Causes of Obesity Epidemic

Overweight and obesity are caused by a complex array of genetic, metabolic, and behavioral interactions across a number of relevant social, environmental and policy contexts that influence eating and physical activity. The general consensus of obesity experts and researchers is that humans evolved to live in a very different environment than that in which they find themselves today.

For hundreds of thousands of years, food was scarce and humans needed to work hard physically to survive. Because famine was not uncommon, there was biological pressure and survival advantage to be able to store energy as fat for the lean times. Unfortunately, there are parts of the world where famine still is commonplace. But for most of the Western world, food is now abundant, cheap and very available, while very little physical activity is required in the typical course of daily living. Over the past three decades, increases in the proportion of meals eaten outside of the home, parental working hours, television and other media use, changes in marketing patterns and the school food environment have exacerbated the health effects of this historic shift in living conditions. The world has become an adverse environment for maintaining healthy body weight.

The profound increases in overweight and obesity rates seen in NYS and U.S. children and adults have also been seen internationally, both in developed and in developing countries. The rapidly increasing prevalence of obesity, with its associated adverse health, social and economic consequences, calls for immediate action based on the best available evidence as opposed to waiting for the best possible evidence (IOM, 2004). As we move forward, however, continued evaluation will be needed to assess the impacts of interventions and changes in policies and legislation.

Prevalence

Overweight and obesity are relative and span a continuum. Prevalence rates, however, require and depend on the definitions used. The most common and currently recommended definitions of overweight and obesity are based on a ratio of weight to height called Body Mass Index (BMI) (Table 1).

Table 1. Classifications for weight status based on Body Mass Index (BMI)

Source: NIH Publication no. 98-4083. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report. NHLBI (National Heart, Lung, and Blood Institute); 1998.

Experts at the CDC have been reluctant to classify children and teens as obese, suggesting instead that the terms “at-risk of overweight” and “overweight” be used because the ratios reflect measures of weight, not fat. They also raised concerns about possibly labeling children. The Institute of Medicine’s (IOM) report “Preventing Childhood Obesity” (2004), however, argues that “childhood obesity” is a stronger term because it conveys a better sense of health risks than does “childhood overweight.” BMI, however, is more highly correlated with body fat (National Research Council 1989), and associated with increased risk of hypertension, dyslipidemia, glucose intolerance, type 2 diabetes and arthritis in children and teens. In adults, the BMI cut points of 25 kg/m2 (which is approximately 10% above ideal body weight) and 30 kg/m 2 are based on epidemiologic data showing increasing morbidity (cardiovascular disease, diabetes, cancer, arthritis and disability) and mortality at a BMI greater than 25 kg/m 2, and even greater increases in risk for individuals with a BMI above 30 kg/m 2 (NHLBI, 1998).

The increased overweight and obesity prevalence among adult New Yorkers is similar to that seen among adults in the U.S. Based on self-reported height and weight, the proportion of NY adults who are either overweight or obese (i.e., BMI greater than 25 kg/m 2) increased 36%, from 42% to 57% between 1990 and 2002 respectively. During this same 13-year time period, the proportion of NY adults who would be classified as obese (i.e., BMI greater than 30 kg/m 2) more than doubled, increasing from 10% to 21% (Figure 1).

Figure 1: Trends in overweight and obesity among New York State adults

Source: 1990-2003 Behavioral Risk Factor Surveillance System (BRFSS)

The prevalence rates of obesity in NYS were comparable to the national rates in 2001 based on self-reported height and weight (20.9% vs. 20.3% respectively) (BRFSS, 2001).

Figure 2: Obesity among New York adults by locality

Sources: NYS, BRFSS 2003, age-adjusted to the 2000 U.S. population, based on self-reported height and weight. US- NHANES, 1999-2002, J Am Med Assn 2004;291:2847-2850.

Prevalence rates are lowest in the borough of Manhattan, in New York City(10% to 14%) and highest (25% or higher) in Orleans, Genesee, St. Lawrence, Jefferson, Lewis, Oswego, and Oneida counties of upstate NY (Figure 2). Hispanics have the highest prevalence of overweight (46%) of any ethnic group in NYS, while Blacks have the highest prevalence of obesity (30%). The prevalence of overweight and obesity in men is higher than women (65% vs. 49% respectively). However, the prevalence of obesity is higher among women compared to men (19% vs. 16% respectively). Based on measured height and weight (NHANES 1999-2004) the percentage of U.S. adults who are obese (30.4%) is more than double the Healthy People 2010 target level of 15% (Figure 3).

Obesity rates based on self-reported height and weight data (BRFSS) for NYS and the U.S. also exceed the target level. The percentages of adults at a healthy weight (i.e., BMI between 18.5 kg/m 2 and 24.9 kg/m 2) are 33% based on measured data for U.S. adults, and 43%, based on self-reported height and weight for NYS adults. These rates are much lower than the Healthy People 2010 target of 60% (Figure 4). Figure 3: Proportion of adults aged 20 years and older who are identified as obese (HP 2010 Objective 19-2)

Sources: NYS, BRFSS 2003, age-adjusted to the 2000 U.S. population, based on self-reported height and weight. US- NHANES, 1999-2002, J Am Med Assn 2004;291:2847-2850.

Figure 4: Proportion of adults, ages 20 years and older, at a healthy weight* (HP Objective 19-1)

It should be noted that data based on measured height and weight are approximately 50% higher than rates based on self-reported data. In NHANES 1999-2000, obesity prevalence did not differ across racial/ethnic categories for adult men. But among adult women, non-Hispanic Black women had the highest obesity rate (50.8%), White women had the lowest, (30.6%), and the prevalence of obesity among Hispanic women fell in between (40.1%).

Increasing obesity rates are also affecting children and adolescents in the U.S. and NYS. The prevalence of obesity among children and teenagers in the U.S. has tripled in the past 20 to 30 years to 16.5% among children, aged 6-19 years, and doubled to 10.3% among preschool children, aged 2-5 years (Hedley et al., 2004). Based on self-reported height and weight, the prevalence of high school students in New York City and upstate New York who are overweight or obese increased between 1999 and 2003 (Figure 5).

Figure 5: Trends in overweight and obesity among high school students in New York City and New York State, 1999-2003
Source: Youth Risk Behavior Surveillance System (YRBSS) - 1999, 2001, and 2003

Recent data indicate that 29.5% of high school students in New York City and 28.3% of high school students in upstate New York are overweight or obese. As in adults, minority youth are disproportionately affected by overweight and obesity. The rate of obesity was highest for Black teens (12.2%), followed by Hispanic teens (10.0%) and White teens (7.4%). Close to 20% of Hispanic teens and Black teens are overweight compared to 13% of White youth (YRBSS).

The prevalence of obesity among elementary school children in NYS has also increased dramatically between 1988 and 2003-2004. Based on measured height and weight in 2003, 24% of elementary school children (grades K-5) in New York City were obese (Figure 6).

Figure 6: Proportion of elementary school children in upstate NY and New York City who are obese

Source: Upstate NY, Grade 3 Oral Health, Physical Activity, and Nutrition Survey, 2004. New York City; Am J Public Health, 2004; 94: 1498. U.S.: NHANES, 1999-2002, J Am Med Assn 2004;291:2847-2850.

In 2004, 21% of third grade school children in upstate New York were obese. These prevalence rates greatly exceed the prevalence reported for the U.S. (15.8%) in NHANES 1999-2002, and the Healthy People 2010 target of 5%. In both New York City and upstate NY, prevalence rates differed across racial/ethnic categories; Hispanics have the highest rates (29.3% and 31.1%), with rates for non-Hispanic Whites the lowest (18.7% and 15.9%), and rates for non-Hispanic Blacks in between (22.5% and 22.8%, respectively).

For preschool-age children in NYS, data are only available for children from low-income families enrolled in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). The prevalence of obesity among children aged 2 to 5 years was 50% higher among low-income children in NYS WIC (Pediatric Nutrition Surveillance System (PedNSS), 2003) than among the U.S. sample (NHANES, 1999-2002), 16.1% vs. 10.3%. In 2003, 16.1% of children aged 2 up to 5 years were obese, and another 16.1% were overweight. Obesity prevalence rates among the NYS children were highest for Hispanics (21.7%), lowest for Whites (12.8%), and in between for Blacks (15.4%) (Figure 7). These rates all exceed the Healthy People 2010 target of 5%.

Figure 7: Proportion of children who are overweight (aged 2 to 5 years).

Source: NYS, Pediatric Nutrition Surveillance System (PedNSS), 2003 NHANES, 1999-2002, J Am Med Assn 2004; 291: 2847-2850.

Low Public Recognition of Obesity as a Public Health Problem

Media coverage related to obesity-related issues has increased fivefold between 1999 and 2004 resulting in an increased public awareness of obesity (IOM, 2004). While one study in California finds that one in three residents believes that unhealthy eating habits or lack of physical activity threatens children’s health (Field Research, 2003; IOM, 2004), most studies find that obesity is not perceived as a serious health problem by most Americans (IOM, 2004).

Most parents often don’t perceive obesity as a health problem for young children, especially if there are no concomitant medical problems (Baughcum et al., 2000; Jain et al., 2001), while school-age children do not view obesity as a health problem until it significantly affects their appearance or performance (Borra et al., 2003).

In a recent poll of U.S. adults, half viewed obesity as a public health problem that society needs to solve, while half considered it a personal responsibility or choice (Lake Snell Perry and Associates, 2003; IOM, 2004). Until the perception of risk associated with obesity is recognized and awareness of the public and individual health risks is appreciated, public health efforts will be stymied. Consistent with previous public health efforts that have focused on protecting children first, there appears to be more support for societal, policy and regulatory changes affecting children than for adults because children are often perceived as more vulnerable. Public health approaches and parallels to motor vehicle safety and tobacco exposure can help guide public health and policy interventions to prevent overweight and obesity.