Obesity

Obesity is a chronic disease affecting millions of people worldwide, characterized by excessive body fat that can harm health and quality of life. It goes beyond appearance, involving complex interactions between genetics, behavior, environment, and metabolism, and requires comprehensive, long-term management strategies.

Table of contents

• What is obesity?
• How common is obesity?
• Classification and measurement
• Causes and risk factors
• Health complications
• Diagnosis
• Treatment approaches
• Prevention

What is obesity?

Obesity is a chronic disease involving excessive body fat accumulation that presents a risk to health^[1][2]. It is not simply a cosmetic concern but a complex medical condition that affects overall health and quality of life^[1][3]. The condition develops over time and is characterized by abnormal or excessive fat accumulation or distribution^[2].

Obesity is more than just weighing too much. While being overweight means your weight is greater than what’s considered healthy for your height, obesity specifically refers to having too much body fat^[6]. The disease results from a mixture of behavioral, environmental, and genetic factors—not just from lifestyle choices^[17].

As a chronic disease, obesity requires lifelong care and management^[1][13]. The condition affects virtually every system in the body and is associated with a wide range of complications^[5]. Understanding that obesity is a disease helps remove stigma and emphasizes the need for comprehensive medical treatment rather than simply blaming individuals for their weight.

How common is obesity?

Obesity has become a major global health challenge. In 2022, one in eight people in the world were living with obesity^[7]. Worldwide adult obesity has more than doubled since 1990, while adolescent obesity has increased four-fold^[2][7].

The numbers are particularly striking in some regions. In the United States, obesity affects more than 2 in 5 adults (41.9% during 2017–March 2020)^[4]. This means that more than 100 million adults in the U.S. have obesity^[4]. The prevalence of severe obesity (an advanced form of the disease) affects 9.2% of U.S. adults, or more than 22 million people^[4].

Once considered a problem only in high-income countries, today some middle-income countries have among the highest rates of overweight and obesity worldwide^[2]. More people are now obese than underweight in every region except the South-East Asia Region^[2].

Obesity does not affect all groups equally. In the United States, non-Hispanic Black adults have the highest obesity prevalence at 49.9%, followed by Hispanic adults at 45.6%, non-Hispanic White adults at 41.4%, and non-Hispanic Asian adults at 16.1%^[4]. Education level also plays a role—obesity prevalence is highest among adults with a high school diploma or some college education (46.4%)^[4].

Classification and measurement

Healthcare providers use several methods to identify and classify obesity. The most common tool is body mass index, or BMI, which measures average body weight against average body height^[1][3]. To calculate BMI, multiply weight in pounds by 703, divide by height in inches, and then divide again by height in inches. Alternatively, divide weight in kilograms by height in meters squared^[3].

For adults, a BMI of 25 or greater is considered overweight, and a BMI over 30 is classified as obesity^[2][7]. Healthcare providers further classify obesity into three classes:

• Class I obesity: BMI 30 to less than 35 kg/m²
• Class II obesity: BMI 35 to less than 40 kg/m²
• Class III obesity: BMI 40 kg/m² or higher^[1]

While BMI is useful for screening, it has limitations. BMI doesn’t directly measure body fat and may not accurately predict health risks for everyone^[3][13]. For example, muscular athletes may have a BMI in the obesity category even though they don’t have excess body fat. Conversely, older persons who have lost muscle may have normal BMI but still have too much body fat^[3]. Social determinants, race, ethnicity, and age may also modify the risk associated with a given BMI^[13].

Another important measurement is waist circumference, which indicates where you carry extra weight^[1][3]. A waist circumference of more than 35 inches in females or 40 inches in males can indicate higher risk for cardiovascular disease (diseases of the heart and blood vessels) or Type 2 diabetes^[1]. Fat stored around the waist, sometimes called visceral fat or abdominal fat, may increase disease risk more than fat stored in other areas^[9].

Causes and risk factors

Obesity develops when you consume more calories than your body uses over time^[1][6]. However, the condition is far more complex than simply eating too much. Many factors contribute to obesity, and these factors interact with each other in complicated ways.

Genetics play a significant role. Research shows people with obesity often carry specific genes that affect appetite and how the body stores and uses fat^[1]. Obesity often results from inherited, physiological, and environmental factors, combined with diet, physical activity, and exercise choices^[3].

Eating habits contribute to obesity development. Consuming more calories than your body needs, eating ultra-processed foods, foods and drinks high in sugar, and foods with high amounts of saturated fat can lead to weight gain^[1]. As global diets have changed in recent decades, there has been an increase in consumption of energy-dense foods high in fat and free sugars^[2].

Physical inactivity is another major factor. High amounts of screen time—watching TV, playing video games, or spending time on mobile phones or laptops—cuts into time available for physical activity^[1]. There has also been a decrease in physical activity due to changing work patterns, more access to transportation, and increased urbanization^[2].

Other important factors include:

• Lack of sleep—missing out on at least seven hours of sleep can affect hormones that control hunger^[1]
• Stress—the brain and body react to stress by making hormones like cortisol (a hormone that helps manage stress) that affect hunger, leading to eating high-calorie comfort foods^[1]
• Certain medications—antidepressants, steroids, anti-seizure medications, diabetes medications, and beta-blockers can contribute to weight gain^[1]
• Underlying health conditions—diseases like metabolic syndrome (a cluster of conditions that increase disease risk) and polycystic ovary syndrome (a hormonal disorder affecting women) can cause weight gain^[1]
• Mental health issues—anxiety and depression can lead to eating high-calorie foods that activate pleasure centers in the brain^[1]
• Disability—adults and children with physical and learning disabilities face higher obesity risk due to physical limitations and lack of adequate specialized education and resources^[1]

Health complications

Obesity increases the risk of many serious diseases and health problems. In 2019, an estimated 5 million deaths from noncommunicable diseases (chronic diseases not passed from person to person) were caused by higher-than-optimal BMI^[2]. Obesity accounts for nearly $173 billion in medical expenditures in 2019 dollars in the United States^[4].

Cardiovascular complications are among the most serious. Obesity is a major risk factor for cardiovascular diseases such as heart disease and stroke, which are leading causes of death worldwide^[2][3]. Many adults with obesity have high blood pressure, a key risk factor for heart disease—58% of U.S. adults with obesity have high blood pressure^[4].

Obesity strongly increases the risk of Type 2 diabetes. Approximately 23% of U.S. adults with obesity have diabetes^[4]. Being overweight can also lead to diabetes-related complications, including blindness, limb amputations, and the need for dialysis^[2].

Other significant complications include:

• High cholesterol
• Liver disease
• Sleep apnea (a condition where breathing repeatedly stops and starts during sleep)
• Osteoarthritis (a joint disease causing pain and stiffness)
• Certain cancers, including endometrial, breast, ovarian, prostate, liver, gallbladder, kidney, and colon cancers^[2][3]
• Depression and other mental health conditions
• Pregnancy problems and fertility issues^[6]

The risk of these noncommunicable diseases increases even when a person is only slightly overweight and grows more serious as BMI climbs^[2]. In children, obesity is associated with a wide range of serious health complications and an increased risk of premature onset of related illnesses^[2].

Diagnosis

To diagnose obesity, healthcare providers perform several assessments. The process typically begins with taking a detailed health history^[9]. Your provider may review your weight history, previous weight-loss efforts, physical activity and exercise habits, eating patterns, and appetite control^[1][9]. They may also ask about other health conditions you have, medicines you take, stress levels, and family health history^[9].

A general physical examination follows, which includes measuring height, checking vital signs such as heart rate, blood pressure, and temperature, listening to the heart and lungs, and examining the abdomen^[1][9].

Healthcare providers calculate BMI to determine obesity classification and check waist circumference to assess fat distribution^[1][9]. These measurements should be checked at least once a year to help pinpoint overall health risks and determine appropriate treatments^[9].

Blood tests and other imaging tests may be ordered to check for known health problems and screen for other weight-related diseases and conditions^[1][6]. If you have underlying problems associated with obesity, such as high blood pressure, diabetes, or sleep apnea, your provider may recommend further tests or specific treatment, or refer you to a specialist^[14].

Treatment approaches

Treatment of obesity should not focus solely on weight loss but should adopt a holistic approach that includes preventing or improving complications, enhancing mental well-being, physical fitness, social functioning, and overall health and quality of life^[15].

The foundation of obesity treatment involves comprehensive lifestyle management—changes to diet, physical activity, and behavior—combined with long-term healthy habits^[1][12]. Healthcare professionals often describe obesity management using four pillars: nutrition therapy, physical activity, behavioral modification, and medical interventions^[11].

Lifestyle changes

Healthcare providers typically recommend adopting lifelong healthy lifestyle changes as the first approach^[10][23]. These changes should include self-monitoring of caloric intake and physical activity, goal setting, stimulus control, non-food rewards, and relapse prevention^[12].

For nutrition therapy, the goal is to create a negative caloric balance—using more calories than you consume—to achieve and sustain a healthy weight^[11]. Most people are advised to reduce energy intake by 600 calories a day to lose weight at a safe and sustainable rate of 0.5 to 1 kilogram per week^[14]. This typically means swapping unhealthy and high-energy food choices for healthier options, including plenty of fruits and vegetables, whole grains, and limiting foods high in sugar and fat^[14].

Physical activity increases metabolism and helps the body burn calories efficiently. It also aids in developing lean muscle mass, which contributes to fat burning^[11]. Most guidelines recommend at least 150 minutes per week of moderate-intensity aerobic physical activity, such as brisk walking or cycling^[10].

Behavioral modification addresses the psychological and emotional needs that contribute to obesity^[11]. Various techniques such as cognitive-behavioral therapy, mindfulness, and goal setting can help individuals develop healthier habits and sustain long-term weight management^[11].

Weight management programs

Healthcare providers may refer you to a specialist or a healthcare team trained in weight management^[10]. Safe and successful weight-loss programs typically include 14 or more weight-loss counseling sessions conducted over 6 months, an eating plan based on your body’s needs, at least 150 minutes per week of moderate-intensity physical activity, daily monitoring of food intake and physical activity, and regular feedback and support from specialists^[10].

Even modest weight loss can significantly improve health. Losing 5% to 10% of body weight can improve or prevent health problems associated with obesity^[3][10][23]. If you weigh 200 pounds, this means losing 10 to 20 pounds^[6].

Medications

When lifestyle changes alone are not sufficient, healthcare providers may recommend anti-obesity medications (AOMs) as part of comprehensive treatment^[11][15]. These medications work alongside lifestyle interventions to help manage eating behaviors and slow weight gain or regain^[11].

Several medications are now available for treating obesity, with varying effectiveness and modes of action^[15]. The choice of medication should be personalized based on individual patient characteristics and health conditions^[15]. Medications offer the potential to improve health and quality of life for patients with overweight or obesity^[11].

Surgery and procedures

For people with severe obesity or serious obesity-related health problems who have not been able to lose enough weight through other methods, bariatric (weight-loss) surgery or endoscopic procedures may be options^[6][10]. Bariatric surgery is the most effective intervention for patients with severe obesity^[12].

Well-performed bariatric surgery in carefully selected patients, carried out with good multidisciplinary support, substantially reduces the morbidities associated with severe obesity^[12]. Studies comparing patients with obesity who were treated with bariatric surgery with those who were not found the surgery to be associated with reduced coronary artery disease risk^[12].

Prevention

Many of the causes of overweight and obesity are preventable and reversible^[2]. Prevention requires organizations and people to work together to create communities, environments, and systems that support healthy, active lifestyles for all^[16].

At the individual level, you can adopt healthy lifestyle changes including eating a healthy, balanced diet and doing regular physical activity^[14]. A healthy diet should consist of plenty of fruits and vegetables, meals based on starchy foods (ideally whole grain varieties), some milk and dairy products, some protein sources, and only small amounts of foods and drinks high in fat and sugar^[14].

Communities can support obesity prevention by designing environments that connect sidewalks, bicycle routes, and public transportation with homes, schools, parks, and workplaces to increase physical activity^[16]. Other strategies include expanding programs that make healthy foods more available, promoting nutrition guidelines in worksites and community organizations, and implementing policies that support breastfeeding^[16].

Governments support prevention through programs that help families access affordable, nutritious foods, funding initiatives that promote healthy eating and physical activity, and developing guidelines on dietary patterns and amounts of physical activity needed for good health^[16].

Importantly, bias and stigmatization directed at people with obesity contribute to poor health and impair treatment^[13]. Healthcare providers and others should use respectful, non-stigmatizing, person-first language in all weight-related discussions^[16]. Understanding obesity as a disease rather than a personal failing is essential for effective prevention and treatment.