Obesity definitions across media: social construction versus scientific fact

Definition of Obesity
The most common definition of obesity relates to the body mass index , or BMI. In the United States, the National Institutes of Health defines overweight as having a BMI of 25 or more, and obese as having a BMI of 30 or more. The BMI is basically a formula that relates one\\\\'s weight to one\\\\'s height (MedicineNet.com, 2018). The World Health Organization also uses the same definitions of overweight and obese (WHO, 2018). The operational definition of obesity can be broken down further, into Obese Level I, II, and III, each with higher BMI levels. A BMI over 40 is considered morbid obesity (MacMillan, 2018).
Credibility
While the definition of obesity using BMI is uniform, it is not without its faults. There are several critiques of BMI. One is that it does not take into account muscle mass (Janiszewski, 2012). This is true, of course, but it is a petty and weak rebuttal – the bodybuilder who is defined as obese is well aware that they are not obese. This argument provides, say, a former football lineman with an out to ignore health concerns stemming from their obesity, just because they have some muscle in there as well. But the logic is correct – BMI does not differentiate between muscle weight and fat weight.
Another critique of BMI is that it does not differentiate between the so-called apples and pears. BMI as a measure of obesity is fine, but the underlying assumption of examining obesity as a health issue is that there is a correlation between obesity and specific health outcomes. Body shape – where fat deposits on the body – has some correlation with health outcomes, and BMI does not differentiate in terms of overall body shape in its calculation. This reduces the effectiveness of BMI as a measure of obesity-related health outcomes (Janiszewski, 2012).
Janiszewski (2012) also argues that BMI does not always change in relation to lifestyle changes. A person can improve their health without changing their BMI. The critique is framed as though it invalidates BMI, but that\\\\'s a poor framing. The actual critique here is that BMI is not a perfect corollary for health, which any reasonable person would have understood from the beginning. That BMI is imperfect by no means invalidates it – unless there is actual scientific proof that it does.
Obesity as a Social Construction
The medical operationalization of obesity via BMI is not a social construction, but an attempt to understand the links between excess body fat and health outcomes. There is an informal social definition of obesity, but that is really in the eyes of the beholder. Any informal social definition of BMI is irrelevant to the discussion of obesity in the medical context.
References
Janiszewski, P. (2012) Why the Body Mass Index (BMI) is a poor measure of your health. PLOS. Retrieved February 18, 2018 from http://blogs.plos.org/obesitypanacea/2012/02/10/why-the-body-mass-index-bmi-is-a-poor-measure-of-your-health/

MacMillan, A. (2018) What is obesity? WebMD. Retrieved February 18, 2018 from https://www.webmd.com/diet/obesity/features/am-i-obese#1

MedicineNet.com (2018) Medical definition of obese. MedicineNet.com. Retrieved February 18, 2018 from https://www.medicinenet.com/script/main/art.asp?articlekey=11760

WHO (2018) Obesity and overweight. World Health Organization. Retrieved February 18, 2018 from http://www.who.int/mediacentre/factsheets/fs311/en/