increases in regional brain activity in response to images of palatable food.27


These


results support the notion that the drive to eat is increased in people who have lost weight, and their perception of food-related stimuli is different from that of people of normal weight. These findings emphasize the biological nature of weight regulation and the challenges facing people who have lost weight.


Is Weight Maintenance Possible?


How, then, can anyone maintain a reduced state in the face of all the biological mechanisms that promote weight regain? Despite what could be considered the depressing message conveyed by the data related here, many people are successful at losing weight and at maintaining that weight loss over time. The National Weight Control Registry is a group of more than 10,000 people who have lost more than 23 kg (50 lb) and maintained that weight loss for more than 5 years.28


These indi-


viduals have been successful at pushing back against the physiologic mechanisms that drive weight regain in most people. They use cognitive strategies to counteract the biological drive for weight regain, including frequent self-weighing, high levels of physical activity, and the consumption of an energy-restricted, low-fat diet.


The Prevalence of Obesity


In the United States, two large epidemiologic studies have followed the preva- lence of obesity over time. One, the Behavioral Risk Factor Surveillance System (BRFSS), is a health survey system that collects data from a large, geographically representative sample of US residents regarding their health-related risk behaviors and chronic health conditions, including obesity. BRFSS uses self-reported height and weight data to calculate BMI. Because these data are self-reported, the actual prevalence of obesity is likely underestimated. The advantage of the BRFSS data set is that it provides detailed geographic estimates of obesity prevalence over time. The second data set comes from the National Health and Nutrition Examination Survey (NHANES), which uses directly measured heights and weights from a smaller sample of people that is statistically representative but not as geographi- cally comprehensive as the BRFSS sample. Although some experts thought that the rising prevalence of obesity had pla-


teaued, the most recent data suggest that the prevalence of obesity continues to rise across the United States. The most recent data from NHANES (2017–2018) showed that the prevalence of obesity among all children and adolescents aged 2 to 19 years in 2018 was 19.3%.29


2014. Among adults, the prevalence of obesity was 42.4% in 2018. From 1999–2000 to 2017–2018, the prevalence of obesity in adults increased from 30.5% to 42.4%. During the same interval, the prevalence of severe obesity increased from 4.7% to 9.2% (refer to Figure 1.11).30 Obesity disproportionately affects certain racial and ethnic groups. In 2017–


2018, the prevalence of obesity was 49.6% in non-Hispanic Black adults and 44.8% among Hispanic adults, as shown in Figure 1.12.30


These differences in prevalence


are due in part to a number of social and environmental factors including food inse- curity, aspects of the food environment, differential access to health care, financial and housing challenges, and neighborhood factors that result in barriers to physical activity. While women have more body fat at any given level of BMI, there was no difference in the prevalence of obesity in 2017–2018 between men and women.†


† Report identified participants as men and women. Gender was not further specified.


16 SECTION 1: Foundations of Treatment: The Human Element


This was up from 5.2% in 1974 and from 17.2% in


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