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In 2016, a total of 671 million adults (15.7% of women and 11.6% of men) and 124 million children (5.6% of girls and 7.8% of boys) had obesity [1]. If current trends continue unabated, by 2025, the global prevalence of obesity is predicted to exceed 21% in women and 18% in men [2]. At the country level, US‐based simulations previously suggested that the prevalence in adults would plateau at 32% by 2030 [3]. However, the most recent US data (2017–2018) suggest this percentage has already been surpassed with the national prevalence among adults currently 42% [4]. Simulations in Mexico suggest an even higher obesity plateau at 57% of women and 54% of men by 2050 [5], and simulations in Russia suggest that men will far surpass women with a prevalence of obesity of 76% in men compared to 54% in women by 2050 [6]. The call for evidence‐based action against the rising tide of obesity has never been more urgent.

The global obesity epidemic has been officially recognized by the World Health Organization (WHO) since as early as 1997 [7]. Since then, over the past two decades, governments have repeatedly set targets to address obesity. In the United States, an obesity prevalence target of 30.5% was set as part of the Healthy People 2020 strategy, and was loosened to 36.0% as part of the Healthy People 2030 strategy [8]. On a global scale, in 2013, the United Nations World Health Assembly adopted a global target of halting the rise in obesity by 2025 as part of the targets aimed at reducing premature death from noncommunicable diseases (NCDs). The WHO’s “Comprehensive Implementation Plan for Maternal, Infant and Young Child Nutrition” sets the same target for children [9]. To date, no country is on track to meet targets in adults or children [10]. In every country in the world, over the past four decades, obesity has steadily risen [11]. Only in a handful of population subgroups such as young children is the prevalence starting to plateau, albeit at high levels [11].

Trends in the global patterning of obesity have led to the development of the obesity transition conceptual framework [12]. Stage 1 is characterized by a higher prevalence of obesity in women than in men, in those with higher socioeconomic status than in those with lower socioeconomic status, and in adults than in children. Many countries in South Asia and sub‐Saharan Africa are presently in this stage. Stage 2 is characterized by a large increase in the prevalence among adults, a smaller increase among children, and a narrowing of the gap between sexes and in socioeconomic differences among women. Many Latin American countries are presently at this stage. Stage 3 is characterized by the “reversal hypothesis” in which the prevalence of obesity among those with lower socioeconomic status surpasses that of those with higher socioeconomic status, and plateaus in prevalence can be observed in women with high socioeconomic status and in children. The United States and most European countries are presently at this stage. A hypothetical Stage 4 would be characterized by declines in the prevalence of obesity, but no country is yet at this stage.

The strong association between obesity and novel coronavirus (COVID‐19) infection, hospitalization, admittance to intensive care units, and death may represent an important turning point for obesity prevention efforts [13]. The pandemic has triggered long‐awaited, unprecedented action by governments to tackle obesity. For example, the United Kingdom has adopted the most comprehensive obesity strategy to date [14], citing the COVID‐19 pandemic as an important driver. Public officials in Mexico have pinned “their pandemic problems on Mexicans’ unhealthy habits – starting with soft drink consumption” [15]. Indeed, the COVID‐19 pandemic may have quickened the approval of the first‐ever ban on the sale of sugar‐sweetened beverages and high‐calorie snack foods to children in the Mexican state of Oaxaca [15].

This chapter sets out to (1) describe how to define excess body fat; (2) summarize trends and current status of adult and childhood obesity, focusing on the United States (key data sources are summarized in Table 2.1); (3) summarize trends and current status of global obesity, focusing on low‐ and middle‐income countries; and (4) explore how social determinants shape the prevalence of obesity. Social determinants are the conditions in which people are born, grow, live, work, and age – they are the so‐called causes of the causes or upstream drivers [16]. In addressing the social determinants of obesity, it is recognized that individual choices are influenced by social, economic, political, environmental, and cultural factors. Specific dimensions covered in this chapter include gender, race and ethnicity, socioeconomic status, urbanization, and culture.