Trends in the Association of Poverty With Overweight Among Adolescents, 1971–2004.

We examined whether socioeconomic disparities in adolescent overweight status increased, decreased, or remained constant during the past 3 decades and whether these trends varied by age among US adolescents. Our results indicated an increasing disparity in adolescent overweight status by family poverty among adolescents aged 15 to 17 years but not among adolescents aged 12 to 14 years. For the older adolescents, the magnitude of the increase in the disparity was similar across the demographic subgroups of male, female, non-Hispanic white, and non-Hispanic black respondents. For the younger adolescents, no disparity in overweight by family poverty was apparent for any demographic group at any of the 4 survey years; although among non-Hispanic black adolescents, the overall rate of overweight during the course of the surveys increased faster in nonpoor vs poor families, a finding consistent with trends in the adult population.

To our knowledge, our study is the first to document an increasing disparity in overweight by poverty status in any US population group. These results challenge the current conclusion that disparities in overweight by poverty status have not increased in the United States, a conclusion based on analyses of adults and also from data from the mid-1990s that combined younger and older adolescents into a single group. Our findings that later adolescence is a life stage with a unique association between poverty and overweight is plausible because both food choices and physical activity levels in adolescence differ considerably from those earlier in childhood and adulthood. Our results therefore point to the utility of a life-course perspective that takes into account findings specific to life stages.

What factors explain an overweight disparity by poverty status that is specific both to older adolescents and also more recent NHANES surveys? The observed differences across older vs younger adolescents are consistent with the greater autonomy that comes with increasing age. Adolescents aged 15 to 17 years vs those aged 12 to 14 years have more opportunities to purchase their own food and determine their own leisure time pursuits and also have more discretionary income with which to act on their preferences.

After identifying trends in poverty and adolescent overweight among older adolescents, we then examined ex post facto trends in specific behaviors that may play a role in this disparity. Our analysis investigated dietary behaviors with documented increases in recent years, including sweetened beverage consumption, eating out, and snacking between meals. We also examined physical inactivity and breakfast skipping, which observational studies show to be associated with adolescent overweight. A behavior involved in the emerging disparity identified in our study should fulfill a specific and detailed set of 4 expectations. This disparity should have higher prevalence for those families in poverty, higher prevalence among adolescents who are overweight, show a greater disparity by poverty status among older vs younger adolescents, and have developed in recent years.

Proportion of calories from sweetened beverages followed this exact pattern of findings, suggesting that recent trends in sweetened beverage consumption among older adolescents may, at least in part, explain the disparity in overweight status. Physical inactivity also followed this pattern of findings, although measures were restricted to the most recent NHANES survey and historical comparisons were not possible. Other studies have noted that physical inactivity among adolescents has been increasing in recent years. These results suggest that policy and prevention efforts that target these behaviors for overweight can be further justified and motivated by the potential of these efforts to reduce an emerging socioeconomic disparity in adolescent overweight.

Breakfast skipping also came close to fulfilling all 4 criteria, with the exception that in the most recent NHANES survey the recently emerged disparity had the same magnitude for younger and older adolescents. These results point to breakfast skipping as a factor that warrants more attention in the study of adolescent overweight. To our knowledge, there has been no randomized controlled trial of breakfast promotion for overweight prevention or treatment, and many of the intervening mechanisms remain speculative. One longitudinal study showed that adolescents with normal weight who skipped breakfast were more likely to experience BMI increases over time. This result supports possible mechanisms, such as rebound overeating at lunch and dinner, a poor dietary pattern characterized by soda and snacking in place of regular meals, or possibly a biological effect associated with efficient calorie utilization after long periods of not eating. At the same time, breakfast skipping may also be used as a dieting strategy among overweight individuals.

Our study was limited to analysis of risk factors that were measured in the NHANES surveys, and these are likely only a subset of a much larger pool that are at work in the emerging disparity in adolescent overweight by poverty. Availability of energy-dense food perceived dangerousness of neighborhoods and limited access to supermarkets that sell nutritious, low-calorie food are a few examples of additional circumstances that are currently linked to adolescent overweight and warrant more attention in analysis of disparities in overweight. At the same time, current influences that have fostered a socioeconomic disparity in adolescent overweight have emerged recently and new factors may emerge in the near future. Ultimately, successful intervention and prevention of the emerging disparity will require constant surveillance of potential intervening mechanisms and, ideally, attention to the upstream influences that set these intervening mechanisms into motion.

Our study has some limitations. The BMI-based definition for adolescent overweight is recommended by the CDC, but the best way to identify overweight and obesity in children is still a subject of debate. Another limitation is that data from Hispanic adolescents could not be meaningfully analyzed due to differences in sampling strategies and in measurement of Hispanic ethnicity across the NHANES surveys. Furthermore, the sample sizes were too small to allow examination of sex differences within racial/ethnic groups over time, which are present among adults. The cross-sectional design and methods used for NHANES limit investigation to only broad, major risk factors for overweight and do not have the precision to measure small, cumulative energy imbalances of only dozens of calories that can lead to overweight if experienced over protracted periods.

Finally, our measurement of family socioeconomic status is limited to self-reported family income, because the NHANES data lack consistent measures of other socioeconomic status components, such as family education, wealth, neighborhood conditions, and past socioeconomic status experience. Socioeconomic status is a multidimensional construct and single measures of socioeconomic status should be accompanied by measures of other socioeconomic status dimensions when data are available.

Counterbalancing these limitations are the strengths of our study. The main study finding of an increasing socioeconomic disparity in overweight among adolescents aged 15 to 17 years was robust across 4 different weight status indices and across sex and racial subgroups. Additional strengths include the NHANES measurement of height and weight by trained technicians, which removes the results from the potential biases associated with self-reports, and that the sample is representative of all US adolescents.

In conclusion, a widening disparity in overweight that disadvantages adolescents in poor families has emerged in the 15- to 17-year-old age group in recent years. These results suggest that efforts to reduce health disparities in the United States require monitoring of population health, so that emergent disparities and their underlying causes can be detected and addressed at early stages of their development.