The epidemiology of obesity☆
Introduction
The worldwide prevalence of overweight and obesity has doubled since 1980 to an extent that nearly a third of the world population is now classified as overweight or obese [1]. Obesity adversely affects nearly all physiological functions of the body and comprises a significant public health threat. It increases the risk for developing multiple disease conditions, such as diabetes mellitus [2], cardiovascular disease [2,3], several types of cancers [4], an array of musculoskeletal disorders [5], and poor mental health [6], all of which have negative effects on the quality of life, work productivity, and healthcare costs. In the US, it has been estimated that the health costs incurred by a single obese individual was US$1901 per annum in 2014, extrapolating to US$149.4 billion at the national level [7]. In Europe, the total direct and indirect cost attributable to overweight and obesity was equivalent to 0.47–0.61% of the GDP [8].
The World Health Organization (WHO) defines overweight and obesity as abnormal or excessive fat accumulation that presents a risk to health [9]. The body mass index (BMI), calculated by dividing the body weight in kilograms by the square of height in meters, is a simple metric used to indicate overall body fatness [9]. For adults, current guidelines from the US Centers for Disease Control and Prevention (CDC) and the WHO define a normal BMI range as 18.5 to 24.9, whereas a BMI ≥ 25 kg/m2 is considered to be overweight, and a BMI ≥ 30 kg/m2 is classified as obese, with severe obesity defined as a BMI ≥ 40 kg/m2 [9]. Despite this relatively simplistic definition, obesity is a multifactorial disease that results from chronic positive energy balance, i.e. when dietary energy intake exceeds energy expenditure. Excess energy is converted to triglyceride which is stored in adipose tissue depots that expand in size, thereby increasing body fat and causing weight gain. The globalization of food systems that produce more processed and affordable food, and promote passive overconsumption from energy-dense, nutrient-poor foods and beverages has been identified as a major driver of the obesity epidemic [10], although a decrease in physical activity owing to the modernization of lifestyles is also likely involved [11,12].
Obesity can occur at any age. Previous studies assessing trends in obesity found that its prevalence has increased in both adults and children of all ages, indiscriminate of geographical locality, ethnicity or socioeconomic status [1]. In low-income countries, obesity is generally more prevalent among middle-aged adults from wealthy and urban environments (especially women); whereas, in high-income countries, it affects both sexes and all ages, but its prevalence is disproportionately greater among disadvantaged groups [10].
In this article, we summarize the prevalence rates and secular trends of overweight and obesity in adults on a global scale.
Section snippets
Methods
We used the data provided by the Global Burden of Disease Study (Institute for Health Metrics and Evaluation, Seattle, WA) [1], which defines obesity as a BMI ≥ 30 kg/m2, and overweight as a BMI ≥ 25 kg/m2 (i.e. overweight rates include obesity); the full data file is available online from Global Health Data Exchange (http://ghdx.heathdata.org).
We divided the world into six regions according to WHO; namely African, Americas, Eastern Mediterranean, European, South East Asian and Western Pacific.
Prevalence of Overweight and Obesity by Sex and Age
Globally, a total of 1.9 billion and 609 million adults were estimated to be overweight and obese in 2015, respectively, representing approximately 39% of the world's population. Fig. 1 shows the global prevalence rates of overweight and obesity in 2015, for adult men and women aged > 20 years, by age group. In 2015, the prevalence of overweight was somewhat lower in women than in men among young adults (aged between 20 and 44 years) but this trend was reversed after age 45–49 years, perhaps
Discussion
The worldwide prevalence rates of overweight and obesity have approximately doubled since 1980 to an extent that over one-third of the world's population is now classified as overweight or obese. Kelly et al. estimated that 57.8% of the world population will be overweight or obese by the year 2030 if the current trends continue [13]. Globally, the proportion of individuals with a BMI ≥ 25 kg/m2 increased between 1980 and 2015 from 25.4% to 38.5% in men, and from 27.8% to 39.4% in women. The
Author Contributions
Y.C.C. and C.D. collected and analysed the data. Y.C.C. drafted the manuscript. All authors were involved in manuscript editing and approved the version submitted for publication.
Duality of Interest
The authors have no conflicts of interest relevant to the content of this article.
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Disclosure: The author reports no conflicts of interest in this work.