Epidemiology

Globally, it is often difficult to make a direct comparison of the prevalence of obesity between countries due to inconsistent classifications used for obesity. For example, the professional societies in Japan and South Korea define the BMI cutoff for obesity as 25 kg/m². This is due to the increased risk of diabetes and cardiovascular disease at lower BMIs in these populations compared with Western populations.[11][12]​ However, World Health Organization data from 2016 suggest that the worldwide prevalence of obesity (BMI ≥30 kg/m²) in adults was approximately 13%, and ranges widely from <10% in many African and Southeast Asian countries, to between 20% and 40% in Europe and the Americas, and >40% in some Pacific islands. WHO: GHO Data Repository: obesity Opens in new window[13]

In 2017, 26% of adults (both sexes) in England were classified as obese.[14] The proportions vary with age, such that the highest proportion of adults who were obese are men aged 45-64 years (36%), and women aged 45-54 years (37%).[14]

The National Health and Nutrition Examination Survey (NHANES) estimates prevalence of overweight and obesity in the US as follows:[15]

Overweight: BMI 25-30 kg/m²

  • 2005-2006: 32.6%

  • 2017-2018: 31.1%

Obesity: BMI ≥30 kg/m² (class I: BMI of 30 to <35 kg/m²; class II: BMI of 35 to <40 kg/m²)

  • 2005-2006: 34.3%

  • 2017-2018: 42.5%

Severe obesity: BMI ≥40 kg/m² (class III)

  • 2005-2006: 5.9%

  • 2017-2018: 9.0%

Almost three-quarters of Americans are overweight or obese, and 9% have severe (class III) obesity (BMI ≥40 kg/m²). The rates of obesity and severe obesity (sometimes known as morbid obesity) have steadily risen. In certain population groups, the obesity rates are markedly higher: during the survey period 2017-2018, about 50% of both Mexican-American men and women and 57% of non-Hispanic black women aged ≥20 years had a BMI ≥30 kg/m².[15]

Worldwide, it is estimated that nearly 4 million people die each year as a consequence of weight-related comorbidities; however, due to the varying influence obesity has on multiple comorbidities, it is difficult to truly quantify the full effect it may have on life expectancy.[16]

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