Q&A Series: Should We Care About BMI?

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In our Q&A series we’ve unpacked the paleo diet, the gluten-free dietcleanses, and yoga therapy. This week, Kayla Walker, MFT Intern, spoke with Megan Holt, MPH, RD, Potentia’s Coordinator of Nutrition and Wellness to learn about using BMI as an indicator of health.

Note from Rebecca: The following post may be triggering for some who are early in their recovery or struggling with their recovery, so please pause here if this information will not be helpful for you right now. There is some frank talk about numbers in this post because we want to offer some accurate information about the BMI, what it is, why it is not an accurate or helpful indicator of health and how its use is fueling the disordered eating spectrum.

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Kayla: What is BMI?

Megan: BMI stands for body mass index. It’s an equation commonly used in healthcare venues to estimate risk of developing chronic diseases that often accompany increases in body fat, such as diabetes, heart disease, and many forms of cancer.

Kayla: How do you calculate BMI? How do you know whether your BMI is in a healthy range?

Megan: The formula for BMI is:

BMI = weight in pounds/(height in inches x height in inches) x 703
or
BMI = weight in kilograms/height in meters squared

CDC recommendations categorize BMI in ranges of underweight, ideal weight, overweight, and obese, as follows:

Below 18.5 = Underweight
18.5 to 24.9 = Ideal
25.0 to 29.9 = Overweight
30.0 and above = Obese

Note from Rebecca: In 1998, the FDA changed the ranges for the BMI and overnight millions of people became “overweight” and “obese.” In his movie America the Beautiful, Darryl Roberts noted this changed was approved by a board that was directly connected to the dieting industry. Given the annual 50+ billion dollars which are spent on diets and diet related products, the BMI is regularly used as a marketing tool to support the use of various products in this industry. And since diets do not work – and in fact set you up to regain the weight and often more within 1-2 years – it seems the BMI is more of a marketing tool than a predictor of true health.

Kayla: Where did the idea of using BMI as a marker of health originate?

Megan: A mathematician (not a clinician) from Belgium by the name of Lambert Adolphe Jacques Quetelet came up with the BMI in the early 1800’s. His aim was to come up with an inexpensive proxy for measuring degree of obesity. Named the Quetelet index (and later BMI), it was used as a means of assessing “appropriateness” of weight for height.

Kayla: Why is BMI used?

Megan: After WWII it was noted that obese and overweight life insurance policy holders were at higher risk for morbidity and mortality were getting increasingly fatter.

It’s easy to understand and compute, it’s inexpensive, and gives us some helpful feedback in terms of anthropometric assessment, though this holds true mainly in the extremes (very underweight and very overweight/obese).

Note from Rebecca: Recent studies are showing a lower death risk for those who are considered “overweight” according to the BMI  furthering doubt the BMI ranges are not helpful in indicating true health.

Kayla: What are the limitations of using BMI as a marker of health?

Megan: BMI does not account for differences in bone mass/structure, fat mass and lean body (muscle) mass, nor where fat is stored (visceral vs. subcutaneous).

Visceral fat (fat around the abdomen/vital organs) is much more inflammatory and problematic in terms of health risks than subcutaneous fat (under the skin).

It implies that thin or normal weight individuals are healthy and have lower risk of developing preventable disease relative to their overweight (according to BMI) counterparts, and this just isn’t the case.

Athletes are an excellent example of persons who tend to have higher BMI’s but carry lower disease risk. Similarly, body fat is underestimated in the elderly, as they typically carry very little lean body (muscle) mass. Remember, one can be thin and simultaneously unfit and/or unhealthy.

Kayla: What should we be using instead, or at least in conjunction with BMI, to predict health risks? What are other markers of health?

Megan: Waist to hip ratio, for one, needs only a measuring tape, and has more predictive power than BMI. Women should have a waist-to-hip ratio of 0.8 or less, and men 0.95 or less. Women are advantageously pear shaped, and thus carry lower risk for preventable diseases. Think of this next time you’re cursing your curves, and please STOP hating on your body!

Other methods exist that are quite costly and/or intrusive, but may be more accurate, such as requesting a lipid panel (which requires blood work) from your physician, or assessing body fat through use of skin fold calipers, underwater weighing, or bioelectrical impedance. However, assessment of percent body fat alone still does not account for ‘location’ of fat-visceral versus subcutaneous.

Kayla: How do you assess your clients? Do you use BMI as a health indicator?

Megan: I rarely, if ever, calculate BMI when working with clients, whether they are athletes or people struggling with disordered eating.

Rather, I use an assessment of their current diet and lifestyle behaviors and blood work results from their physician to measure risk.

When working with individuals who do fall in the extremely obese category, I find that they are well aware of where they fall in terms of BMI categories, and that calling attention to this is not helpful.In fact, it often deters these individuals from wanting to make changes to lifestyle, as they likely will remain in the ‘obese’ category even with a fairly significant weight loss.

We know that even mild weight loss, 5-10%, for example, is enough to significantly decrease risk of “Western” diseases, such as diabetes, heart disease, and numerous cancers.

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Thanks for reading our Q&A on BMI!

What are your thoughts about using BMI as an indicator of health? Has it been helpful or harmful in your journey to health? What additional questions do you have about health, weight, or body image?

We would love to hear from you and address your questions on health and wellness in a future Q&A blog post.

In good health –

Kayla & Megan