Why BMI Might Be BS
Holley Samuel RD, LDN, CPT
Let’s chat about body mass index (BMI) and weight because this subject comes up in nearly every beginning session I have with my clients at my practice.
Has anyone ever felt personally victimized by weight, clothing sizes, BMI or anyone who holds those as a standard of any kind? I bet most of you are virtually raising your hands. Hear me out!
BMI and weight are easy measurements to take on people- just step on a scale and measure your height! Blood work, mental health, and emotional well-being are a lot harder to measure. We often tend to focus on things as a society and in health care that we can easily measure, which produces very black and white thinking. There is nothing wrong with measuring weight and BMI to use as a data point, but when it becomes the only data point or determinant of any outcome, we have focused too much on just a tiny piece of the picture. We do not go around focusing on height being a cause of conditions like diabetes and cardiovascular disease, so why is weight of such significant interest or even an obsession for some?
We certainly have adopted a fatphobic mindset in this country, which is toxic to those living in larger bodies who are experiencing this stigma- and according to data, that’s at least 1/3 of the country’s population. Not to mention that this fatphobia is also rooted in white supremacy, and poorly acknowledges diverse body colors, sizes, and shapes or even deems them “below standard” or “inappropriate.” We are taught that certain cultures are more prone to diseases such as cardiovascular disease or diabetes but are never taught why- one reason being because of socioeconomic factors rooted in systemic racism, which has not really anything to do with biology. I will be the first to say that I benefit in countless ways from the thin, white body frame that my genetics have given me. Yes I live an objectively healthy lifestyle currently, but that really has little to do with my appearance as an outcome. I will be the first to say that it does not matter what you look like- you can still experience negative self talk and poor self acceptance, and for this reason (which is one of many) it is important to address mental and emotional health BUT that does not take away from the privilege I have and others who look like me have on a daily basis, because white and thin is how I am likely perceived by most people, personal challenges aside. In my experience in practice as a dietitian and personal trainer, two people who put in a lot of effort to workout and eat in the exact same ways can still weigh different weights by literally hundreds of pounds. This would be like asking two people of different heights to wear the same shoe and expect them to now be the same height and healthier for it. This makes no sense. These are all topics that deserve elaboration and detail in another series of blog posts, but it is crucial that I bring them up in this one.
First, BMI is outdated (1830s!) and a terrible determinant of health for the way our modern society uses it in this country. BMI is a height for weight ratio (kg/m2), and the truth is we use it to this day in 2020 because it is easy and cheap to measure. In fact, one long term study shows that those who change their BMI over the course of their life (whether it got larger or smaller- and you can pretty much only significantly change your BMI if you change your weight since it is challenging to purposefully change your height as an adult) are more likely to be at risk for developing chronic illness like ️cardiovascular disease than those who stay the same BMI throughout their life. The BMI itself and whichever category didn’t matter, and multiple categories were represented.
Actually, in another study, about 30% of individuals with a BMI in the “healthy” range were found to develop chronic illness like cardiovascular disease while about 30% of individuals with a BMI in the “obese” category were perfectly healthy. This study used other health related measurements like blood work to determine health status. Blood work is something I prefer to use with my clients in my practice to take a bigger picture view of health status in conjunction with other measurements like blood pressure, menstrual cycle details and status in females, sleep quality and adequacy, weight and body composition patterns rather than singular measurements, perceived level of exertion in exercise or energy levels in general, client dietary habits and relationship with food and their body image, and overall client feedback. These factors of course are much more difficult to measure than asking “what do you weigh” or having someone step on a scale real quick in an office visit. Actually I have seen many times that when a client gets weighed, it changes the outcome of the entire appointment encounter- either for better or for worse depending on the number and what the client wanted the number to be. How stressful and unproductive! This is a poor way to build trust with clients as a health care provider, in my opinion and through research.
Another study shows that a Health At Every Size (HAES) approach not centered around weight when combined with an appropriate exercise program improved mental and physical health significantly more than a weight loss approach alone. Participants in the study had lower dropout rates than many other weight loss studies, found it empowering to exercise regardless of their current weight and with no future “goal weight” in mind, and were overall mentally and physically healthier as a result shown in the study outcomes.
No long term studies (long term meaning about 5-10 years or longer) show that weight loss on its own improves health or that weight loss is sustainable long term. In fact, a meta-analysis of 29 various weight studies show that at least 80% of participants regained the weight they lost on various diets within 5 years (and some gained back even more weight than they lost). This analysis shows that going on a diet is actually a strong predictor of future weight gain. Since diets predict weight gain, yet we prescribe them to at least 1/3 of our country’s population who have BMIs that are not “acceptable” to diet culture (even though many of these individuals are actually perfectly healthy when other data are collected to support this, while many of those who are an “acceptable” BMI are NOT healthy when other data is collected), knowing that at least 80% of those people will regain the weight or more, and that changing BMI is actually connected to poor health outcomes in some cases, why are we still doing this? Why are we blaming “the obesity epidemic” costing the health care system more money when the dieting industry that’s prescribed to “fix it” is making over $72 billion per year?
The media in the weight loss industry want you to be saying “well for me it’ll be different!” right now to yourself, but you can’t out-will your biology. So why not start working WITH your biology? Instead of focusing on weight as a determinant of your health and trying to manipulate the number on the scale in the name of health, perhaps learning how to change your behaviors and lifestyle habits to support your overall health is a more rewarding and productive place to start. Weight is a symptom or outcome of other things, and often not a root cause.
Want to use an approach that actually works long term and makes you feel good about yourself while doing it? Check out my programs!
I am a registered dietitian nutritionist, certified personal trainer, and owner of this private virtual nutrition and fitness coaching practice, Holley Fueled Nutrition LLC. I specialize in helping all levels of runners train for races, develop a healthy relationship with food and body image, and fuel themselves for optimal performance both in running and life in general. I enjoy running and endurance sports, riding horses, hiking, swimming, paddle boarding, yoga- pretty much anything outdoors! I went from non-runner throughout high school and college to Boston Qualifier coached by myself, taking 35 minutes off my marathon time between my first and second marathons. I have been an endurance junky ever since!
References
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
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
Lloyd-Jones, D. M. , Liu, K. , Colangelo, L. A. , Yan, L. L. , Klein, L. , Loria, C. M. , Lewis, C. E. & Savage, P. (2007). Consistently Stable or Decreased Body Mass Index in Young Adulthood and Longitudinal Changes in Metabolic Syndrome Components. Circulation, 115(8), 1004-1011. doi: 10.1161/CIRCULATIONAHA.106.648642.
Ltd, R. (n.d.). The U.S. Weight Loss & Diet Control Market. Retrieved August 07, 2020, from https://www.researchandmarkets.com/research/qm2gts/the_72_billion?w=4
Penney, T. L., & Kirk, S. F. (2015). The Health at Every Size paradigm and obesity: missing empirical evidence may help push the reframing obesity debate forward. American journal of public health, 105(5), e38–e42. https://doi.org/10.2105/AJPH.2015.302552
Ulian, M. D., Pinto, A. J., Sato, P. de M., Benatti, F. B., Campos-Ferraz, P. L. de, Coelho, … Scagliusi, F. B. (2018, July 6). Effects of a new intervention based on the Health at Every Size approach for the management of obesity: The "Health and Wellness in Obesity" study. Retrieved August 5, 2020, from https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0198401#abstract0