Obesity Epidemiology

INTRODUCTION TO OBESITY EPIDEMIOLOGY 9A life-course approach to obesity prevention requires the identification of interveningrisk factors across different life stages, including intrauterine exposures, infant feedingpractice, parental influences, school environment, and adult-life transitions. Several birthcohort studies have been established to examine age-specific risk factors for obesityand associated chronic diseases. Results from these studies are particularly valuable inidentifying risk factors for infant and childhood obesity, which can then be used to guidepreventive efforts during critical periods of development.A Multilevel Pathway Model of ObesityKim and Popkin 64 proposed a multilevel pathway model to depict multifactorial causationof obesity as well as multiple health consequences engendered by obesity. In this model,overweight and obesity are considered intermediate outcomes in the causal pathway thatlinks dietary factors, physical activity, fetal/infant development, genetics, and socioculturalvariables to development of chronic diseases, including diabetes, cardiovascular diseases,and cancers. Effects of overweight and obesity on chronic diseases are mediated throughmetabolic disorders, including hypertension, dyslipidemia, and insulin resistance.This model highlights the dynamic nature and complexity of obesity epidemiology.It has important implications for analysis and interpretation of data on the causes ofobesity and the relationship to mortality. For example, in many studies of obesity andmortality, controlling for blood cholesterol, hypertension, and diabetes attenuates or eveneliminates the effects of BMI on cardiovascular disease and total mortality. 65 However,the results of such analyses should be interpreted carefully, because high cholesterol,hypertension, and diabetes are biological intermediates—factors that mediate, in part,the effects of obesity on chronic disease and mortality.Domains of Obesity Epidemiology ResearchThe goal of obesity epidemiology is to identify the determinants and consequences ofobesity, thereby informing prevention and intervention strategies. By definition, obesityepidemiology encompasses a variety of research activities. These include monitoringpopulation trends, identifying genetic and environmental risk factors, examining healthand other consequences of obesity, and carrying out intervention studies on preventionor treatment. As shown in a conceptual model similar to that used in physical activityresearch, 66 the different domains of obesity research are interrelated; findings fromeach inform the others (Fig. 1.2). For example, population trends detected in descriptiveepidemiology may prompt analytic epidemiologic studies of risk factors. These reportsmay, in turn, guide obesity prevention and intervention research.Results from epidemiologic studies of obesity in relation to disease outcomes andmortality are crucial to the development of healthy weight guidelines and recommendations.Basic or mechanistic research on obesity, although not part of obesity epidemiol ogy,plays an important role in understanding biological mechanisms, causes, and consequencesof obesity. This knowledge can help with the interpretation of findings from epidemiologicand intervention studies and guide further in-depth investigations of novel risk factorsand treatment modalities. Sound study design, analysis, and interpretation, as well asvalid measurements of body fatness and energy balance, are crucial to all epidemiologicresearch. In subsequent chapters, we will discuss each of these topics in detail. We brieflysummarize key research domains in obesity epidemiology in the following pages.