Obesity: Global Impact and Epidemiology

Obesity continues to accelerate resulting in an unprecedented epidemic that shows no significant signs of slowing down any time soon. The World Health Organization reports that in 2016, nearly 2 billion adults were overweight and that worldwide obesity has nearly tripled since 1975. Obesity: Global Impact and Epidemiology is an important tool in proving a link to new knowledge, serving researchers and clinicians. The field of obesity is evolving very quickly and there is an abundance of scientific data that has emerged and is emerging constantly. Researchers and physicians need new updated information about the epidemiology and global impact of obesity that come from authors that have a wide perspective in the field. For health professionals and researchers, there is a need to understand how obesity begins. While a simple question, the answer is very complex.

• Serves as a starting point for in-depth discussions in academic settings, leading to revised and updated treatment options for practicing obesity-treatment specialists
• Offers practical information about the methodology of epidemiologic studies of obesity
• Updated important source of information for clinicians and scientists in the field of obesity

• Language: English
• Publisher: Elsevier Science
• Release date: Jul 15, 2020
• ISBN: 9780128188408

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Preface

Raman Mehrzad, M.D., M.H.L., M.B.A.

The World Health Organization has declared obesity a global epidemic. Its prevalence has more than doubled since 1980, causing a myriad of health problems for children and adults. Today, more than one-third of the world’s population is classified as obese or overweight. If this trend continues, researchers estimate that by the year 2030, this number will reach more than 50%. Although recognized clinically as an important condition that increases the risk of multiple diseases and is a major contributor to morbidity and mortality, it is only in recent years that obesity has been identified as a population-wide problem that requires preventive action. Due to its complex and multifactorial nature, however, prevention and slowing the incidences have been challenging.

In order to know where we can go, we need to know where we are in this major epidemic. Therefore, epidemiological studies in obesity are of utmost importance because they identify risk factors that may represent critical control points for this global problem. Moreover, obesity is an evolving field with continuous research being pursued by numerous medical specialties and scientists around the world. Each year, multiple new studies and evidence-based guidelines are being published on this topic. Therefore, this book offers the latest science in the field of obesity epidemiology that analyzes the distribution (who, when, and where), patterns, and determinants of obesity. This book will depict everything from analytic epidemiology designs in obesity research to prevalence and trends in obesity in the United States and affluent countries to environmental and cultural factors related to the obesity epidemic to obesity’s consequences and conditions in defined populations around the globe.

The target audience for this book includes the majority of folks in the medical field, as obesity is an area related to almost every field in medicine. More specifically, healthcare professionals in the fields of general surgery, plastic surgery, internal medicine, endocrinology, obesity medicine, cardiology, and gastroenterology as well as Ph.D. students and scientists focusing on metabolism obesity research will benefit from this book immensely. Medical students, nursing students, nurse practitioners, physician assistants, medical residents, and fellows are also students that would find value in this book.

Chapter 1: Definition and introduction to epidemiology of obesity

Raman Mehrzad, M.D., M.H.L., M.B.A.    Department of Plastic and Reconstructive Surgery, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States

Abstract

Obesity is a global, complex, multifactorial, and generally preventable disease. The global prevalence of obesity has doubled in the past 40 years regardless of sex, age, ethnicity, or socioeconomic status. Today, more than one-third of the world’s population is classified as obese or overweight. If this trend continues, researchers estimate that by 2030, this number will surpass 50%.

Keywords

Epidemiology studies; Health care costs; Prevalence; Multidisciplinary approach; Objective; Physiological functions

Overview and definition of obesity

Obesity is a global, complex, multifactorial, and generally preventable disease [1]. The global prevalence of obesity has doubled in the past 40 years regardless of sex, age, ethnicity, or socioeconomic status. Today, more than one-third of the world’s population is classified as obese or overweight [2]. If this trend continues, researchers estimate that by 2030, this number will surpass 50% [3].

Obesity is typically defined as excess body weight for height. Today, due to its simplicity and low cost, body mass index (BMI), defined as the weight in kilograms divided by the height in meters squared (kg/m²), is the most common measure of obesity. The National Institutes of health (NIH) and the World Health Organization (WHO) define overweight as having a BMI between 25.0 and 29.9 kg/m², and obesity as having a BMI > 30.0 kg/m² [4, 5].

For children, the criteria for overweight are based on the 2000 US Centers for Disease Control and Prevention (CDC) BMI-for-age growth charts in the United States. Here, at or above the age-specific 95% BMI percentile is defined as overweight. Those at risk for overweight are defined as having a BMI between the 85th to 95th percentiles of the BMI-for-age growth chart [6].

Recently, there has been more evidence suggesting that abdominal fat rather than total body fat is an independent risk factor of cancer-related and cardiovascular outcomes. It has been suggested that the visceral and metabolically active fat surrounding the organs causes metabolic dysregulation, which in turn predisposes to disease. This is also known as the metabolic syndrome, which per international guidelines is a collection of dysmetabolic conditions that puts individuals at increased risk for cardiovascular disorders [7]. Nowadays, it is therefore common practice to measure the waist and hip circumference as well as the waist-to-hip ratio. It should be noted that the waist circumference that is defined to increase the risk for disease is different depending on race. For instance, waist circumferences > 94 cm in European men and > 80 cm in European women are linked to higher cardiovascular risk, although in the Asian population, the cut-off is 90 vs. 80 cm for men and women, respectively [8].

Brief prevalence of obesity

Recent epidemiology studies have estimated that a total of 1.9 billion people worldwide were obese or overweight in 2015. This represents 39% of the world’s population [3]. The prevalence is somewhat lower in women than men among ages 20–44; however, from 45 to 49, the trend reverses between the genders. Generally, obesity rates start to increase at 20 and peak between 50 and 65 with a slight decline subsequently. An increase of nearly 50% has been seen in the age-standardized prevalence in obesity over the past 3.5 decades, from 26.5% in 1980 to 39% in 2015, while the prevalence increased by 7% to 12.5% during the same time frame, accounting for an almost 80% increase [3]. Women had a greater rate of overweight and obesity than men in this period. The prevalence of obesity is largely uniform globally, although there are some variabilities between regions and countries [3].

Epidemiological studies

The purpose of epidemiological studies is to capture a baseline of where we stand on the issue of obesity as well as to identify the determinants and consequences to later find strategies for prevention and intervention. The epidemiology of obesity covers different research activities with the aim to study and monitor risk factors, consequences, and population trends, and to conduct studies on how to prevent and treat obesity [9].

Epidemiology studies in general are crucial to identify trends and patterns and later develop guidelines and recommendation for the population. Many of the current strategies have emerged from data of epidemiological studies [9]. For instance, the knowledge of the consequences of obesity has made us aware that this is a danger to health. Therefore, we now measure BMI and waist circumference, track the progress of weight gain and loss, etc. It has also resulted in emphasizing treatment options for patients that are at risk of obesity or are in the class of different stages of obesity. Therefore, continuous reports of these data are important to be able to refine our recommendations for patients and decrease mortality and morbidity. Moreover, studies on epidemiology encourage other research areas to actively analyze various molecular mechanisms, which further can identify targets for pharmaceutical approaches. A couple of examples of this are medications such as Orlistat (Xenical) and Lorcaserin (Belviq). These drugs target enzymes, receptors, and hormones that have been found to play a role in fat absorption and appetite [10, 11].

Multidisciplinary approach to obesity

Obesity is a multidisciplinary approach. Internists, cardiologists, endocrinologists, surgeons, dieticians, psychologists, and behavioral therapists are just a few that take care of patients with obesity. Although each provider may focus on specific areas, they are all needed in preventing and treating obesity. Likely, the cause of this is the complexity of the disease. Losing weight in a society where there are numerous temptations has been found to be difficult. Thus, providers from different specialties are needed to assist patients and optimize their results. In fact, studies show that a multidisciplinary approach is more effective for weight loss and maintenance [12–14].

Similarly, accurate study designs, valid measurements, experienced researchers, and collaboration between scientists and clinicians are important to make this research area optimal. Fig. 1 is a conceptualized flowchart that describes the different areas and interrelationships within epidemiological research.

Fig. 1 Conceptual framework for the interrelationships among obesity epidemiology research domains. Adapted from Welk GJ. Introduction to physical activity research. In: Welk GJ, editor. Physical activity assessments for health-related research. Champaign, IL: Human Kinetics; 2000. p. 3–18.

Health consequences of obesity

Obesity has many serious health consequences. It adversely affects nearly all physiological functions in the body and increases the risks of cardiovascular diseases, hypertension, hyperlipidemia, chronic kidney disease, diabetes, cancers, musculoskeletal disorders, and poor mental health, just to name a few [15–19]. This area of research has grown significantly over the past few years, partly because obesity is an epidemic and partly because we now also have better quantitative methods in the field with the availability of body size or adiposity measurements in all epidemiological or clinical studies. Although these studies continue to improve our understanding of the disease and its healthcare consequences, there are still many questions that remain between the relationship of adiposity and how it brings different disease states as well as the impact of obesity on mortality [9]. To conduct studies that answer the above, careful considerations of epidemiological study design, analysis, and interpretation need to be made by scientists and clinicians.

Brief etiology of obesity

The etiology of obesity is molecularly simple to understand. A higher calorie intake than calorie expenditure results in a net positive calorie excess that in turn causes weight gain. Although this is simple mathematics, the actual regulation of body weight and fat is very complex and is a complicated interrelation of behavioral, genetic, endocrine, psychosocial, and environmental factors. Although we understand many of the causes of obesity, understanding these interrelations and other contributing factors remains to be elucidated. One of the issues with studies that determine the predictors of obesity is that they have many methodological problems such as reverse causation, confounding, and imprecise diet and physical exercise. In general, calorie intake and expenditure are many times subjective and not always easy to measure properly by patients or clinicians. Furthermore, obesity could at times bring certain behaviors and vice versa, and therefore reverse causation bias is a commonly encountered issue. These problems result in limitations when attempting to design study methods and make accurate conclusions.

Cost of obesity

The US health care costs of obesity are enormous. The cost of obesity is in the hundreds of billions in the United States per year as well as a significant portion of the gross domestic product in Europe when accounting for both direct and indirect costs. A more detailed report of the economic impact can be found in Chapter 5 [20, 21].

Goal of obesity research

The major objective to obesity research is to prevent it from happening and to treat those who are affected by it. Many studies on different dietary strategies and lifestyle modifications have been done at different levels: individual, community, school, and society. While we have many different tactics for the prevention and treatment of obesity, sufficient and sustainable interventions are yet to be found. This is true because regardless of the numerous strategies, the obesity trend is still growing, which proves that the problem is very complex [9].

References

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[2] IHME. Global burden of disease study 2015 (GBD 2015) obesity and overweight prevalence 1980–2015. Seattle, WA: Institute for Health Metrics and Evaluation (IHME); 2017.

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[6] US Centers for Disease control and Prevention. Overweight and obesity. Available at: http://www.cdc.gov/nccdphp/dnpa/obesity/trend/maps/index.htm. 2008 [Accessed 22 October 2009].

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[8] Alberti K.G., Zimmet P., Shaw J., IDF Epidemiology Task Force Consensus Group. The metabolic syndrome—a new worldwide definition. Lancet. 2005 Sep;366(9491):1059–1062.

[9] Hu F.B. Introduction to obesity epidemiology. In: Obesity epidemiology. Oxford University Press; 2008 Chapter 1.

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[13] Ma C., Avenell A., Bolland M., Hudson J., Stewart F., Robertson C., Sharma P., Fraser C., MacLennan G. Effects of weight loss interventions for adults who are obese on mortality, cardiovascular disease, and cancer: systematic review and meta-analysis. BMJ. 2017 Nov 14;359:j4849.