Body Mass Index as Measure of Metabolic Health: One Size May Not Fit All
A Message from Dr. Christopher Still
Christopher Still, DO, FACN, FACP, Co-Clinical Editor, Bariatric Times; Medical Director for the Center for Nutrition and Weight Management, and Director for Geisinger Obesity Research Institute, Geisinger Medical Center, Danville, Pennsylvania. Dr. Still is also a board member of the Obesity Action Coalition, Tampa, Florida.
Dear Colleagues,
I’m pleased and honored to address you alongside my dear friend and colleague Dr. Alan Wittgrove. I’m also excited to discuss a topic that has been getting a lot of attention in the press and on social media—BMI.
The use of body mass index (BMI) to define obesity and metabolic health has been a popular talking point in our field for years. Recently, this debate swelled further when a study by Padwal et al published in the Annals of Internal Medicine[1] that examined BMI and body fat percentage concluded the following: Low BMI and high body fat percentage are independently associated with increased mortality.
Though the study has a few limitations (e.g., variables of physical activity and smoking were unavailable), it shows that to get the full picture of a person’s metabolic health, we need to consider other, more defining parameters like body fat percentage, which is measured using dual-energy x-ray absorptiometry (DXA). We might also examine cardiovascular markers—low-density lipoprotein [LDL], high-density lipoproteins [HDL], total cholesterol, and C-reative protein (CRP). I would add that it is also important to look at waist circumference and how an individual carries weight—in the midsection (“apple-shaped”) or hips (“pear-shaped”).
Another recent study[2] evaluated the relationship between adiposity indices (a body shape index [ABSI] and body adiposity index [BAI]), and mortality in 77,505 postmenopausal women. Their findings were similar to Padwal et al: ABSI appears to be a clinically useful measure for estimating mortality risk, perhaps more so than BAI and BMI. I personally think waist circumference is important to measure.
The main message of both of these studies is that an individual’s BMI is not the only predictor of metabolic health. You can examine two people with the same BMI and find two very different health profiles. Someone can be at risk of developing comorbidities, such as type 2 diabetes mellitus and hypertension, at BMIs lower than those that define the stages obesity. The reverse is also true. A person with obesity according to BMI might actually prove to be metabolically healthy.
From a research standpoint, it would be interesting to investigate these two ends of the spectrum further. We might ask the following: 1) What are the characteristics of the unique set of individuals that have high BMIs but no metabolic syndrome? They seem be protected in some way, whether due to body fat percentage, genetics, or other factors Answering these questions could help us better understand and treat the disease.
While I agree that the BMI is not a perfect measure, I do feel it still plays an important role in our field, serving as a good starting point for analyzing overall risk stratification in large cohorts. You have to be able to compare apples to apples. Oftentimes, you don’t have body fat percentage and/or waist circumference measurements on a cohort, so the next best thing, though it may not be sensitive or specific, is BMI. It’s also more easily attainable than other measures because it’s regularly collected data.
Another important point in the discussion on abandoning BMI: many wellness programs and insurance companies rely on it. The stages of obesity and, therefore eligibility for bariatric surgery are defined by BMI. I think there are likely people at higher risk for morbidity and mortality based on measures beyond BMI, which are being explored in recent research that would benefit from bariatric surgery. But changing treatment standards would require more data on treatment intervention and outcomes in patients at all ends of the BMI spectrum. Integrative health systems like Geisinger are capable of collecting this data. I think this means we have obligation to our field to find these answers through research.
Instead of being an absolute definition of metabolic health, maybe we should look at BMI as merely a screening tool. For instance, individuals with BMIs in a certain range (e.g., 25kg/m2 and over) are identified as potentially being at risk for increased metabolic issues. From there, we can embark on a more personalized approach—precision medicine based on the individual’s makeup.
So, what do you think? I invite you to share your thoughts in a letter to the editor. We would love to hear from you.
Sincerely,
Christopher Still, DO, FACN, FACP
References
1. Padwal R, Leslie WD, Lix LM, Majumdar SR. Relationship Among Body Fat Percentage, Body Mass Index, and All-Cause Mortality: A Cohort Study. Ann Intern Med. 2016 Mar 8. [Epub ahead of print]
2. Thomson CA, Garcia DO, Wertheim BC, et al. Body shape, adiposity index, and mortality in postmenopausal women: Findings from the Women’s Health Initiative. Obesity (Silver Spring). 2016 Mar 15. [Epub ahead of print]
Category: Editorial Message, Past Articles
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