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Obesity is a common, complex, and treatable chronic disease in which excess body fat accumulates to a degree that harms health. It is not simply a matter of willpower or appearance. Major medical organizations recognize obesity as a disease influenced by genetics, biology, behavior, and environment.
The most widely used screening measure is body mass index (BMI), calculated from height and weight. In adults, BMI categories are commonly defined as:
According to the CDC, about 40% of US adults had obesity during August 2021-August 2023 (40.3%), including roughly 9% with severe obesity (9.4%). Recent CDC data also estimate that about 21% of US children and adolescents ages 2-19 had obesity.
BMI is a useful population screening tool but an imperfect individual measure because it does not directly measure body fat or where fat is stored. A 2025 Lancet Commission proposed distinguishing *clinical obesity* (excess fat that is actively causing organ or tissue dysfunction) from *preclinical obesity* (excess fat with increased future risk but no current organ damage), using additional measures such as waist circumference.
Obesity develops when, over time, the body stores more energy (calories) than it uses, but the reasons behind that imbalance are rarely simple. Contributing causes and risk factors include:
Obesity itself may not cause obvious day-to-day symptoms, but it significantly raises the risk of many serious conditions. According to the NIH and the National Cancer Institute, obesity is linked to:
Clinicians typically begin with BMI and a physical exam. Because BMI alone is limited, evaluation increasingly includes:
This broader assessment helps determine whether excess weight is already affecting health and guides individualized care.
Obesity is treatable, and research suggests even 5-10% weight loss can meaningfully improve blood sugar, blood pressure, cholesterol, and joint pain. Treatment is usually layered and long-term:
Lifestyle foundation
FDA-approved medications (with lifestyle changes) The FDA has approved six drugs for long-term weight management: orlistat, phentermine-topiramate, naltrexone-bupropion, liraglutide, semaglutide (Wegovy), and tirzepatide (Zepbound). The newer GLP-1-based medicines are the most effective, with average weight loss of roughly 13-22% in trials depending on the drug and dose. These require a prescription and clinical monitoring, and they carry potential side effects.
Bariatric (metabolic) surgery For people with severe obesity (generally BMI 40 or higher, or 35 or higher with serious complications), procedures such as sleeve gastrectomy and Roux-en-Y gastric bypass are the most effective long-term treatment and can improve or resolve conditions like type 2 diabetes.
Talk with a healthcare provider if you have a BMI of 30 or higher, a BMI of 25-29.9 with weight-related health problems, a rising waistline, or conditions such as diabetes, high blood pressure, or sleep apnea. Seek care sooner if you experience chest pain, severe shortness of breath, or signs of depression. A clinician can confirm a diagnosis, screen for complications, and build a safe, personalized plan.
*This article is for general information only and is not medical advice. Always consult a qualified healthcare professional about your individual health and before starting any treatment.*
The US Food and Drug Administration (FDA) has approved six medications for long-term ("chronic") weight management in adults: orlistat (Xenical, Alli), phentermine-topiramate ER (Qsymia), naltrexone-bupropion (Contrave), liraglutide (Saxenda), semaglutide (Wegovy), and tirzepatide (Zepbound). The newer GLP-1 and GIP/GLP-1 receptor agonists are the most effective: in clinical trials, semaglutide produced roughly 13-15% average body-weight loss and tirzepatide about 20% (up to roughly 21-22% at the highest dose) over about 68-72 weeks, alongside diet and exercise. Wegovy is also FDA-approved to reduce the risk of cardiovascular death, heart attack, and stroke in adults with established cardiovascular disease plus obesity or overweight, and (August 2025) for adults with noncirrhotic metabolic dysfunction-associated steatohepatitis (MASH) with moderate-to-advanced liver fibrosis. An oral tablet form of semaglutide (oral Wegovy) was FDA-approved in December 2025. Older agents (orlistat, phentermine-topiramate, naltrexone-bupropion, liraglutide) typically produce about 3-11% weight loss. For severe obesity, bariatric (metabolic) surgery such as sleeve gastrectomy and Roux-en-Y gastric bypass is the most effective long-term treatment for eligible patients. All of these treatments carry risks and benefits and require evaluation, prescription, and monitoring by a qualified clinician. This is general information, not medical advice or a product endorsement.
This page is for general information and is not medical advice. Always consult a qualified clinician about diagnosis and treatment. Individual results vary.