contribute to obesity, but the rapid increase in obesity rates within the past decade follows a change in human behavior, not a change in genetic makeup (Hill 2006). Today, our unchanged biology, one that has undergone millennia of evolution, survives in an environment in which the pace of change rapidly outstrips the rate of adaptation. It is an environment that in multiple ways supports less activity and invites caloric excess. There is no one way to address the obesity problem, but there are multiple opportunities to reshape our physical environment and adjust our responses to the situation at hand.
In addition to the continuing work of medical science, curbing the obesity explosion poses behavior-related challenges at three distinct levels, each of which has a different role and responsibility in addressing this issue.
1. To the individual, who assumes responsibility for his or her self-care decisions.
2. To the health care system, which informs and supports individual efforts to make sustainable dietary and activity lifestyle changes.
3. To society, which promotes an environment that increases access to nutrient-dense food and physical environments that invite activity.
This book is about the second challenge. How do health care professionals interact with patients in a way that supports each individual’s innate interest in their own well-being?
Chapter 2
The Burden on Society
Increasing Prevalence
Obesity rates are climbing, not just in the U.S. but also in more and more countries around the world. Figure 1 shows the prevalence of obesity around the world (WHO 2000, WHO 2010a). The current number of obese Americans is the highest ever recorded. The escalating health risks due to obesity increase the prevalence of chronic disease and health care costs around the world.
Figure 1—Global weight increases, 1991 and most recent available
Obesity is defined as abnormal and excessive fat accumulation that may impair health (WHO 2009). To assess the health risks of obesity, clinicians use body mass index (BMI), a measure of weight compared with height. BMI is an imperfect tool, but provides a more useful measure of total body fat than weight alone. BMI risk levels are based on the association between BMI and morbidity/mortality for adults over 20 years of age and are the same for both sexes. According to BMI categories, all people with a BMI of 25 kg/m2 or greater are considered overweight. Overweight subcategories are pre-obese for a BMI of 25–29.9 kg/m2 and clinically obese for a BMI ≥30 kg/m2 (CDC 2010). As a general estimate of body fat, BMI is helpful for comparing populations, but consideration of factors such as age (older adults lose muscle and gain fat), fitness level (athletes have more muscle), and genetic variation (cutoff points are lower in Asian populations) may modify risk points for individuals.
Based on these criteria, The National Health and Nutrition Examination Survey (NHANES) 2007–2008 (Ogden 2010) reveals that in the U.S.
• 68% of adults older than 20 years are overweight, and 34% of that population is obese
• More men (72%) than women (64%) are overweight, but more women (36%) than men (32%) are obese
• Obesity rates are higher in minority populations, especially among women: 50% of non-Hispanic blacks, 43% of all Hispanics, and 33% of non-Hispanic white females are obese
• Overall, 6% of people are extremely obese, with a BMI ≥40 kg/m2
Data from the NHANES surveys (1976–1980 and 2003–2006) show that the prevalence of obesity has increased for children from 5.0% to over 17% during that period (CDC 2010).
BMI in childhood correlates significantly with BMI in adulthood (Ferraro 2003, Zhao 2011). Young people who are already obese at age 10–15 years are fast becoming the adults who continue to gain weight at the rate of 1.8–2.0 pounds per year between 20 and 40 years of age (Pi-Sunyer 2005). The problems associated with obesity are poised to worsen. Figure 1 helps show how obesity is becoming a worsening global problem.
Escalating Burden
As obesity rates rise, the negative consequences of the condition increase. The costs of obesity to society include impaired physical health, impaired mental well-being, and diverted financial resources.
Impaired Physical Health
Obese persons generally experience more health and mobility problems than do nonobese persons (CDC 2001, Adolfsson 2004). Although not everyone who is obese experiences more health problems than their leaner counterparts (NHLBI 2000), obesity does increase the risk for impaired well-being and for several major diseases.
The link between excess body fat and type 2 diabetes is especially clear. Despite different measures of fatness and different criteria for diagnosing type 2 diabetes, there is a consistent association between excess weight and type 2 diabetes across differing population groups, supporting the strength of this connection (WHO 2000). Colditz (1990) and Chan (1994) report that as many as 65–75% of the people diagnosed with type 2 diabetes would not have developed the disease if their BMI had remained ≤25 kg/m2. As a result, the explosive increase in obesity predicts an associated increase in type 2 diabetes. Some have referred to this link between obesity and diabetes as “diabesity” (Zimmet 2001, Astrup 2000).
Sources agree that the number of children (aged <20 years) diagnosed with type 2 diabetes has increased significantly in the past decade, but no data exist to document the number. Minority adolescents, especially if overweight, are those most likely to have type 2 diabetes. A CDC/NIDDK study, Search for Diabetes in Youth, is collecting data to learn more about the character, treatment, and impact of a diabetes diagnosis on children and youth (Mayer-Davis 2009).
Overweight and obesity now rank as the fifth leading global risk for mortality. In addition, 44% of the diabetes burden, 23% of the ischemic heart disease burden, and 7–41% of certain cancer burdens are attributable to overweight and obesity (WHO 2009). Table 1 outlines additional risks associated with obesity (WHO 2000).
Table 1—Relative Risk of Health Problems Associated with Obesity
Both an individual’s fat distribution (i.e., waist circumference) and amount of fat (i.e., BMI) predict health risks (IDF 2006). Abdominal obesity may predict type 2 diabetes more accurately than overall fatness (Pi-Sunyer 2004). (See chapter 7 for more information.)
In addition to the amount and distribution of fat, there is a cluster of disease risk factors that are particularly important to consider when treating overweight or obese individuals (Kahn 2005).
This constellation of interrelated risk factors is often called the metabolic syndrome, and it is strongly associated with obesity, cardiovascular disease, and diabetes. Indicators of metabolic syndrome include dyslipidemia, elevated glucose, hypertension, abdominal obesity, and insulin resistance. In combination, these conditions synergistically increase risk. To help identify and treat the underlying problems, sets of diagnostic criteria have been developed. The American Heart Association and the National Heart, Lung, and Blood Institute updated the widely-used National Cholesterol Education Program (NCEP) Adult Treatment Panel III (ATP III) with minor modifications in 2005. The changes in criteria lower the threshold for diagnosis by
1. lowering the cutoff point for elevated blood glucose, and
2. considering a categorical cut point met with drug therapy as a risk factor (Grundy 2005).
The presence of three or more of the risk factors in Table 2 constitutes a diagnosis of metabolic syndrome.
Table 2—Diagnostic Criteria for Metabolic Syndrome
In 2006, the IDF published a worldwide definition of the metabolic syndrome