Obesity

The rates of obesity in the United States reflect the global trend, with adult rates tripling since 1960. Currently over 40% of adults in the US have obesity.² Obesity is indicated by a Body Mass Index (BMI) over 30. This measure is not always accurate in diagnosing obesity, but it is useful for public health screening.

Race and Ethnicity. Race and ethnicity influence the risk of obesity in the United States, with non-Hispanic Black adults and Hispanic adults experiencing the highest rates.⁶

Socioeconomic Status. Higher educational attainment has consistently been associated with a lower risk of obesity in white women. The association is less clear or consistent in men and non-white women.⁷ A similar pattern was found in an earlier report that included income: the prevalence of obesity in white, non-Hispanic females of all ages falls as family income rises. A similar association was found in white, non-Hispanic males aged 2-19, but the association is weak or even reversed in other groups.⁸ Thus there is some connection between income, educational attainment and risk of obesity, but it is not always consistent or conclusive. See CHE's Socioeconomic Environment webpage.

Research has found that low-income communities and communities of color have more limited access to healthful foods than other communities.⁹ The availability of healthy food options in a community often goes unnoticed in the background, but it can play a major role in people’s ability to eat healthy.¹⁰

Related Health Problems

People with obesity are at increased risk for a variety of health problems including: ¹¹

• Type 2 diabetes
• Cardiovascular disease (CVD), including stroke
• High blood pressure (hypertension)
• Arthritis
• Breathing problems
• Some cancers, especially of the esophagus, pancreas, colon and rectum, breast (after menopause), endometrium (lining of the uterus), kidney, thyroid, and gallbladder¹²
• Early puberty¹³
• Metabolic syndrome¹⁴

Many factors are known to contribute to obesity, including chemical exposures, genetics, and other lifestyle factors, which we discuss here in turn. Increasing evidence shows that environmental exposures are a key driver of the increasing obesity trends.¹⁵

Obesogens and Endocrine Disrupting Chemicals

Chemicals that promote fat development are referred to as obesogens. According to the National Institute of Environmental Health Sciences (NIEHS), these exposures may not cause obesity directly, but are thought to increase an individual’s susceptibility for gaining weight, especially when exposure occurs during development, in infancy, and childhood.¹⁶

Many of the chemicals linked to obesity are part of a group called endocrine disrupting chemicals (EDCs). EDCs are found in many everyday products, including plastics, detergents, flame retardants, food, toys, cosmetics, and pesticides. EDCs can alter the hormonal signals that control and guide much of our growth and development, the way our organs function, and our ability to fight disease. 

Obesogenic EDCs are thought to stimulate adipogenesis (the process by which fat-storing cells develop and accumulate lipids). Adipogenesis is the key cellular process that leads to obesity.¹⁸ See our EDCs webpage for more details. See Diabetes and the Environment: Obesogens for more on the latest science around obesogens.

Here we highlight some chemicals to which large numbers of people are regularly exposed and which show strong evidence of acting as obesogens.¹⁹

Genetics and Epigenetic Programming

Genes play a role in obesity, causing some obesity disorders. However, having a specific gene variant, or set of variants, does not always mean that an individual will have obesity. Often with genetic components of diseases and disorders, an individual's environment—nutrition, activity, chemical exposures, sleep quality and so on—can either promote or inhibit the physical expression of genes.

The term "epigenetic programming" refers to mechanisms that can turn on or off genes or sections of chromosomes, changing their functioning. These changes are maintained as the cell replicates, and some research has shown that these changes can pass down to offspring. Changes in a fetus's genes by the mother's nutritional status during pregnancy are an example of epigenetic programming.²² Studies have identified multiple potential epigenetic mechanisms through which obesogenic chemicals could be contributing to obesity rates.²³

For more information on genes and the environment, see our Gene-Environment Interactions webpage.

Other Factors

Diet and Exercise. An energy-dense diet, and especially foods high in fat and/or sugar,²⁴ and lack of exercise and physical activity are strongly associated with obesity.²⁵

Mother's Nutrition. Severe undernourishment (famine) by a pregnant woman has been associated with an increased risk of obesity in her child. When the mother is malnourished, the baby's genes involved with appetite regulators, pancreatic development, and obesity-associated genes can be affected, and these changes can last throughout the child's life.²⁶

Maternal obesity also increases the risk of developing insulin resistance and has been associated with an increased risk of large gestational weight, fat accumulation, and type 2 diabetes in youth.²⁷

Sleep and Stress. Evidence also links both sleep and stress to obesity.²⁸ Research has found a strong association between individuals' working night shifts and increased body weight,²⁹ with some evidence that poor sleep quality causes negative changes in metabolic, inflammatory, neuroendocrine, and antioxidant biomarkers.³⁰ See our Psychosocial Environment page for more information on the effects of stress on health.

Obesity is a complex issue that involves many aspects of society. To best prevent the development of obesity and to support those who have obesity, community responsibility must be addressed along with individual choices. 

Community, governmental, and societal actions are needed to provide health-promoting food options, encourage physical activity, educate the public, and regulate the foods and chemicals that are associated with obesity.

Healthy Eating and Physical Activity

Modern society has reworked our systems of food and agriculture to make unhealthy food choices both more available and less expensive than healthier foods (see our Food and Agriculture Environment webpage). In addition, many neighborhoods, transportation systems, work and school environments, and recreational activities have likewise been altered or engineered to promote less physical activity as the norm in our lives³¹ (see our Built Environment webpage).

Governmental interest in addressing obesity is increasing, in part because of the huge economic and societal costs. Government actions include these:

• The World Health Organization's (WHO) lowering of sugar intake recommendations in 2015³²
• 2021 Healthy Food Service Guidelines from the CDC³³
• The US Food and Drug Administration's 2016 changes to food labeling rules³⁴
• New York City's efforts to curtail soda consumption³⁵
• CDC's Physical Activity Guidelines, updated in 2018³⁶
• WHO's 2020 Guidelines on Physical Activity and Sedentary Behaviour³⁷

Harvard’s School of Public Health outlines some policy suggestions that could help improve access to healthy food choices:

“Agriculture policy can focus on increased planting and buying of fresh fruits and vegetables. Revenue policy can focus on increasing taxes on unhealthy foods and subsidizing the cost of healthy choices. Zoning regulations can help bring supermarkets to low-income neighborhoods and limit fast-food restaurants in areas where there are already too many. And communication policy can restrict advertising to youth about unhealthy foods, or curb stealth marketing to youth through junk food product placements on prime-time television.”³⁸

Reducing Obesogen Exposures

Policies that encourage healthy eating and physical activity seek to address energy intake and expenditure. However, this is not the whole picture. Obesogens change our metabolic processes, altering the balance between energy intake and energy expenditure, and increasing the overall prevalence of obesity. These hormone disrupting chemicals are found in consumer and industrial products like makeup, shampoos, soaps, plastics, cleaners, pesticides, and food packaging. 

Reducing exposures can play a critical role in preventing obesity. Exposure occurs throughout the life course, starting even before conception. Research shows that the most sensitive time for obesogen action is in utero and early childhood.³⁹ Therefore, we need government leadership to more thoroughly test and regulate potentially obesogenic chemicals.

Medical and social costs

Studies estimating costs of obesity-related illness in the United States show total costs in the billions. Studies in 2011 and 2021 estimate medical costs to be between $190 billion and $260 billion per year.⁴⁰

These estimates do not include many indirect costs of obesity, such as work absences, decreased productivity while at work, and premature mortality and disability.⁴¹ An economic review of obesity discovered that obesity is among the most costly preventable diseases.⁴²

Impacts of Weight Stigma

A recent BioMed Central article defined weight stigma as the "social rejection and devaluation that accrues to those who do not comply with prevailing social norms of adequate body weight and shape." Weight stigma is a form of discrimination based on a person's body weight.⁴³

Individual behavior is often called into question regarding why an individual may have obesity or be overweight. These attitudes fail to take into account other contributing factors, such as environmental exposures outside of a person’s control, genetics, and social determinants of health.⁴⁴  

Studies have shown that even physicians show strong weight stigma in healthcare situations.⁴⁵ This stigma impacts many aspects of psychological well-being and may also result in sub-optimal clinical outcomes for patients.⁴⁶ This can have real impacts on both psychological and physical health.