This article was created with Dr. Timothy Garvey, Professor of Medicine in the Department of Nutrition Sciences at the University of Alabama at Birmingham. This article was edited by Elizabeth Hyska.
More than 42% of U.S. adults now live with obesity, according to the latest data from the Centers for Disease Control and Prevention. Among children and adolescents, the number has quadrupled since the 1970s, with nearly one in five affected.
Doctors say the trend has reached a tipping point — and the conversation is shifting from how much someone weighs to how that weight affects the body.
“Obesity isn’t diagnosed by size alone; it’s diagnosed when excess body fat impairs organ or tissue function.” – Paraphrased from the Lancet Commission on Obesity, 2024
Beyond the BMI
For decades, body mass index — a person’s weight in kilograms divided by their height in meters squared — has been the standard measure of obesity. But BMI alone is a blunt tool.
Physicians increasingly rely on additional measures:
- Waist circumference, where more than 40 inches in men or 35 inches in women, signals a higher risk.
- Waist-to-hip ratio, which reflects fat distribution. Usually, 0.85 or less for women and 0.9 or less for men is considered healthy.
- DEXA scans, which precisely measure fat and lean tissue.
Where the fat sits matters, android, or visceral obesity — fat stored in the abdomen — carries a higher risk for metabolic disease than gynoid obesity, which is stored in the hips and thighs.
A Complex Condition
Obesity has many causes. Some cases are genetic, such as Prader–Willi syndrome or leptin deficiency. Others are secondary to medical conditions like hypothyroidism or Cushing’s syndrome, or triggered by medications including corticosteroids and some antidepressants.
The majority of cases are primary obesity, driven by a mix of lifestyle, environment, and genetic susceptibility.
When Fat Becomes a Threat
Far from being inert storage, fat tissue is metabolically active. In excess, it releases inflammatory chemicals, causes scarring in tissues, and deposits in organs where it doesn’t belong — a process called ectopic fat deposition.
When these changes start to disrupt organ function, obesity becomes clinical obesity. The effects can be far-reaching:
- Brain: headaches, vision loss from increased intracranial pressure.
- Airway: sleep apnea.
- Lungs: shortness of breath, wheezing.
- Heart and blood vessels: heart failure, atrial fibrillation, pulmonary hypertension, high blood pressure, and blood clots.
- Metabolism: high triglycerides, low HDL cholesterol, elevated blood sugar.
- Liver: fatty liver disease, NASH.
- Kidneys: chronic kidney disease, protein leakage in urine.
- Reproductive system: polycystic ovary syndrome, infertility, low testosterone.
- Joints and mobility: osteoarthritis, swelling, reduced range of motion, impaired daily activity.
- Depression
- Cancer: to date, obesity has been related to 13 different types of cancer.
The Obesity Spectrum: Pre-Clinical to Severe
At one end is pre-clinical obesity — excess fat without organ damage yet, offering a critical window for intervention. At the other end is severe obesity, defined as a BMI over 40, where organ complications are almost always present.
Why Language Around Obesity Matters
In 2013, the American Medical Association classified obesity as a disease. Advocates say that the label helps focus public health policy, improve insurance coverage for treatment, and reduce the stigma that obesity is purely a matter of willpower.
By calling it a disease, we can direct resources toward both prevention and treatment. It also shifts the conversation from blame to solutions.
The Bottom Line
The shift from seeing obesity as “extra weight” to recognizing it as a medical condition could reshape how America responds to one of its most urgent health crises. For millions, the question isn’t simply “Am I heavier than last year?” It’s “Is my weight now harming my health?”
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