Why Body Mass Index (BMI) is not a measure of health

Updated: Oct 28



In the article, What’s wrong with the ‘War on Obesity?’ the authors state, “by all measures, the BMI is an extremely poor test to be used as a basis for public health policy and clinical interventions.” Evidence from the literature does not support this claim that having a body weight above the ‘healthy weight’ BMI category will result in poorer life expectancy.


The opposite leans closer to the truth. The claim that life expectancy is reduced as a direct result of body weight higher than the normal weight BMI category is not supported by large epidemiological studies. Currently life expectancy is the primary health indicator used at the population level. Research indicated that the highest life expectancy (following 1.8 million people over a 10-year period) was in people with a BMI between 26 and 28 the ‘overweight’ BMI category. Those with the lowest life expectancy had a BMI of under 18 the ‘underweight’ BMI category. Lastly, those with a BMI between 18 and 20 in the ‘healthy weight’ BMI category had a lower life expectancy than those with a BMI between 34 and 36 in the ‘obese’ BMI category.


Clearly BMI is not a measure of health; it does not differentiate between lifestage, gender, body composition, muscle mass or wasting, bone density, hydration status, cultural differences, distribution of body fat stores, frame size or psychological considerations such as trauma, stress or stigma.


The body mass index was never designed to be a marker of health in individuals but was originally designed for populations. It is a weight-to-height ratio that is calculated by dividing one’s weight in kilograms by the square of one’s height in meters and was developed in the 1800’s by a Belgian statistician Adolphe Quetelet. In addition the formula was based only on white males and ignores all other nationalities, health behaviors and other factors that contribute to a person’s health status.


Who advised the BMI weight categories?


The World Health Organization (WHO) relied on the International Obesity Task Force (IOTF) to make the recommendations for weight classifications indicating- obese, overweight, normal, and underweight. Interestingly, it has been called out in continuing education platforms, that at that time, the two biggest funders of the IOTF were the pharmaceutical companies that had the only weight-loss drugs on the market.


Why is BMI still used?


Currently BMI is used to determine levels of care when working with individuals in recovery from eating disorders and to determine severity of Anorexia Nervosa in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). BMI is also still used by some health insurance companies to determine weight goals.


Nutrition Intervention for Eating Disorders by the Academy of Nutrition and Dietetics reports “weight alone does not indicate health or recovery” and suggests that an ideal weight is variable for each individual and is maintained without the presence of purging, eating disorder behaviors and where blood pressure, body temperature, heart rate and reproductive function

are within normal limits.


It’s also important to acknowledge that higher weight is correlated with certain health conditions, but higher weight is not the sole cause of health detriments. Causal factors are closer tied to weight-based stigma resulting in physiological effects in the body such as higher blood pressure, type 2 diabetes, metabolic syndrome, cortisol reactivity and oxidative stress.


What now?


A movement towards a paradigm shift in weight science and evidence supporting Health at Every Size® HAES® has arrived. Health at Every Size® “does not propose that people are automatically healthy at any size, but all people deserve fair access to opportunities and environmental conditions that will enhance their health and well-being, irrespective of their body size.” HAES® identifies that weight gain alone is not a health risk factor but weight cycling (yo-yo dieting) is strongly associated with negative health outcomes.


Lastly, the authors of What’s wrong with the ‘War on Obesity?’ conclude that “weight loss is not only almost impossible for most people to maintain, but attempted weight loss strongly predicts weight gain.”


Stay tuned to learn more about the Health at Every Size® Principles.


Check out this brief animated video titled ‘Poodle Science’ by the Association for Size Diversity and Health (ASDAH) that exposes the limitations of current research on weight and health.


https://www.youtube.com/watch?v=H89QQfXtc-k




References:


Poodle Science video- Association for Size Diversity and Health (ASDAH); https://www.youtube.com/watch?v=H89QQfXtc-k


Bacon, L., Aphramor, L. Weight Science: Evaluating the Evidence for a Paradigm Shift. Nutr J 10, 9 (2011).

https://doi.org/10.1186/1475-2891-10-9

https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-10-9


Moynihan R. Obesity task force linked to WHO takes "millions" from drug firms. BMJ. 2006;332(7555):1412. doi:10.1136/bmj.332.7555.1412-a

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1479667/


O’Hara, L., Taylor, J. What’s wrong with the ‘War on Obesity?’ A narrative Review of the Weight-Centered Health Paradigm and Development of the 3C Framework to Build Critical Competency for a Paradigm Shift. Sage 8,2 (2018). https://doi.org/10.1177/2158244018772888


Academy of Nutrition and Dietetics Pocket Guide to Eating Disorders, 2nd Edition (2017)


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