Introduction
Epidemiology
Obesity is a complex multifactorial disorder, which has reached epidemic proportions worldwide. It affects all aspects of an individual’s life: physical, social, emotional, and psychological.
Although it is largely preventable, obesity is now a major public health issue, being associated with chronic illnesses such as type 2 diabetes, cardiovascular disease, depression, disability, and some cancers (1). Overweight and obese individuals now make up approximately one- third of the world’s population (2). Obesity has been coined the ‘reproductive hurdle’ as pregnancy in an obese woman is associated with multiple adverse outcomes such as congenital abnormalities, gestational diabetes, stillbirth, and higher caesarean section rates (3, 4). It also has far-reaching sequelae for the offspring as a consequence of being exposed to the in utero environment of an obese mother (5). Pregnant obese women have a higher incremental cost of antenatal and intrapartum care (6). It has been estimated that the toll of obesity on healthcare systems alone is between 2% and 7% of all healthcare spending in developed countries (7).The classification of obesity is based on the body mass index (BMI) and is expressed as weight in kilograms over the height (in metres) squared (Table 7.1). The definitions, however, remain controversial. The current ‘normal’ BMI was a compromise reached by the World Health Organization (WHO) when it was recognized that in the United States, higher BMIs are considered ‘normal’ (8).
There are strong advocates of tightening the WHO classifications further according to the population assessed. A WHO Expert Consultation in 2004 assessed scientific data suggesting that Asian populations have different associations between health risk, BMI, and body fat percentage (9). This report concluded that Asians have a higher risk of comorbidities at lower BMI compared to Caucasians.
They found that obesity-related disease, particularly type 2 diabetes and cardiovascular disease, occurred at a higher rate even at the normal BMI (25 kg/m2) cut-off by the WHO standards. As a consequence, the report concluded that in these populations the normal BMI should be limited to 18.5-22.9 kg/nff. In Japan, obesity is now defined as a BMI value greater than 25 and in China the bar is set at a BMI value of 28 (10, 11). For simplicity, the current BMI is calculated the same for men and women over the age of 18 years. In the under 18 years age group, sex- and BMI-specific measures are used. However, again the cut-offs are arbitrary.Although initially identified as an epidemic in the United States and Europe, obesity is not just an epidemic of the Western world. It is no longer associated only with affluence but occurs in lower socioeconomic groups and the developing world (12-14). In 2010, worldwide 11.5% of adults were obese compared with 13% in 2014 (15). An incremental rise in obesity since 1980 in all age groups irrespective of gross domestic product, especially among adolescents in both sex groups, has been reported by Ng et al. (16).
As defined earlier, obesity is more prevalent in women (14%) than in men (10%) although there is no difference at the overweight stage (17). In comparison to men, women also disproportionately represent the extreme obesity groups (BMI ≥35 kg/mff) regardless of age or ethnicity. Rural women in Europe are more likely to be obese whereas in Africa, women living in urban areas are more obese. The prevalence of obesity can be significantly different even within different parts of the same country (12).
There is concern that although the prevalence of adult obesity in developed countries is stabilizing to one in three, the prevalence among children and adolescents is rising (14). Obese children are at risk of chronic illness and mortality as obese adults, but worryingly, these also occur with premature onset or earlier in adulthood.