Begin Main Content Area


What is Obesity?

Obesity is defined as having extra body fat that can negatively affect health. In rare cases, obesity may have a single cause, but it usually results from the interaction of several biological, behavioral, environmental, and genetic factors. Once considered a problem of willpower, laziness, or gluttony, obesity is now understood by the medical and scientific community to be a serious and chronic metabolic disease.

Obesity is usually diagnosed by measuring height and weight to calculate the Body Mass Index (BMI). While BMI is not a perfect indicator of having excess body fat (for example, very muscular people will have a high BMI even if they have low body fat), it is easy to calculate and is a good starting place for healthcare providers to determine the health of one's body weight.

The following BMI-based categories are used for adults:

  • Underweight: BMI < 18.5 kg/m2
  • Normal weight: BMI 18.5 to 24.9 kg/m2
  • Overweight: BMI 25 to 29.9 kg/m2
  • Obesity: BMI > 30 kg/m2
    • Class I obesity: BMI 30 to 34.9 kg/m2
    • Class II obesity: BMI 35 to 39.9 kg/m2
    • Class III obesity: BMI 40 kg/m2

For children and teens, BMI percentile based on age and sex is used to define these categories:

  • Underweight: <5th percentile
  • Normal or Healthy Weight: 5th to <85th percentile
  • Overweight: 85th to <95th percentile
  • Obesity: > 95th percentile

In Pennsylvania, according to the 2019 Behavioral Risk Factor Surveillance Survey and 2018-2019 Pennsylvania Growth Screening Index, 33 percent of Pennsylvania adults and 18 percent of Pennsylvania children in grades K-12 are affected by obesity.  Nationally, according to the Centers for Disease Control and Prevention (2017-2018), the prevalence of obesity is approximately 42 percent in adults and 19 percent in children.   

Obesity, like many other serious and chronic diseases, disproportionately affects some demographic groups. In both adults and children, the prevalence of obesity is higher in Hispanic and non-Hispanic Black individuals than in non-Hispanic White and non-Hispanic Asian individuals.

Health Risks

Having obesity is a risk factor for several additional diseases or health conditions.  These include type 2 diabetes, cardiovascular disease, obstructive sleep apnea, non-alcoholic fatty liver disease, arthritis, infertility, and many types of cancer. 

The risk of developing many of these conditions – and the severity of many weight-related complications – can be reduced with weight loss, even if obesity remains.  Most medical organizations recognize a 5-10 percent weight loss as "clinically significant," meaning that a weight loss of this size may be sufficient to show a meaningful improvement in health.

The COVID-19 pandemic increased the focus on obesity as a risk factor for disease. Studies show that while obesity does not increase the risk of becoming infected with the coronavirus that causes COVID-19, obesity increases the risk of serious disease, hospitalization, and death from infection.

Prevention and Treatment of Obesity

Obesity is a complex chronic disease that results from a combination of causes and contributing factors. Effective strategies to address obesity include policy, systems, and environment changes to support healthy behaviors. These may include increasing access to healthy foods, reducing health disparities, and developing communities to support safe and accessible physical activity and active transportation.

Learn about strategies of the Pennsylvania Obesity Prevention and Wellness Section through the State Physical Activity and Nutrition grant.

For treating obesity, two prominent sets of guidelines (one published by the American Association of Clinical Endocrinologists and the American College of Endocrinology, the other by the American Heart Association, American College of Cardiology, and The Obesity Society) lay out three categories of evidence-based options. 

Lifestyle-based treatments.  Evidence-based lifestyle-based treatments include a reduced-calorie diet, increased physical activity, and a program of behavioral counseling to support diet changes and activity recommendations.  Many communities are home to a certified National Diabetes Prevention Program site, which offers free lifestyle-based intervention to qualified individuals overweight or with obesity.  Additionally, some commercial programs and doctor-supervised programs offer high-quality lifestyle-based treatments.

Medications.  Several medications have been shown to have a favorable risk-benefit profile and have been approved by the US Food and Drug Administration for chronic weight management.  The currently approved medications act in different ways to reduce appetite or impact the way calories are absorbed in the body.  Your physician and/or an obesity medicine specialist can help you select the most appropriate medication.  While many dietary supplements make claims related to weight loss, supplements are not evaluated by the FDA for efficacy or safety.

Surgery. Weight loss surgery (also called bariatric surgery) is an option for many people with severe obesity.  Most procedures limit the amount of food that can be eaten at once and have metabolic effects that can reduce appetite and directly improve some aspects of health.  People who undergo bariatric surgery require long-term follow-up with their surgeon and care team to ensure the best results. 

  • Visit the American College of Surgeons website to find Centers of Excellence by the Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) bariatric surgery programs.  

Regardless of which treatment or treatments are pursued, obesity requires chronic care.  Just as blood pressure would be expected to increase if a well-controlled patient with hypertension stopped receiving anti-hypertensive medication, weight regain is expected when obesity care is discontinued. 


For patients with obesity and caregivers of children with obesity:

For providers:

Contact Information:
Obesity Prevention and Wellness Program
PA Department of Health
Room 1000 H & W Building
625 Forster St.
Harrisburg, PA 17120-0701
Phone: 717-787-5876