Moving past assumption: Body mass index as an indicator of obesity
With the growing continuum of health risks associated with being overweight and obese, international guidelines were advocated to determine health, weight loss interventions, pharmacologic treatment, and bariatric surgery. We mainly reply on a body mass index (BMI) cut-off point to define overweight and obesity. However, the appropriate BMI cut-off points to define overweight and obesity that are associated with increased mortality risk is controversial. WHO defines BMI between 25.00 and 29.9 kg/m2 as overweight and ≥ 30.00 kg/m2 as obese. However, these cut-off points have been derived mainly from Western populations and there is considerable concern that this cut-off for BMI is not applicable across ethnic groups, especially among diverse Asian populations. Evidently, there is an increased cardiometabolic/vascular disease risk at even lower BMI cut-off points for South Asian populations. Accordingly, the BMI cut-off point of 23.0– 24.9 and ≥ 25.0 kg/m2 have been recommended for Asian populations for defining overweight and obese, respectively.
The concept of duality of cut-off points for defining overweight and obesity for universal use and individual country use could be looked at in terms of one cut-off for morbidity and mortality statistics and the other to define the cardio-metabolic/vascular disease risk. Studies in South Asians have shown higher mortality risk at BMI ≥25 kg/m2 but fail to show inordinately high mortality at BMI cut-points ≥ 23 kg/m2. Thus, the validity of cut-off points ≥ 23 kg/m2 has been questioned because of the lack of robust data, particularly in the context of mortality. Further, the WHO Expert Consultation report in 2004, recommended maintaining the original cut-off values (WHO, 1995) as universal definitions since available data do not necessarily indicate a clear BMI cut-off point for all Asians for overweight or obesity and no attempt was made to redefine the cut-off points for each population separately. In addition, the WHO Consultation proposed that countries could make decisions about the definitions of increased risk for their populations.
Though BMI has been accepted as a satisfactory index of underweight and obesity, it cannot alone be used to identify the distribution of adipose (Body Fat Mass (BFM)) and lean mass (fat-free mass (FFM)) components of body composition making it difficult to disentangle the role of adipose and lean mass in associations of BMI with health outcomes. Also, BMI does not truly reflect the health risk in the population. Some individuals can have a normal BMI but a high body fat percentage known as normal weight obesity. A person who has normal weight obesity could be just as unhealthy as someone with a high BMI. Also, based on BMI cut-off we have equated lower weight with better health and often labelled weight loss goals to the standardized BMI ranges, which do not take into account the adipose (BFM) and lean mass (FFM) components of body composition nor how they are achieved. Also, the body positivity movement has gained tremendous pop-culture attention at present which echoed the shift in perception where we are moving out of the era of looking at a person and determining if they are healthy leading to an expanded definition of beauty based on BMI cut-off (Pak, 2020). Regardless of the fallacies of BMI, obesity and its association with a continuum of health risks cannot be ignored. Due to the health risk associated with obesity, efforts have been made to properly quantify body fat in individuals and in different populations. This call for an alternative measure of body composition as an indicator of health or obesity.