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​Obesity

Introduction

Obesity is a chronic disease that affects millions of adults, adolescents, and children in the United States. Obesity results from a combination of genetic susceptibility, biological pathways related to metabolism and body weight regulation, and environmental factors.

Although obesity is often attributed to poor dietary habits and lack of physical activity, the truth is more complicated. The complex processes by which the body converts food into energy can be influenced by chemicals in the environment (over which we have limited control) and genetics (over which we have no control).

According to the World Health Organization, obesity has nearly tripled since 1975. In the U.S., 42% of adults were considered obsess (2017-2018). Among major ethnic groups, only non-Hispanic Asian men (17.4%) and women (17.2%) had rates significantly lower than the average. Some 18.5% of children and adolescents in the U.S. (2015-2016), about 13.7 million, were obese. Childhood obesity is more common among Hispanics (25.8%) and non-Hispanic blacks (22%) than other population groups. The Centers for Disease Control and Prevention (CDC) compiles state-level estimates of obesity prevalence among U.S. adults.

Health Effects From ObesityPeople affected by obesity have a higher chance of developing serious health problems, including asthma, type 2 diabetes, high blood pressure, cardiovascular disease, stroke, and many cancers, which together are among the leading causes of preventable or premature death. Children with obesity may be at a greater risk for allergies.

Obesity is one of the signs of metabolic syndrome, along with high blood pressure, blood sugar, and cholesterol levels.

According to the CDC, overweight and obesity are associated with at least 13 types of cancer.

How Much Is too Much?Weight that is higher than what is considered healthy for a given height is described as overweight or obese, according to the Centers for Disease Control and Prevention. Body Mass Index (BMI), a measure of weight for height is an indicator of body fatness.

A BMI score of 18.5 to 24.9 is considered normal. For adults, “overweight” is defined as a BMI of 25 to 29.9, and “obese” is a BMI range of 30 to 34.9. A score of 35 or above is “severely obese.” Note that BMI can be used as a screening tool but is not diagnostic of the health of an individual.

Measurements of body fat distribution—whether fat is carried around the hips or the abdomen—are increasingly being used along with BMI as indicators of obesity. These measurements include the waist-to-hip ratio.
For children and adolescents younger than 20, overweight and obese are based on BMI-for-age growth charts, available from the CDC.

How Is the Environment Linked to Obesity?Increasingly, researchers are questioning whether poor nutrition and lack of exercise are the only factors responsible for the obesity epidemic. Since most of the increase in obesity has occurred in the past 40 years, genetics alone are likely not to blame. Other factors in the environment or behavioral activities may be triggering the current obesity epidemic.

Endocrine disruptors. Many endocrine disruptors are synthetic chemicals. We are exposed to them daily through their use in plastics, pesticides, industrial and household products, flame retardants, and as ingredients in some cosmetics.

One major way chemicals can contribute to obesity is by interfering with our hormones. Hormones are the messengers in the body’s endocrine system, which plays a fundamental role in metabolism—the conversion of food to energy. Some endocrine disruptors have been linked to various diseases, including diabetes.

Obesogens. Obesogens are a broad class of chemicals that disrupt metabolism. Endocrine disruptors are a subset of obesogens. These chemicals do not directly cause obesity, but they may increase our susceptibility to weight gain, especially when the exposures occur during fetal development or early in life.

The most sensitive time for exposure to obesogens is during early development—as a fetus or during the first years of life—when the body’s weight control mechanisms are being developed.

An international group of researchers conducted a comprehensive analysis of many suspected environmental obesogens. Their study provides strong evidence for how smoking, air pollution, and characteristics of the built environment contribute to childhood obesity risk.

Examples of chemical compounds that may be obesogens are:

  • Bisphenol A (BPA), found in many plastic products including food storage containers, has been linked to childhood obesity.
  • Flame retardants are associated with adverse health effects in animals and humans.
  • Pesticides and insecticides, such as DDT, have been linked to obesity and associated disease.
  • Phthalates, chemicals used to make plastics more flexible, are also found in some food packaging, cosmetics, children’s toys, and medical devices.
  • Polychlorinated biphenyls (PCBs), industrial chemicals that were used widely in the past in products such as paints, cements, fluorescent light ballasts, sealants, and adhesives.
  • Tributyltin, widely used as a fungicide and heat stabilizer in polyvinyl chloride (PVC) piping, has been linked to transgenerational obesity.


Obesogens are believed to work in several ways, such as changing:

  • How a person’s fat cells develop, meaning they may increase fat storage capacity or the number of fat cells.
  • How the body regulates feelings of hunger and fullness, or magnify the effects of high-fat and high-sugar diets.


Air pollution. Many different chemicals are found in air pollution, which may be endocrine disruptors and obesogens.

Childhood obesity is associated with multiple environmental factors, including early life exposure to smoking and air pollution. NIEHS research has found links between traffic-related air pollution (TRAP) and negative effects on gut health, which has been linked to the development of type 2 diabetes in overweight and obese adolescents.

Air pollution exposure during childhood might contribute to poor diets. In one study, adolescents with higher exposures to TRAP as children were 34% more likely to eat foods high in unhealthy trans fats, regardless of household income, parent education level, or proximity to fast-food restaurants.

People living in poorer neighborhoods tend to be more exposed to air pollution. An NIEHS-funded study in New York City found that prenatal exposure to air pollution was linked to childhood obesity.

What Is NIEHS Doing?Grant recipients in the NIEHS Obesity and Diabetes program study related environmental topics and exposures during different life stages. A list and descriptions of NIEHS-funded research projects focused on obesity are found on our Who We Fund webpage. This research will help achieve a better
understanding of the role of environmental factors in obesity and diabetes, which is necessary for developing prevention strategies.

NIEHS is part of the NIH Obesity Research Task Force, a multi-institute response to the epidemic. In 2018-2019, the Task Force confirmed ongoing challenges in its Strategic Plan.

NIEHS is a partner in the NIH-wide Environmental Influences on Child Health Outcomes (ECHO) study. The seven-year program will investigate how environmental factors affect child health and development.

Preventing or Reducing ObesityAlthough there is no simple solution, a nutritious diet and regular physical activity can help prevent obesity. You can also try to minimize exposure to environmental chemicals:

  • Reduce use of plastics, and do not use them in the microwave
  • Purchase furniture that has not been treated with flame retardants
  • Choose fragrance-free products


Further Reading

Stories from the Environmental Factor (NIEHS newsletter)


Printable Fact Sheets


Podcasts

  • Obesity and the Environment - With obesity rates rising, some scientists wonder whether there’s more to the story than simply too many calories. In this podcast, Bruce Blumberg highlights research on how certain environmental chemicals, called “obesogens,” could increase the chance of developing obesity.


Additional Resources

  • Diet & Nutrition – From NIH and other federal agencies, find resources to help you improve your health and reduce disease risk.
  • National Library of Medicine Medline Plus: Obesity – Links and definitions about obesity.
  • NIH Nutrition for Precision Health, powered by the All of Us Research Program – This research will explore how different people respond to different diets. Its results will help individuals and their health care providers create healthy, precise, and effective diet plans.
  • NIH Obesity Research – As the nation’s biomedical research agency, the NIH seeks to gain insights into the factors contributing to obesity and to design and test strategies for prevention and treatment. This webpage includes information on the NIH Obesity Research Task Force.
  • NIH Strategic Plan for Nutrition Research – The first NIH-wide strategic plan to advance nutrition research across a wide range of areas.
  • Obesogens: An Environmental Link to Obesity – Read a summary of the science on chemicals linked to obesity in this 2012 Environmental Health Perspectives article.
  • Overweight and Obesity, Healthy People 2030 – Under a cross-agency federal framework, the Healthy People initiative provides science-based, 10-year national objectives for improving the health of all Americans.
  • Physical Wellness Toolkit – Watching what you put into your body, how much activity you get, and your weight are important for keeping your body working properly. Positive physical health habits can help decrease your stress, lower your risk of disease, and increase your energy.
  • The Interplay Between Environmental Chemical Exposures and Obesity: Proceedings of a Workshop (2016) – The National Academies of Sciences, Engineering, and Medicine held a workshop at NIEHS to explore the role that chemical exposures may play in the development of obesity. Participants considered new approaches that go beyond the standard focus on energy intake and expenditure to combat the multifactorial problem of obesity.


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Last Reviewed: March 14, 2022

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Adult Overweight & Obesity   

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COVID-19: Obesity and Excess Weight Increase Severe Illness Risk; Racial and Ethnic Disparities Persist

Obesity is a common, serious and costly chronic disease.
Adult Obesity Facts

What are the latest statistics on adult obesity in the United States?
Defining Adult Overweight & Obesity

How is adult obesity measured?
Causes and Consequences
What contributes to overweight and obesity? What are the health risks?

Adult BMI Calculator
Use the Adult BMI calculator for adults ages 20 years old and older.
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Page last reviewed: March 31, 2021

Content source: Division of Nutrition, Physical Activity, and Obesity, National Center for Chronic Disease Prevention and Health Promotion

Strategies to Prevent & Manage Obesity    
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There is no single or simple solution to the obesity epidemic. It’s a complex problem and there has to be a multifaceted approach. Policy makers, state and local organizations, business and community leaders, school, childcare and healthcare professionals, and individuals must work together to create an environment that supports a healthy lifestyle. There are several ways state and local organizations can create a supportive environment to promote healthy living behaviors that prevent obesity.

State and Local ProgramsResources are available to help disseminate consistent public health recommendations and evidence-based practices for state, local, territorial and tribal public health organizations, grantees, and practitioners.

Knowing your body mass index (BMI), achieving and maintaining a healthy weight, and getting regular physical activity are all actions you can take for yourself to combat obesity.

Community EffortsTo reverse the obesity epidemic, community efforts should focus on supporting healthy eating and active living in a variety of settings. Learn about different efforts that can be used in early childhood care, hospitals, schools, and food service venues.

Healthy LivingThe key to achieving and maintaining a healthy weight isn’t short-term dietary changes; it’s about a lifestyle that includes healthy eating and regular physical activity.

  • Assessing Your Weight
    BMI and waist circumference are two screening tools to estimate weight status and potential disease risk.
  • Healthy Weight
    A high BMI can be an indicator of high body fatness. Visit the Healthy Weight Website; learn about balancing calories, losing weight, and maintaining a healthy weight.
  • ChooseMyPlateexternal icon
    Healthy eating habits are a key factor for a healthy weight. Visit the ChooseMyPlate Website; look up nutritional information of foods, track your calorie intake, plan meals, and find healthy recipes.
  • Physical Activity Basics
    Physical activity is important for health and a healthy weight. Learn about different kinds of physical activity and the guidelines for the amount needed each day.
  • Tips for Parents
    Learn about the seriousness of childhood obesity and how to help your child establish healthy behaviors.


Related Information
​Nutrition, Physical Activity and Obesity Prevention Strategies and Guidelines provides guidance for program managers, policy makers, and others on how to select strategies.

Defining Adult Overweight & Obesity

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Weight that is higher than what is considered healthy for a given height is described as overweight or obesity. Body Mass Index (BMI) is a screening tool for overweight and obesity.
Adult Body Mass IndexBMI is a person’s weight in kilograms divided by the square of height in meters. A high BMI can indicate high body fatness.

To calculate BMI, see the Adult BMI Calculator or determine BMI by finding your height and weight in this BMI Index Chartexternal icon.

  • If your BMI is less than 18.5, it falls within the underweight range.
  • If your BMI is 18.5 to <25, it falls within the healthy weight range.
  • If your BMI is 25.0 to <30, it falls within the overweight range.
  • If your BMI is 30.0 or higher, it falls within the obesity range.


Obesity is frequently subdivided into categories:

  • Class 1: BMI of 30 to < 35
  • Class 2: BMI of 35 to < 40
  • Class 3: BMI of 40 or higher. Class 3 obesity is sometimes categorized as “severe” obesity.


Note: For individuals, BMI is screening tool, but it does not diagnose body fatness or health. A trained health care provider should perform appropriate assessments to evaluate an individual’s health status and risks. If you have questions about your BMI, talk with your health care provider.

See the following table for an example.
Visit the Adult BMI Calculator to calculate BMI (for adults 20 years and older)

Adult Body Mass Index (BMI)HeightWeight RangeBMIConsidered
5′ 9″124 lbs or lessBelow 18.5Underweight
125 lbs to 168 lbs18.5 to 24.9Healthy weight
169 lbs to 202 lbs25.0 to 29.9Overweight
203 lbs or more30 or higherObesity
271 lbs or more40 or higherClass 3 Obesity

BMI does not measure body fat directly, but BMI is moderately correlated with more direct measures of body fat obtained from skinfold thickness measurements, bioelectrical impedance, underwater weighing, dual energy x-ray absorptiometry (DXA) and other methods 1,2,3. Furthermore, BMI appears to be strongly correlated with various adverse health outcomes consistent with these more direct measures of body fatness 4,5,6,7,8,9.
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For More Information


References

​1Garrow, J.S. & Webster, J., 1985. Quetelet’s index (W/H2) as a measure of fatness. Int. J. Obes., 9(2), pp.147–153.
2Freedman, D.S., Horlick, M. & Berenson, G.S., 2013. A comparison of the Slaughter skinfold-thickness equations and BMI in predicting body fatness and cardiovascular disease risk factor levels in children. Am. J. Clin. Nutr., 98(6), pp.1417–24.
3Wohlfahrt-Veje, C. et al., 2014. Body fat throughout childhood in 2647 healthy Danish children: agreement of BMI, waist circumference, skinfolds with dual X-ray absorptiometry. Eur. J. Clin. Nutr., 68(6), pp.664–70.
4Steinberger, J. et al., 2005. Comparison of body fatness measurements by BMI and skinfolds vs dual energy X-ray absorptiometry and their relation to cardiovascular risk factors in adolescents. Int. J. Obes., 29(11), pp.1346–1352.
5Sun, Q. et al., 2010. Comparison of dual-energy x-ray absorptiometric and anthropometric measures of adiposity in relation to adiposity-related biologic factors. Am. J. Epidemiol., 172(12), pp.1442–1454.
6Lawlor, D.A. et al., 2010. Association between general and central adiposity in childhood, and change in these, with cardiovascular risk factors in adolescence: prospective cohort study. BMJ, 341, p.c6224.
7Flegal, K.M. & Graubard, B.I., 2009. Estimates of excess deaths associated with body mass index and other anthropometric variables. Am. J. Clin. Nutr., 89(4), pp.1213–1219.
8Freedman, D.S. et al., 2009. Relation of body mass index and skinfold thicknesses to cardiovascular disease risk factors in children: the Bogalusa Heart Study. Am. J. Clin. Nutr., 90(1), pp.210–216.
9Willett, K. et al., 2006. Comparison of bioelectrical impedance and BMI in predicting obesity-related medical conditions. Obes. (Silver Spring), 14(3), pp.480–490.
Page last reviewed: June 7, 2021

Content source: Division of Nutrition, Physical Activity, and Obesity, National Center for Chronic Disease Prevention and Health Promotion

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Overweight & Obesity
alert icon
COVID-19: Obesity and Excess Weight Increase Severe Illness Risk; Racial and Ethnic Disparities Persist

High BMI can Increase Risk for Flu Complications

Adults with severe obesity are more likely to develop complications from the flu.
Preventing Childhood ObesityFive things you can do at home.
2020 Adult Obesity Prevalence MapsSelf-reported adult obesity prevalence by race, ethnicity, and location
Addressing Childhood Obesity: CORD 3.0.Building on previous Childhood Obesity Research Demonstration projects
Early Care and Education (ECE)ECE settings can support healthy eating and physical activity among young children.
High BMI can Increase Risk for Flu ComplicationsAdults with severe obesity are more likely to develop complications from the flu.
Preventing Childhood ObesityFive things you can do at home.
2020 Adult Obesity Prevalence MapsSelf-reported adult obesity prevalence by race, ethnicity, and location
Addressing Childhood Obesity: CORD 3.0.Building on previous Childhood Obesity Research Demonstration projects
Early Care and Education (ECE)ECE settings can support healthy eating and physical activity among young children.
High BMI can Increase Risk for Flu ComplicationsAdults with severe obesity are more likely to develop complications from the flu.
DC’s Obesity efforts focus on policy and environmental strategies to make healthy eating and active living accessible and affordable for everyone.

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Childhood Overweight & ObesityDefining childhood overweight and obesity, facts, causes and health consequences
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Adult Overweight & ObesityDefining adult overweight and obesity, facts, causes and health consequences
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Strategies to Prevent ObesityObesity prevention strategies to create an environment that supports healthy lifestyles
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CDC InitiativesChildhood Obesity Research Demonstration Projects (CORD), Clinical and Community Data Initiative (CODI), COMMIT!

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Data & StatisticsLatest statistics on U.S. obesity, maps , interactive databases and data systems
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Resources & PublicationsReports, prevention strategies and guidelines, fact sheets, social media tools

Healthy WeightMaintaining a healthy weight contributes to good health now and as you age.
State and Local ProgramsCheck out the latest state initiatives related to nutrition, physical activity, and healthy weight.
Recursos en EspañolSpanish language resources for healthy weight, nutrition, and physical activity.
In the Spotlight


Notes on Language and Images:
We encourage the use of person-first language and respectful images when discussing obesity and other chronic diseases. For example, say “adults with obesity” or “20% of children ages 12-19 have obesity” rather than “obese adults” or “20% of children are obese”.

The Obesity Action Coalition has more information – please see the Guidelines for Media Portrayals of Individuals Affected by Obesitypdf iconexternal icon. [PDF-1.72MB]

Page last reviewed: February 17, 2022

Content source: Division of Nutrition, Physical Activity, and Obesity, National Center for Chronic Disease Prevention and Health Promotion
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