By Angela Ryan Lee, MD 

 Medically reviewed by Jamie Johnson, RDN

Obesity is defined by a body mass index greater than 30 kilograms per square meter.¹ According to the Centers for Disease Control and Prevention (CDC), 4 in 10 American adults have obesity, and rates of obesity have risen substantially over the last few decades.² Obesity is associated with many serious health conditions, including heart disease, which is the leading cause of death. It is also associated with type 2 diabetes, cancer, arthritis, obstructive sleep apnea, and other conditions.³

This article will highlight important facts about obesity, including rates of obesity in different groups, complications associated with obesity, and prevention.

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Split Opinions on Obesity as a Disease

Screening for Obesity

Healthcare providers screen for obesity using the body mass index. This measurement is a ratio of weight in kilograms divided by body surface area in meters squared. In adults, obesity is defined as a BMI at or exceeding 30 kg/m2 .

table citation: CDC https://www.cdc.gov/obesity/basics/adult-defining.html

While the BMI is an easy tool used to screen for and diagnose obesity, it has limitations. BMI does not distinguish adipose (fat tissue) from muscle. For example, fit people with high muscle mass can have a high BMI since their body weight is higher due to muscle. Nor does it account for the differences in body shape or body fat between sexes, as females have a higher body fat percentage.

Common alternative measurements to the BMI for approximating body fat include⁴:

• Waist circumference

• Waist to height ratio

• Relative fat mass (an equation based on height, waist circumference, and sex)⁵

• Skinfold thickness, measured with calipers

• Bioelectrical impedance, a technique the requires special equipment to estimate the body water content

How Common Is Obesity?

In the United States, obesity is common, and rates have significantly increased over the past decades. According to the CDC, as of 2020, approximately 40% of adults have clinical obesity in the United States, compared with about 30% in 2000.²

Obesity is also becoming more common in children and adolescents, with nearly 20% of those aged 2 to 18 years having obesity, as defined by being above the 95th percentile for the age-BMI growth chart.⁶

Disparities in Obesity Rates

Obesity is common in the United States but does not affect all populations equally. Disparities in rates of obesity exist among racial and ethnic groups and vary by socioeconomic status and geography. Multiple causes contribute to these disparities, including social determinants of health. These include behaviors on diet and level of activity, neighborhood and community factors, including access to health care, and environments conducive to physical activity.

Obesity Disproportionately Affects Racial and Ethnic Groups

According to CDC data, rates of obesity in racial and ethnic groups are as follows:²

Non-Hispanic Black adults: 49.9%

Hispanic adults: 45.6%

Non-Hispanic White adults: 41.4%

Non-Hispanic Asian adults: 16.1%

Obesity rates also vary by education level and income; however, the relationships are not straightforward or generally applicable since rates are inconsistent across gender and racial and ethnic identity. For example, while most groups with college degrees had lower rates of obesity, this was not the case for college-educated non-Hispanic Black men, whose rates of obesity were higher than those who did not attain a college degree.⁷

Some sexual minority groups are also disproportionately affected by obesity. According to data from the Behavioral Risk Factor Surveillance System, those identifying as lesbian and bisexual had higher rates of obesity than those identifying as heterosexual.⁸

Obesity Causes and Risk Factors

Obesity in the U.S. is often blamed on the American diet and sedentary lifestyle, which certainly contribute to the high prevalence in the United States. However, the reality is more nuanced. There are many varied and complex causes that contribute to obesity:⁹

• Sedentary lifestyle, including lack of exercise and the rise of sedentary professions.¹⁰ Physical inactivity is one of several contributors to the observed socioeconomic disparities in obesity rates in those who do not have a reliable or safe space for regular exercise.

• Diet high in saturated fats, processed foods, and sweetened beverages

• Lack of sleep¹¹

• Longterm stress

• Medications like antipsychotics, antidepressants, corticosteroids, and insulin

• Health conditions, like polycystic ovarian syndrome (PCOS), Cushing syndrome, hypothyroidism

• Gastrointestinal Microbiome¹²

• Air pollution¹³¹⁴

• Genetic predisposition

Mortality Rates

Obesity is associated with several serious health conditions that are known to increase mortality, like high blood pressure, heart disease, and diabetes. So it's not surprising that obesity would lower survival. However. studies on mortality rates in obesity have been complicated by the fact that at the time of death, many of the people studied had lost weight due to severe illness.

One large, long-term study performed over 24 years attempted to account for this problem and showed that in those with obesity, the higher the BMI, the higher the mortality rates. Death from heart disease and cancer were each associated with obesity.¹⁵

Prevention and Treatment

Obesity is a serious and common problem in the United States due to various causes, not just limited to a sedentary lifestyle and diet. And while not all risk factors for obesity can be controlled, there are definite ways to achieve weight loss and improve the risk of some of the complications of obesity.

Healthy Lifestyle

The following lifestyle factors can help prevent and manage obesity:¹⁶

• Regular physical activity

• Healthy diet, eating less calorie-dense/nutrient-poor foods and avoiding sugar-sweetened drinks, saturated fats, and processed foods. The Mediterranean diet is a heart-healthy diet that has been shown to improve weight.¹⁷

• Adequate, restful sleep

• Stress management

If medications and/or health conditions are contributing to weight gain, see your healthcare provider for advice on possible alternative medications and treatment of other conditions.

Weight Loss Programs

Psychology and behavior plays a role in eating behavior and weight gain. These programs that include a healthcare provider can be effective. In addition, these programs may have a nutritionist, exercise expert, or psychologist, who can review your eating and exercise habits and give strategies and motivation for weight loss in an individual or group setting.¹⁶

Medication

Several prescription medications have been approved to treat obesity in the United States. They can work by suppressing appetite, reducing fat absorption, or increasing metabolism. Medications used for weight loss include the following:¹⁸

• Xenical (orlistat)

• Qsymia (phentermine/topiramate)

• Contrave (naltrexone/bupropion)

• GLP-1 (glucagon-like protein) agonists like Saxenda (liraglutide), Wegovy (semaglutide), and Zepbound (tirzepatide). Other formulations of this class of medication are used to treat diabetes.

Medications are not the first line of management for weight loss but can be prescribed in addition to lifestyle measures, especially when obesity-related conditions like diabetes, high blood pressure, and heart disease are present.¹⁸

Weight Loss Surgery

Weight loss surgery, also known as bariatric surgery, is an invasive but effective treatment for obesity. Several types of bariatric surgery exist. However, due to the risks involved, not everyone is a candidate for bariatric surgery, and it is reserved for the following:¹⁹

• Those with BMI over 40

• Those with BMI over 35 with serious conditions related to obesity

Summary

Obesity is common and has become more prevalent in the United States over the past years. Clinical obesity increases the risk of serious health conditions like heart disease, diabetes, and cancer. The body mass index is used to define and categorize types of obesity, but it is an imperfect measurement, particularly in certain groups of people. Lifestyle changes, medications, and bariatric surgery approaches may be used to prevent and treat obesity and its complications.