. unhealthy food)
Built environment (walkability, parks, safety)
Socioeconomic status (inverse gradient in high-income countries)
Marketing to children, agricultural subsidies (corn, soy → cheap calories)

Integrated Management Approach

Effective treatment addresses multiple levels simultaneously:

Individual: Nutrition therapy, physical activity, behavioral counseling, pharmacotherapy (GLP-1 agonists, etc.), bariatric surgery
Clinical: Bias-free care, comorbidity management, medication review
Community: Food policy, urban design, school/workplace wellness
Societal: Regulation, taxation (SSBs), subsidy reform, stigma reduction

Obesity is a complex chronic disease—not a personal failing. Comprehensive, compassionate, evidence-based care across all levels is required.

Obesity - Related Articles

Class	Examples	Mechanism
Antipsychotics	Olanzapine, clozapine, quetiapine	H1 blockade, metabolic
Antidepressants	Mirtazapine, paroxetine, TCAs	Appetite ↑, metabolic
Corticosteroids	Prednisone >7.5 mg/day chronic	Insulin resistance, fat redistribution
Antidiabetics	Insulin, sulfonylureas, TZDs	Anabolic, hypoglycemia-driven eating
Antiepileptics	Valproate, gabapentin, pregabalin	Appetite ↑
Beta-blockers	Older non-selective (propranolol)	Thermogenesis ↓, fatigue