Regular readers will have followed the track of studies demonstrating that BMI is but a poor measure of health. This is why we came up with the Edmonton Obesity Staging System, that defines obesity based on the actual presence of physical, mental, and/or functional problems and limitations. Readers will recall, that we have previously shown that Obesity Stage – in contrast to BMI – is a powerful predictor of CV and all-cause mortality.
Now, yet another study, which looks at the relationship between BMI and mortality, again shows that ‘metabolically healthy’ obese individuals do not have an increased risk for CV mortality and in fact have a lower risk than ‘metabolically unhealthy’ non-obese individuals.
This study by Mark Hamer and Emmanuel Stamatakis from University College London, UK, published in the Journal of Clinical Endocrinology and Metabolism, looks at data from an observational study with prospective linkage to mortality records in community-dwelling adults from the general population in Scotland and England.
The sample includes 22,203 men and women [aged 54.1 y, 45.2% men] without known history of CVD at baseline followed for an average of about 7 years.
Based on blood pressure, high-density lipoprotein-cholesterol, diabetes diagnosis, waist circumference, and low-grade inflammation (C-reactive protein ≥ 3 mg/liter), participants were classified as metabolically healthy (0 or 1 metabolic abnormality) or unhealthy (two or more metabolic abnormalities). Obesity was defined as a body mass index of 30 or greater.
Compared with the metabolically healthy nonobese participants (about 20% of the obese population), their obese counterparts were not at elevated risk of CVD or all cause mortality.
On the other hand, both non-obese and obese participants with two or more metabolic abnormalities were at elevated risk.
Not surprisingly, metabolically unhealthy obese participants were at elevated risk of all-cause mortality compared with their metabolically healthy obese counterparts.
These data fit nicely with our findings using the obesity staging system. Thus, in our studies of the NHANES and Cooper Longitudinal Fitness Study, we found that Stage 0 and 1 obese individual (i.e. those with no or pre-clinical risk factors) did not have an increase risk compared to Stage 2+ individuals (those with comorbidities and/or endorgan damage).
Consistent with the present study, we also found that about 50% of non-obese individuals (in the BMI 25-30 range), would in fact fall into the Stage 2+ categories based on metabolic or other abnormalities.
Thus, simply using BMI as an indication for treatment would ‘over treat’ a substantial number of ‘obese’ individuals while missing an even greater number of ‘non-obese’ individuals, who are at risk.
As pointed out in an accompanying editorial by JP Després,
“Thus, obesity assessed by the BMI cannot properly estimate CVD and all-cause mortality risk. Furthermore, the therapeutic objective of achieving a normal BMI to prevent/manage cardiometabolic diseases may also be questioned on the basis of the emerging evidence…..The study by Hamer and Stamatakis provides robust evidence that a paradigm shift is needed: obesity can no longer be assessed the old-fashioned way.”
This is why the 5As of Obesity Management recommend the assessment of Obesity Stage in addition to BMI prior to giving patients any advice on managing their weight.
Hamer M, & Stamatakis E (2012). Metabolically healthy obesity and risk of all-cause and cardiovascular disease mortality. The Journal of clinical endocrinology and metabolism, 97 (7), 2482-8 PMID: 22508708
Després JP (2012). What is “metabolically healthy obesity”?: from epidemiology to pathophysiological insights. The Journal of clinical endocrinology and metabolism, 97 (7), 2283-5 PMID: 22774209.