Pathogenesis, Prevalence and Epidemiology of Obesity

Obesity has been a recognised factor in poor health outcomes from as early as the nineteenth century (Berghöfer et al., BMC Public Health 8:200, 2008). However, despite this knowledge, its prevalence has gradually increased over the past 100 years (Yang et al., Epidemiol Rev 29(1):49–61, 2007). Most recent estimates state that 15% of the global population is overweight (Yang et al. Epidemiol Rev 29(1):49–61, 2007), with that figure set to grow continuously in the coming years. Weight gain has been shown to play a role in the development of cardiovascular and respiratory illnesses, osteoarthritis, numerous rheumatological diseases and several different types of cancer (Berghöfer et al., BMC Public Health 8:200, 2008; Marques et al., Eur J Public Health 28(2):295–300, 2018; Ogden et al., NCHS Data Brief 219:1–8, 2015; Hales et al., NCHS Data Brief 288:1–8, 2017). Initially, the thinking behind weight gain and the increasing incidence of obesity was thought to be simple cause and effect. An individual would be able to control their weight if their calorie input was equal to or less than their daily calorie requirements (Pontzer, Exerc Sport Sci Rev 43(3):110–116, 2015). However, this input/output or linear relationship has been shown to be overly simplistic. More recent research has shown that weight gain is a multifactorial issue. Genetics, diet, geographical factors and socio-economic status have all been shown to have an influence on dictating how easy or difficult it is for an individual to maintain a healthy weight (Chooi et al., Metabolism 92:6–10, 2019; Kersten, EMBO Rep 2(4):282–286, 2001; La Vecchia and Majem, Lancet Glob Health 3(3):e114–e115, 2015; Popkin and Hawkes, Lancet Diabetes Endocrinol 4(2):174–186, 2016; Imamura et al., Lancet Glob Health 3(3):e132–e142, 2015; Pontzer, Exercise Sport Sci Rev 43(3):110–116, 2015). This chapter will discuss these concepts in greater detail.