Decoding the BMI Scale and Understanding Weight Stigma

What is BMI?

BMI, or ‘body mass index’, is a proportion (BMI = mass (kg)/height (m2)) that has become engrained in our healthcare system. The scale puts people in categories (underweight, overweight, obese) based on their proximity to the average or ‘normal’. As this number continues to be used to label people in terms of their weight status and overall health risk, it’s important to remember what BMI really tells us and acknowledge its shortcomings.

The origin of the BMI scale

Formerly known as the Quetelet Index, the scale was developed in 1832 by a Belgian mathematician Lambert Quetelet who was interested in characterizing the ‘average man’ at the center of a data set. In 1972, a scientist and nutrition researcher named Ancel Keys popularized the Quetelet Index as ‘the Body Mass Index’.1 However, Keys explicitly states that BMI has limitations when it is applied to the individual stating, “Average values for weight and height for given age and sex for a given population do not necessarily apply to other populations or even to the same population at another time.”1

The limitations of the BMI scale

Remember, BMI only accounts for weight and height. It doesn’t account for several other important indicators of health including age, gender, race/ethnicity, lean body mass, fat mass, lifestyle, or socioeconomic status. In addition to these obvious shortcomings, the nearly 200-year-old data that was used to develop BMI was collected from primarily Caucasian men, meaning that a ‘normal’ BMI is actually representative of an average white man and is likely less accurate when it is extrapolated to people of a different age, gender, or ethnicity. 

Contemporary research supports the notion that BMI is not generalizable. A 2019 study found that health risk manifests at a lower BMI amongst Korean males compared to the traditional BMI scale.2 Another study found that at the same BMI an Asian person tends to have 3-5% more adipose tissue than a white person and a black person tends to have less adipose tissue and more muscle mass.3

Weight stigma

Weight stigma is defined as negative beliefs, experiences and discrimination projected upon an individual based on body weight.4 Examples of weight stigma include the idea that weight gain is a choice as well as common negative assumptions about people in larger bodies regarding their willpower, their compliance, or their intelligence. Unfortunately, BMI is fueling weight stigma as people are quickly put into a weight category at first glance.

The impact of weight stigma

A hyper focus on weight by healthcare practitioners can result in behaviors that are harmful to health, neglect of the true root causes of a condition, misdiagnosis, and lower quality patient care. Weight stigma can also have a number of mental and emotional effects on patients such as stress, anxiety, depression, poor body image, distrust with a provider, and discouragement from seeking preventative care.4,5

Research has shown weight stigma leads to higher risk of physical and mental health problems such as eating disorders, low self-esteem, and anxiety and major depressive disorder. Problematic behaviors such as substance abuse, weight cycling, social isolation, and avoidance of exercise are also common amongst people who have experienced weight stigma.4,5

What you can do

If you feel that you are being negatively affected by weight stigma, consider having a conversation with your providers about your feelings on weight and suggest that you focus on improving other indicators of health in your life such as your dietary patterns, your physical activity level, your lab values, or your mental and emotional health. If you are interested in adding more weight-sensitive providers to your care team, consider seeking out providers who are aligned with Health At Every Size (HAES). These professionals have pledged to treat people of all body sizes with dignity and respect. A Registered Dietitian who is HAES aligned and trained in Intuitive Eating will also be a great ally on your health journey.

  1. Keys A, Fidanza F, Karvonen MJ, Kimura N, Taylor HL. Indices of relative weight and obesity. Int J Epidemiol. 2014;43(3):655-665.
  2. Hood K, Ashcraft J, Watts K, et al. Allometric scaling of weight to height and resulting body mass index thresholds in two Asian populations. Nutr Diabetes. 2019;9(1):2.
  3. Health HTHCSoP. Ethnic Differences in BMI and Disease Risk. Accessed February 25, 2022, 2022.
  4. C. P, S. Y, S. FC. Weight stigma and its impact on paediatric care. Curr Opin Endocrinol Diabetes Obes. 2019.
  5. Rubino F, Puhl RM, Cummings DE, et al. Joint international consensus statement for ending stigma of obesity. Nat Med. 2020;26(4):485-497.

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