- 7 Primary Causes of Obesity
- Rising Obesity in the United States Is a Public Health Crisis
- Obesity and overweight
- What are obesity and overweight
- Facts about overweight and obesity
- What causes obesity and overweight?
- What are common health consequences of overweight and obesity?
- Facing a double burden of disease
- How can overweight and obesity be reduced?
- WHO response
- Obesity in America
- Obesity Statistics
- Children and Adolescents
- Is Obesity Epidemic?
- The Epidemic of Obesity
- Lifestyle trends
- Measuring overweight and obesity
- Health consequences
- Heart disease
- Cerebrovascular disease
- Additional consequences
- Economic impact
7 Primary Causes of Obesity
Americans are gaining weight, and obesity has become a national health threat. We can’t place the problem purely on self-control. Why has obesity become such a weighty issue?
Your daily meals are like a bank account: you take in calories (income) and spend them on physical activity (expense). When you take in more calories than you burn, you have a positive energy balance. While this would be a good thing for your bank account, it may not be a good thing for your weight. Of course, it is not simply a matter of addition and subtraction, and some people gain weight more readily than others. Several factors come into play.
Why Are We Packing On the Pounds?
Changes in our society and eating habits have contributed to the increase in obesity.
We eat differently.
- We consume too much sugar: 60% of adults drink at least 1 sugary drink a day.
- Foods higher in sugar, salt, and fat are widely marketed and advertised.
- It often costs more to eat healthy.
- Some people—especially those in lower-income, minority, and rural areas—do not have ready access to stores that sell healthy, affordable foods (eg, vegetables and fruit).
- Restaurants, fast-food chains, and vending machines often sell higher-calorie foods. School vending machines and cafeterias are no exception.
- Portion sizes, especially of less-healthful foods and beverages, have gotten bigger.
We do not get enough physical activity.
- Safe walking or biking routes may be limited, so we rely on our cars, even for short trips.
- Recreation centers and parks may not be easily accessible.
- Students do not get enough, or good enough, physical education.
- Most chores are now mechanized—gas or electricity powers the machines we use.
- Technology has made us sedentary.
We have become a nation of “couch potatoes.”
- We spend too much time in front of a screen—a lot of time watching TV or in front of the computer—and this is especially true for children. Children between the ages of 8 and 18 years spend 7.5 hours each day engaging in entertainment media—TV, computers, cell phones, movies, and video games—and about 4.5 of these hours are devoted to watching TV.
- Not only do these passive pursuits detract from time that could be spent on physical activity, we eat meals and have snacks around the TV, which does its share of promoting this habit through advertising of high-calorie, unhealthful foods.
Breastfeeding is stopped too soon.
- Breastfeeding protects children from becoming obese. However, although 75% of mothers do breastfeed, just 13% of infants rely on breast milk alone after 6 months.
Other factors exist that are mostly out of our control.
Heredity plays a role.
- Genetic conditions such as Prader-Willi syndrome, for example, are a direct cause of obesity.
- Scientists believe that a combination of certain genes and behavior may be needed to trigger obesity. A person’s genetic makeup may make him or her susceptible to obesity, but other factors are required to complete the picture.
- Certain disorders (Cushing’s disease and hypothyroidism, for example) can cause a person to gain weight.
- Some drugs (antidepressants, steroids, and diabetes medications, for example) can cause weight gain.
An individual’s behavior, socioeconomic status, culture, and environmental factors also contribute to overweight and obesity. In addition, hormones in the brain, the gastrointestinal tract, and in fat cells themselves influence his or her metabolism, eating habits, and, ultimately, weight.
Updated on: 08/16/18 Continue Reading Obesity and Health Consequences View Sources
Centers for Disease Control and Prevention. Vital Signs: Adult Obesity. Updated August 3, 2010. www.cdc.gov/vitalsigns/AdultObesity/#Whatcanbedone. Accessed March 20, 2015.
Centers for Disease Control and Prevention. Overweight and Obesity: Adult Obesity Facts. Updated September 9, 2014. www.cdc.gov/obesity/data/adult.html. Accessed March 20, 2015.
Centers for Disease Control and Prevention. Defining Overweight and Obesity. Reviewed April 27, 2012. www.cdc.gov/obesity/adult/defining.html. Accessed March 20, 2015.
Centers for Disease Control and Prevention. Overweight and Obesity. Causes and Consequences. Reviewed April 27, 2012. www.cdc.gov/obesity/adult/causes/index.html. Accessed March 20, 2015.
Apovian C, Korner J. Hormones and Obesity Fact Sheet. Hormone Health Network. March 2010. www.hormone.org. Accessed March 20, 2015.
Rising Obesity in the United States Is a Public Health Crisis
Obesity is a grave public health threat, more serious even than the opioid epidemic. It is linked to chronic diseases including type 2 diabetes, hyperlipidemia, high blood pressure, cardiovascular disease, and cancer. Obesity accounts for 18 percent of deaths among Americans ages 40 to 85, according to a 2013 study challenging the prevailing wisdom among scientists, which had placed the rate at around 5 percent. This means obesity is comparable to cigarette smoking as a public health hazard; smoking kills one of five Americans and is the leading preventable cause of death in the United States.
The obesity crisis may be less dramatic than the opioid epidemic now gripping the nation, but it is just as deadly. Opioids accounted for around two-thirds of the 64,000 deaths related to drug overdose in 2016. Excess body weight leading to cancer causes about 7 percent of cancer-related deaths, or 40,000 deaths each year. This number doesn’t include deaths from the many other medical conditions associated with obesity. Obese people are between 1.5 to 2.5 times more likely to die of heart disease than people with normal body mass indices (BMIs).
There are also substantial economic losses associated with obesity. The medical costs of prevention, diagnosis, and treatment are estimated at $147 billion in 2008 dollars. Reduced economic productivity adds to these losses.
Because rising obesity is attributed to an increase in caloric intake and a reduction in physical activity, many proposed solutions emphasize food and exercise. While such remedies may help in individual cases, policy solutions are almost certainly required to fight this alarming epidemic.
Despite the thriving U.S. weight-loss market (worth $66 billion in 2017), there is no evidence that diet-related programs will curb obesity. Numerous studies indicate that diets are not effective in controlling or reversing weight gain. In fact, 50 percent of dieters weighed more than 11 pounds over their starting weight five years after their diet, according to one study.
A comprehensive discussion of the policy solutions to obesity is beyond the scope of this piece, and the jury is still out on which policies — targeting sugar consumption through taxes on sugary food and beverages, regulating nutrition labels to make them more effective in informing consumers, and limiting the advertising and marketing of unhealthy food, particularly to children — might curb the epidemic.
Taxing potentially harmful food products has shown some promise, though it is a politically fraught approach. A small number of American cities, including Philadelphia, Boulder, Colo., and Berkeley, Calif., have begun taxing sugar-sweetened beverages. Early results show that an excise tax on sugary drinks led to a 21 percent drop in their consumption in Berkeley.
Berkeley is hardly the epicenter of the obesity problem in the U.S., as the map shows, but the intervention’s success offers hope for the rest of the country. A peer-reviewed modeling study based on the Berkeley experience estimated that if a national sugar-sweetened beverages tax were implemented, it would result in lower national consumption of these drinks and reduced adult and child BMIs. Whether such a policy could be replicated nationally remains uncertain.2
When it comes to nutrition labels, there’s almost no evidence that these have an effect on consumers’ dietary intake, body weight, and overall health.
Evidence suggests that advertising and marketing influences food preferences and choices among children. One study from the United Kingdom found that 8.7 percent of the sugar brought into the home was in food and drink that were advertised or sold at a discount. Although limits on advertising pose First Amendment challenges in the U.S., protecting children from aggressive advertising of sugary drinks and other unhealthy foods could have an impact on the childhood obesity epidemic.
One ray of hope from the most recent federal data is that youth obesity plateaued between 2005–06 and 2013–14. The study’s authors couldn’t explain why, but told the New York Times that “something different is happening with adults and youth.” Efforts to address childhood obesity are underway across the country: The Childhood Obesity Declines Project found that multilayered initiatives, supported by cross-sector partnerships, contributed to reductions in childhood obesity rates in four communities.
As we search for solutions at home, it’s worth noting that the obesity epidemic has leaped from our shores to the developed and even the developing world. Among OECD countries, Mexico has the second-highest rate of obesity (after the U.S.), followed closely by New Zealand and Hungary. Obesity is also on the rise in middle-income and poor countries: China, India, and Brazil are grappling with the epidemic.
Opiates can kill quickly and dramatically, but obesity kills just as surely. This epidemic deserves urgent attention. Providing affordable health care to Americans will prove increasingly difficult as weight gain continues to ravage the United States.
1 Obesity is defined as a body mass index (BMI) of 30 or more, and severe obesity is defined as a BMI of 40 or more.
2 The model simulated the 2015 U.S. population above the age of 2 at the baseline and followed them for 10 years until death, or age 100 years. As with all simulation models, this is a best estimate in the absence of direct evidence.
Obesity and overweight
What are obesity and overweight
Overweight and obesity are defined as abnormal or excessive fat accumulation that may impair health.
Body mass index (BMI) is a simple index of weight-for-height that is commonly used to classify overweight and obesity in adults. It is defined as a person’s weight in kilograms divided by the square of his height in meters (kg/m2).
For adults, WHO defines overweight and obesity as follows:
- overweight is a BMI greater than or equal to 25; and
- obesity is a BMI greater than or equal to 30.
BMI provides the most useful population-level measure of overweight and obesity as it is the same for both sexes and for all ages of adults. However, it should be considered a rough guide because it may not correspond to the same degree of fatness in different individuals.
For children, age needs to be considered when defining overweight and obesity.
Children under 5 years of age
For children under 5 years of age:
- overweight is weight-for-height greater than 2 standard deviations above WHO Child Growth Standards median; and
- obesity is weight-for-height greater than 3 standard deviations above the WHO Child Growth Standards median.
- Charts and tables: WHO child growth standards for children aged under 5 years
Children aged between 5–19 years
Overweight and obesity are defined as follows for children aged between 5–19 years:
- overweight is BMI-for-age greater than 1 standard deviation above the WHO Growth Reference median; and
- obesity is greater than 2 standard deviations above the WHO Growth Reference median.
- Charts and tables: WHO growth reference for children aged between 5–19 years
Facts about overweight and obesity
Some recent WHO global estimates follow.
- In 2016, more than 1.9 billion adults aged 18 years and older were overweight. Of these over 650 million adults were obese.
- In 2016, 39% of adults aged 18 years and over (39% of men and 40% of women) were overweight.
- Overall, about 13% of the world’s adult population (11% of men and 15% of women) were obese in 2016.
- The worldwide prevalence of obesity nearly tripled between 1975 and 2016.
In 2016, an estimated 41 million children under the age of 5 years were overweight or obese. Once considered a high-income country problem, overweight and obesity are now on the rise in low- and middle-income countries, particularly in urban settings. In Africa, the number of overweight children under 5 has increased by nearly 50 per cent since 2000. Nearly half of the children under 5 who were overweight or obese in 2016 lived in Asia.
Over 340 million children and adolescents aged 5-19 were overweight or obese in 2016.
The prevalence of overweight and obesity among children and adolescents aged 5-19 has risen dramatically from just 4% in 1975 to just over 18% in 2016. The rise has occurred similarly among both boys and girls: in 2016 18% of girls and 19% of boys were overweight.
While just under 1% of children and adolescents aged 5-19 were obese in 1975, more 124 million children and adolescents (6% of girls and 8% of boys) were obese in 2016.
Overweight and obesity are linked to more deaths worldwide than underweight. Globally there are more people who are obese than underweight – this occurs in every region except parts of sub-Saharan Africa and Asia.
What causes obesity and overweight?
The fundamental cause of obesity and overweight is an energy imbalance between calories consumed and calories expended. Globally, there has been:
- an increased intake of energy-dense foods that are high in fat; and
- an increase in physical inactivity due to the increasingly sedentary nature of many forms of work, changing modes of transportation, and increasing urbanization.
Changes in dietary and physical activity patterns are often the result of environmental and societal changes associated with development and lack of supportive policies in sectors such as health, agriculture, transport, urban planning, environment, food processing, distribution, marketing, and education.
What are common health consequences of overweight and obesity?
Raised BMI is a major risk factor for noncommunicable diseases such as:
- cardiovascular diseases (mainly heart disease and stroke), which were the leading cause of death in 2012;
- musculoskeletal disorders (especially osteoarthritis – a highly disabling degenerative disease of the joints);
- some cancers (including endometrial, breast, ovarian, prostate, liver, gallbladder, kidney, and colon).
The risk for these noncommunicable diseases increases, with increases in BMI.
Childhood obesity is associated with a higher chance of obesity, premature death and disability in adulthood. But in addition to increased future risks, obese children experience breathing difficulties, increased risk of fractures, hypertension, early markers of cardiovascular disease, insulin resistance and psychological effects.
Facing a double burden of disease
Many low- and middle-income countries are now facing a “double burden” of disease.
- While these countries continue to deal with the problems of infectious diseases and undernutrition, they are also experiencing a rapid upsurge in noncommunicable disease risk factors such as obesity and overweight, particularly in urban settings.
- It is not uncommon to find undernutrition and obesity co-existing within the same country, the same community and the same household.
Children in low- and middle-income countries are more vulnerable to inadequate pre-natal, infant, and young child nutrition. At the same time, these children are exposed to high-fat, high-sugar, high-salt, energy-dense, and micronutrient-poor foods, which tend to be lower in cost but also lower in nutrient quality. These dietary patterns, in conjunction with lower levels of physical activity, result in sharp increases in childhood obesity while undernutrition issues remain unsolved.
How can overweight and obesity be reduced?
Overweight and obesity, as well as their related noncommunicable diseases, are largely preventable. Supportive environments and communities are fundamental in shaping people’s choices, by making the choice of healthier foods and regular physical activity the easiest choice (the choice that is the most accessible, available and affordable), and therefore preventing overweight and obesity.
At the individual level, people can:
- limit energy intake from total fats and sugars;
- increase consumption of fruit and vegetables, as well as legumes, whole grains and nuts; and
- engage in regular physical activity (60 minutes a day for children and 150 minutes spread through the week for adults).
Individual responsibility can only have its full effect where people have access to a healthy lifestyle. Therefore, at the societal level it is important to support individuals in following the recommendations above, through sustained implementation of evidence based and population based policies that make regular physical activity and healthier dietary choices available, affordable and easily accessible to everyone, particularly to the poorest individuals. An example of such a policy is a tax on sugar sweetened beverages.
The food industry can play a significant role in promoting healthy diets by:
- reducing the fat, sugar and salt content of processed foods;
- ensuring that healthy and nutritious choices are available and affordable to all consumers;
- restricting marketing of foods high in sugars, salt and fats, especially those foods aimed at children and teenagers; and
- ensuring the availability of healthy food choices and supporting regular physical activity practice in the workplace.
Adopted by the World Health Assembly in 2004, the “WHO Global Strategy on Diet, Physical Activity and Health” describes the actions needed to support healthy diets and regular physical activity. The Strategy calls upon all stakeholders to take action at global, regional and local levels to improve diets and physical activity patterns at the population level.
The Political Declaration of the High Level Meeting of the United Nations General Assembly on the Prevention and Control of Noncommunicable Diseases of September 2011, recognizes the critical importance of reducing unhealthy diet and physical inactivity. The political declaration commits to advancing the implementation of the “WHO Global Strategy on Diet, Physical Activity and Health”, including, where appropriate, through the introduction of policies and actions aimed at promoting healthy diets and increasing physical activity in the entire population.
WHO has also developed the “Global Action Plan for the Prevention and Control of Noncommunicable Diseases 2013-2020” which aims to achieve the commitments of the UN Political Declaration on Noncommunicable diseases (NCDs) which was endorsed by Heads of State and Government in September 2011. The “Global Action Plan” will contribute to progress on 9 global NCD targets to be attained by 2025, including a 25% relative reduction in premature mortality from NCDs by 2025 and a halt in the rise of global obesity to match the rates of 2010.
The World Health Assembly welcomed the report of the Commission on Ending Childhood Obesity (2016) and its 6 recommendations to address the obesogenic environment and critical periods in the life course to tackle childhood obesity. The implementation plan to guide countries in taking action to implement the recommendations of the Commission was welcomed by the World Health Assembly in 2017.
Obesity in America
The United States has seen a dramatic increase in obesity in recent decades.
In the United States, nearly 35 percent of adults are obese, according to the Centers for Disease Control and Prevention (CDC).
Additionally, 18 percent of children ages 6 to 11 and 21 percent of adolescents ages 12 to 19 are also considered obese.
This is a dramatic increase over 1980, when only about 15 percent of adults, 7 percent of children, and 5 percent of adolescents were obese.
By definition, obese means having excessive body fat. It’s also often defined as having a body mass index (BMI) of 30 or higher.
Obesity is associated with some of the leading causes of preventable death, including heart disease, stroke, type 2 diabetes, and some types of cancer.
The CDC currently estimates that about 112,000 American deaths per year are associated with obesity.
The medical costs associated with obesity have been estimated at between $147 million and $210 million per year, or nearly 10 percent of all medical spending in America.
While the overall number of obese Americans has risen, some racial and ethnic groups are affected more than others:
- Among African-Americans, nearly 48 percent are obese.
- Among Hispanics, nearly 43 percent are obese.
- Among Caucasians, nearly 33 percent are obese.
- Among Asian-Americans, nearly 11 percent are obese.
Rates differ among age groups, as well:
- Nearly 40 percent of adults ages 40 to 59 are obese.
- About 35 percent of adults over age 60 are obese.
- About 30 percent of adults ages 20 to 39 are obese.
Rates vary by U.S. state, with Mississippi and West Virginia having the highest prevalence of obesity, at more than 35 percent of adults, according to the CDC.
Colorado and Hawaii have the lowest prevalence of adult obesity, at just over 21 percent, but no U.S. state has a prevalence of obesity that’s less than 20 percent of its adult population.
Children and Adolescents
Obesity in children and teens has negative health effects in both the short-term and long-term.
In the short term, obesity can lead to:
- Sleep apnea (brief interruptions in breathing during sleep)
- Social discrimination and low self-esteem
- Risk factors for cardiovascular disease, such as high cholesterol levels, high blood pressure, and high blood glucose levels
Possible longer-term effects include:
- Heart disease
- Type 2 diabetes
A number of organizations are attempting to help children lead healthier lives and to decrease the number of overweight and obese children and teens. Two of the larger programs are:
- Let’s Move, an initiative of Michelle Obama, which focuses on healthy eating, physical activity, and other behavioral steps that constitute a healthy lifestyle
- The Alliance for a Healthier Generation, founded by the American Heart Association and the Clinton Foundation, which attempts to build healthier school environments for students and staff by establishing school policies on food, physical and health education, and employee wellness programs
Is Obesity Epidemic?
The word “epidemic” is usually used to describe the rapid spread of an infectious disease among many people in a community.
Obesity is not generally considered an infectious disease (though ongoing research may change this perception), but its spread has been declared by many to have reached epidemic proportions.
There’s no question that obesity is widespread in America and in much of the world.
The global spread of obesity has been fueled in large part by the growing availability and popularity of the Western-style diet, which is characterized by foods with high contents of sugars, salt, and fat — particularly from processed foods and red meat.
Section One – Continued
OBESITY AND MORTALITY
According to the National Institutes of Health, obesity and overweight together are the second leading cause of preventable death in the United States, close behind tobacco use (3). An estimated 300,000 deaths per year are due to the obesity epidemic (57).
The results of two extensive studies examining obesity-attributable deaths in the United States were published in 1999. Allison, Fontaine, and Manson et al., reporting in the Journal of the American Medical Society, used data from a number of prospective cohort studies, including the Alameda Community Health Study, the Framingham Heart Study, the Tecumseh Community Health Study, the American Cancer Society’s Cancer Prevention Study I, the National Health and Nutrition Examination Survey I Epidemiologic Follow-up Study, and the Nurses’ Health Study, to estimate the number of deaths attributable to obesity in the United States on an annual basis (66). Their initial analyses, which examined deaths occurring among persons aged 18 and older in 1991, were adjusted only for age, sex, and smoking status. The weight categories used were overweight (BMI of 25-29.9), obese (BMI of 30-35), and severely obese (BMI >35).
Using data on all eligible subjects from all six studies, Allison et al. estimated that 280,184 obesity-attributable deaths occurred in the U.S. annually. When risk ratios calculated for nonsmokers and never-smokers were applied to the entire population (assuming these ratios to produce the best estimate for all subjects, regardless of smoking status, i.e., that obesity would exert the same deleterious effects across all smoking categories), the mean estimate for deaths due to obesity was 324,940.
Additional analyses were performed controlling for prevalent chronic disease at baseline using data from the CPS1 and NHS. After controlling for preexisting disease, the mean annual number of obesity-attributable deaths was estimated to be 374,239 (330,324 based on CPS1 data and 418,154 based on NHS data).
Calle, Thun et al. selected their study subjects from over one million participants in the Cancer Prevention Study II, a prospective study of mortality among adults in the U.S. begun by the American Cancer Society in 1982 (67). Calle et al. examined deaths occurring between 1982 and 1996 among four cohorts: (1) current or former smokers with no history of disease3, (2) current or former smokers with a history of disease, (3) nonsmokers with no history of disease, and (4) nonsmokers with a history of disease. Weight categories were normal range (18.5-24.9), grade 1 overweight (25.0-29.9), grade 2 overweight (30.0-39.9), and grade 3 overweight (40.0+). All cause mortality, cardiovascular disease (CVD) mortality, and cancer mortality were examined.
The lowest mortality rates from all causes were found among study subjects having a BMI of between 23.5-24.9 for men and 22.0-23.4 for women. The risk of mortality increased with increasing BMI at all ages and for all categories of death. The strongest association between obesity and death from all causes was found among study subjects who had never smoked and had no history of disease, with the highest rates among the heaviest men and women, i.e., those with a BMI of 40+. The relative risk (RR) was 2.68 among men and 1.89 among women, compared with the reference groups (a BMI of 23.5-24.9 among men and 22.0-23.4 among women). This association was stronger in whites than among blacks.
Obesity was associated with higher mortality rates for both cardiovascular disease and cancer. BMI was most strongly associated with cardiovascular disease mortality among men (RR=2.90), but significantly increased risks of CVD death were found at all BMIs of greater than 25.0 in women and 26.5 in men. The findings showed an increase of 40% to 80% in risk of dying from cancer among both men and women in the highest weight categories.
Calle et al.’s study supports the need for further research to ascertain the differences in the effect of obesity on mortality among the black population, especially among black women. Their data also support the use of a single recommended range of body weight throughout life.
An earlier (1995) study by Manson, Willett, and Stamfer et al. examined data from the Nurses’ Health Study, looking at 4,726 deaths occurring from 1976 through 1992, 881 from cardiovascular disease, 2,586 from cancer, and 1,259 from other causes (68). A direct association was observed between BMI and mortality among women who had never smoked. Using a BMI of <19.0 as the reference group (relative risk =1.0), women with BMIs of 19.0-21.9 and 22.0-24.9 had a RR of 1.2; women with a BMI of 25.0-26.9 had a RR of 1.3; women with a BMI of 27.0-28.9 had a RR of 1.6; those with a BMI of 29.0-31.9 had a RR of 2.1; and those with a BMI of >32.0 had a RR of 2.2. Among never smokers, women with a BMI of >32 had a RR of 4.1 of dying from cardiovascular disease and a RR of 2.1 of dying from cancer.
3Cancer (excluding nonmelanoma skin cancer), heart disease, stroke, respiratory disease, current illness of any type, or a weight loss of at least 10 pounds in the preceding year.
Continue with Section One:
- The Economic Costs of Obesity
- Treatment of Obesity
- Top of Page
The Epidemic of Obesity
As the obesity epidemic spreads, concern about the significant health and economic consequences has also grown. Obesity has been linked to a variety of chronic diseases, almost 300,000 deaths each year, and $117 billion in direct and indirect annual costs in the United States alone. In this article we review the recent trends in overweight and obesity, summarize the lifestyle factors that influence the increasing prevalence of obesity, and discuss the health and economic impact of the obesity epidemic.
THE UNITED STATES is experiencing an epidemic of overweight and obesity. The prevalence of excess weight is increasing rapidly across the country, and today close to 65% of the adult population is overweight or obese (1). Comparing the period 1976–1980 (2) with 1999–2000 (1), the prevalence of overweight has increased by 40% (from 46.0% to 64.5%) and the prevalence of obesity (BMI ≥ 30 kg/m2) has risen by 110% (from 14.5% to 30.5%).
We are also witnessing an alarming increase in weight among our youth. More than 10% of 2- to 5-yr-olds and 15% of 6- to 19-yr-olds are overweight (BMI ≥ 95th percentile for age and gender) (3). This represents a near-doubling of overweight children and a near-tripling of overweight adolescents over the last two decades (4). Whereas some segments of the population are more likely to be overweight or obese than others, people of all ages, races, ethnicities, socioeconomic levels, and geographic areas are experiencing a substantial increase in weight (4).
International data indicate that the epidemic is not isolated to the United States but is in fact a global health problem (5, 6). The prevalence of obesity is rising in other developed and affluent countries and is now spreading to less affluent countries (6).
Overweight and obesity result from the interaction of many factors, including genetic, metabolic, behavioral, and environmental influences. The rapidity with which obesity is increasing suggests that behavioral and environmental influences, rather than biological changes, have fueled the epidemic. Increasing energy consumption, decreasing energy expenditure, or a combination of both has led to a positive energy balance and a marked increase in weight in our society.
Over time, changes in our eating habits and activity levels have occurred, but the specific details of these complex behavior changes are not well understood. In evaluating caloric intake, the data from large national surveys have shown mixed results (7). For example, data from the National Health and Nutrition Examination Survey suggest that average energy intake increased between 1971 and 2000 (8). However, Popkin et al. (9) analyzed data from the Nationwide Food Consumption Survey (1965 and 1977–1978) and the Continuing Survey of Food Intake by Individuals (1989–1991 and 1994–1996) and did not find a large difference in caloric intake in 1994–1996 compared to 1965.
Outside national surveys, ecological data seem to support the idea that energy intake has increased (7). Despite the fact that there has been an increase in availability and consumption of lower-fat food items over time, a number of trends have been described that could contribute to an increased energy balance and the observed rise in obesity: higher per capita energy availability (10), increased percentage of food consumed outside the home including fast foods (7, 11), greater consumption of soft drinks (11–13), and larger portion sizes (7, 13).
The inconsistent data on energy intake suggest that rising levels of obesity may be more closely related to changes in energy expenditure. As with energy intake, competing influences exist. For example, the number of health clubs, recreational facilities, and homes with exercise equipment has grown (14). However, sedentary activities, such as television watching and videogame playing, have also increased. Of note, television viewing is associated with greater weight in children and adults (15), but it is unclear whether this relationship is due more to a corresponding increase in food consumption or a decrease in physical activity (14). Overall, it appears that levels of leisure-time activity have not changed significantly (16).
What seems to have changed, however, is the level of activity required for work and daily living (17), although this has not yet been well documented. With advances in technology, there has been a greatly reduced dependence on walking and cycling for transportation. Household physical activity has likely decreased due to labor-saving devices. Occupational energy requirements have also dropped as mechanized labor aids have become available, and in general, jobs have become more sedentary.
Today 60% of the U.S. population does not participate in regular physical activity, and 25% are almost entirely sedentary (18). In addition, physical activity in schools has declined, and almost half of young Americans between the ages of 12 and 21 yr are not vigorously active on a routine basis (18).
Although the complexities of this relationship are not yet fully understood, the end result is quite clear: the imbalance of energy intake and energy expenditure has resulted in an epidemic of overweight and obesity across the United States.
Measuring overweight and obesity
As the prevalence of overweight and obesity continues to increase, efforts have been made to quantify this weight change in individuals and in the population. Because fat is stored throughout the body, it cannot be measured directly. Body weight itself can provide an indication of fat stores, but because body build and composition are extremely variable, there is no ideal body weight. Instead, other measurements are often used to estimate body fat and better quantify health risk. These include BMI, waist circumference, waist/hip ratio, skin-fold thickness, and bioimpedance. Although these measurements cannot capture all the variables that impact risk, they can be used as tools to estimate risk.
The measurement used most often to quantify body fat is BMI. It is relatively easy to calculate (weight in kilograms divided by the square of the height in meters); it has defined risk categories (overweight, BMI ≥ 25 kg/m2; and obese, BMI ≥ 30 kg/m2), and it is closely correlated with body fat in most people. It is not a perfect measure, however. BMI does not distinguish between fat mass and lean mass and, therefore, does not provide an accurate indication of body fat in extremely muscular individuals or people who have lost significant muscle mass. In addition, BMI may not be a sensitive indicator of the health risks associated with moderate weight gain (10–20 lb) in individuals that fall within the normal BMI range. Despite these limitations, BMI can be a reliable and valid measure for identifying adults at increased risk of overweight- and obesity-related morbidity and mortality (19).
Even small increases in weight across a population can have a devastating impact on public health. Close to 300,000 deaths each year in the United States may be attributable to obesity (20), making obesity the second leading cause of preventable death in this country (21). Excess weight increases the risk of multiple conditions, including cardiovascular disease, type 2 diabetes, cancer, and premature death (4). The adverse health consequences occur not only in individuals who are in the overweight and obese categories, but disease risk also starts to increase even for those at the upper end of the normal range (BMI 22.0–24.9) (22).
Although there are a multitude of negative consequences associated with excess weight, many may be reversible with weight loss. For example, randomized trials have shown that weight loss leads to a reduction in blood pressure, better glucose tolerance, and an improved lipid profile (21). The U.S. Preventive Services Task Force has concluded that these improvements in intermediate outcomes provide indirect evidence of the health benefits achievable with modest weight reduction (19).
A large variety of studies have linked obesity to an increased risk of heart disease, and it has been estimated that 20–30% of cardiovascular disease (CVD) mortality may be attributable to excess body weight (23). This is especially significant given that heart disease is the most common cause of death in the United States, killing more than 700,000 Americans each year (24). Men and women who are overweight or obese may be 2 to 3 times more likely than their leaner peers to develop CVD (25, 26), and they are also more likely to die from it (23). Moreover, excess weight early in life is predictive of coronary heart disease mortality. Overweight adolescents may be more than twice as likely as their lean peers to die from coronary heart disease during adulthood (27).
Among men and women, hypertension is one of the most common conditions related to overweight and obesity (28). The diagnosis and treatment of hypertension come with enormous personal and financial costs, and complications include an increased risk of CVD, aortic dissection, renal damage, and cerebrovascular disease. In terms of its association with excess weight, there is a strong linear relation between BMI and blood pressure, and both weight (29–31) and weight gain (32, 33) are positively associated with the development of hypertension. For example, compared with leaner women, overweight women may be almost 3 times more likely and obese women nearly 6 times more likely to develop hypertension (29).
More than 18 million people in the United States have type 2 diabetes (34), which is the sixth leading cause of death in this country (24). Complications of diabetes include blindness, kidney disease, heart disease, stroke, peripheral vascular disease, and neuropathy. Using data from the Nurses Health Study (35), it was estimated that as much as 80% of type 2 diabetes could be attributed to the combined effect of inactivity and overweight/obesity (personal communication, Hu F.B., January 2001). There is a strong linear relationship between BMI and risk of type 2 diabetes mellitus, and obese individuals have almost 10 times the risk of diabetes, compared with their nonobese peers (36, 37). Independent of BMI, weight gain, waist circumference, and waist/hip ratio also strongly correlate with diabetes risk (38–42).
Excess weight has been linked to a variety of cancers. The International Agency for Research on Cancer has estimated that overweight and obesity cause 9% of postmenopausal breast cancer, 11% of colon cancer, 25% of renal cancer, 37% of esophageal cancer, and 39% of endometrial cancer (5). Calle et al. found that obesity was associated with a higher risk of death from 14 cancers (esophagus, colon and rectum, liver, gallbladder, pancreas, kidney, non-Hodgkin lymphoma, multiple myeloma, stomach, prostate, breast, uterus, cervix, and ovary), and it was estimated that overweight and obesity may account for 14% of all cancer deaths in men and 20% in women (42A ).
Stroke is the third leading cause of death in the United States (24) and a leading cause of significant, long-term disability. Various measures of obesity have been associated with an increased risk of cerebrovascular disease in men and women. For example, Rexrode et al. (43) reported that the risk of ischemic stroke increased with BMI, and obese women had approximately twice the risk as lean women. In men, associations between stroke and both BMI (22) and waist/hip ratio (43A ) have been reported.
Gallstones are fairly common, and whereas many are asymptomatic, they can cause pain and inflammation and often lead to treatment with laparoscopic cholecystectomy. Although gallstones do form in lean adults, the relationship between weight and gallstone formation is very strong. Compared with women in the healthy weight range, overweight women have close to twice the risk of developing gallstones, and obese women have 2.5–3 times the risk. Gallstones are more common in women; however, similar trends of increased risk with higher BMI have also been seen in men (22).
More than 20 million people in the United States have osteoarthritis (44). This condition, characterized by the degeneration of the joint cartilage, can cause severe pain and functional limitations. It is a leading cause of disability and also the most common reason for joint replacement surgery. Compared with their leaner peers, overweight adults are at increased risk of developing osteoarthritis of the knee (45) and are more than twice as likely to develop osteoarthritis in the hip (45). Overweight and obesity are also associated with an increased risk of knee and hip replacement surgery (46).
In addition to the diseases discussed above, overweight and obesity also increase the risk of a large variety of other conditions, including dyslipidemia, sleep apnea, asthma (4), cataracts (47–49), benign prostatic hypertrophy (50), menstrual irregularities, pregnancy complications, depression, and social discrimination (4). Obesity also negatively affects physical functioning, vitality (51), and general quality of life (52).
Excess weight not only causes widespread health effects, but it also results in a tremendous economic burden. Assessing this economic cost is an additional method of summarizing the broad impact of the epidemic on society. It is estimated that obesity costs the United States $117 billion each year (4). This estimate includes both direct costs (related to diagnosis and treatment of illness, including doctor visits, medications, hospitalizations, and nursing home stays) and indirect costs (resulting from lost wages and productivity due to illness or premature death) (4, 53).
The true cost of the current epidemic of overweight and obesity, however, is likely much higher than the $117 billion estimate. The estimate is based on the costs of obesity and does not fully address the costs related to those who are overweight but not obese. It also does not take into account other significant and costly conditions associated with obesity, such as reduced physical functioning, sleep apnea, pregnancy complications, and cataracts. Using a conservative approach, Thompson et al. (54) estimated that the excess health care costs linked to obesity were nearly as high as those associated with smoking.
The prevention and treatment of excess weight is critical for the health of both individuals and our society. Health care providers can play an important role in monitoring patients’ weight and assisting with diet and physical activity counseling. The U.S. Preventive Services Task Force recommends that clinicians screen patients for obesity and offer intensive counseling and behavioral interventions (19). All patients should be encouraged to maintain a healthy weight by eating a nutritious diet and exercising regularly to balance energy intake and energy expenditure. Individuals who are overweight should be assisted in losing weight gradually with a focus on long-term weight loss and maintenance. A variety of approaches can be effective in treating excess weight, and detailed guidelines have been created for providers to help patients with weight management (21).
Lifestyle interventions have proven effective in preventing and treating obesity (21, 55) and its health consequences (56). However, to be most successful and sustain positive change over time, individuals’ efforts must be facilitated and supported by the larger physical environment. With this aim, a variety of resources have been developed to address the issues of overweight and obesity at the community and population levels (57, 58). Multilevel interventions are needed if we are to stem the epidemic and prevent the growing negative consequences of overweight and obesity.
Body mass index;
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