Obesity
Obesity is a chronic disease of excess adiposity, defined by a body mass index of 30 or greater, that raises risk for type 2 diabetes, cardiovascular disease, sleep apnea, liver disease, and several cancers. Management is staged: lifestyle intervention for all patients, pharmacotherapy after 3 to 6 months of unmet lifestyle goals, and bariatric surgery for a body mass index of 40 or greater or 35 or greater with a comorbidity.
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What this article covers
- Overview
Obesity is chronic excess adiposity defined by a body mass index (BMI) of 30 kg/m² or greater, a threshold used because it correlates with disease risk across large populations, not because it directly measures body fat.
- Epidemiology
The United States has the highest obesity rate among developed countries, with obesity prevalence of 39.8% and combined overweight-or-obesity prevalence (BMI 25.0 or greater) of 71.8%.
- Risk factors
A calorie intake that chronically exceeds energy expenditure is the proximate driver.
- Pathophysiology
Obesity results from a sustained imbalance between energy intake and expenditure, with excess energy stored as triglyceride in expanded adipocytes, predominantly in visceral and subcutaneous depots.
- Clinical features
The disease is defined and staged by BMI, not by a symptom complex, so assessment centers on quantifying adiposity and identifying weight-related comorbidity rather than eliciting a classic syndrome.
- Differential diagnosis
Hypothyroidism: causes modest weight gain with fatigue and cold intolerance, unlike primary obesity, distinguished by an elevated thyroid-stimulating hormone level.
- Diagnosis
The diagnosis is established by calculating BMI from measured height and weight; a BMI of 30 kg/m² or greater defines obesity, with overweight at 25.0-29.9.
- Management
First, engage every patient using nonjudgmental language and assess readiness to change, since engagement affects adherence to any subsequent intervention.
- Complications
Type 2 diabetes mellitus, driven by adipose-tissue-mediated insulin resistance.
- Prognosis
Midlife obesity is associated with increased dementia risk later in life, beyond its cardiometabolic consequences.
- Prevention
The U.S. Preventive Services Task Force recommends screening all adults for obesity by calculating BMI, with referral to intensive behavioral intervention for a BMI of 30 or greater.
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Type 2 diabetes is hyperglycemia from insulin resistance with progressive relative insulin deficiency, diagnosed by a hemoglobin A1c of 6.5% or higher, a fasting glucose of 126 mg/dL or higher, or a 2-hour oral glucose tolerance test value of 200 mg/dL or higher. First-line treatment is lifestyle modification plus metformin, with an SGLT2 inhibitor or GLP-1 receptor agonist added early for patients with atherosclerotic disease, kidney disease, or heart failure.
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- Sleep apnea
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- Asthma
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