The Puzzle of Adiposity and Health
If obesity is a disease simply defined by excess adiposity (body fat), then why is the puzzle of an obesity paradox so difficult to resolve? Why does it seem that some people with a high BMI might have better health outcomes in some situations that people with a lower BMI? The short answer is that BMI, a simple screen for excess adiposity, is far from being a perfectly sensitive and specific measure of it.
A new paper and companion commentary in Obesity provides important new insights. Gerben Hulsegge and colleagues tracked BMI along with measures of inflammation and oxidative (metabolic) stress across four generations. By following more than five thousand people for 15 years, they were able to show that a rising BMI predicted adverse changes in metabolic health, even for people whose BMI never rose above 25 – the level defined as a threshold for excess weight.
In the companion commentary, Antonis Vlassopoulos and Michael EJ Lean explain:
Cross-sectional data on BMI alone are unlikely to give a detailed picture of adiposity and changes in body composition changes across the life course. Longitudinal changes in body composition are always likely to be more sensitive predictors of morbidity and mortality. Populations with a BMI >25 kg/m2 might experience lower mortality rates (i.e., CVD mortality rate) if they maintain a stable (but elevated) BMI over the years.
In other words a snapshot of BMI might not say as much about metabolic health as a picture of changes in adiposity over time.
People who want to define obesity based upon arbitrary BMI benchmarks are missing the complexity of this disease. BMI is a pretty good screening tool, but it’s not the final word on body composition and metabolic health. And it’s only one marker for tracking clinical progress in obesity care.
Click here for the study by Hulsegge et al and here for the commentary by Vlassopoulos and Lean.
Lipid Bubbles, photograph © Thomas Lazzara / flickr
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May 9, 2016
May 09, 2016 at 8:56 am, Mary-Jo Overwater said:
How will this affect the epidemiological data we now use to record prevalence and incidence of obesity nationally and globally? Isn’t BMI used to define and classify obesity and overweight or are other criteria included. I don’t think so.
May 09, 2016 at 3:41 pm, Ted said:
I expect that for epi studies, BMI will continue to be the benchmark. For risk assessment, smart clinicians are already digging deeper.
May 10, 2016 at 8:04 pm, shelley kay said:
Individuals with high visceral adiposity and low muscle mass may have high, normal or low BMI. Older age, inactivity and disease may result in this phenotype. The use of waist circumference is a good predictor of metabolic risk due to its relationship with visceral adiposity independent of BMI, in fact, high waist circumference with low BMI represents arguably the worst phenotype representing disease in process and loss of muscle due to inflammation. The Health ABC study demonstrated that older adults with type 2 diabetes have accelerated loss of muscle compared to age matched healthy adults. Waist circumference, if measured well, is a good measure (not over clothes, no indentation, arms across chest, not above). Unfortunately, there are a number of protocols for WC (about 10) and they are not the same measure. There are even more protocols for waist-to-hip ratio. Health practitioners should know which protocol they are using and why according to the WC measure used to predict a cross sectional area of visceral adipose tissue that predicts metabolic risk. Subcutaneous adiposity provides a metabolic sink, a reservoir for lipid. When these adipocytes exceed their storage limit, lipid goes elsewhere, viscera, liver and muscle. In this scenario, higher BMI would offer some protectin. Inflammatory signals may change these healthier adipocytes and lead to adisopathy. BMI does not reveal where the fat is located, nor muscle and bone. In addition, exercise and physical activity improve metabolic function of good and bad adipocytes. BMI obscures all these important factors.
May 11, 2016 at 4:02 am, Ted said:
Shelley, thanks for your detailed and thoughtful comment.