Is it possible to be overweight or obese and still be considered healthy? Most physicians advise their patients who are overweight or obese to lose weight because excess weight is a known risk factor for severe chronic diseases such as diabetes, high blood pressure or cardiovascular disease. However, in recent years, a controversy has arisen regarding the actual impact of increased weight on an individual’s life expectancy or risk of suffering from heart attacks. Some researchers argue that being overweight (body mass index between 25 and 30; calculate your body mass index here) or obese (body mass index greater than 30) primarily affects one’s metabolic health and it is the prolonged exposure to metabolic problems that in turn lead to cardiovascular disease or death.
According to this view, merely having excess weight is not dangerous. It only becomes a major problem if it causes metabolic problems such as high cholesterol levels, high blood sugar levels and diabetes or high blood pressure. This suggests that there is a weight/health spectrum which includes overweight or obese individuals with normal metabolic parameters who are not yet significantly impacted by the excess weight (“healthy overweight” and “healthy obesity”). The other end of the spectrum includes overweight and obese individuals who also have significant metabolic abnormalities due to the excess weight and these individuals are at a much higher risk for heart disease and death because of the metabolic problems.
Other researchers disagree with this view and propose that all excess weight is harmful, independent of whether the overweight or obese individuals have normal metabolic parameters. To resolve this controversy, researchers at the Mount Sinai Hospital and University of Toronto recently performed a meta-analysis and evaluated the data from major clinical studies comparing the mortality (risk of death) and heart disease (as defined by events such as heart attacks) in normal weight, overweight and obese individuals and grouping them by their metabolic health.
The study was recently published in the Annals of Internal Medicine (2014) as “Are Metabolically Healthy Overweight and Obesity Benign Conditions?: A Systematic Review and Meta-analysis” and provided data on six groups of individuals: 1) metabolically healthy and normal weight, 2) metabolically healthy and overweight, 3) metabolically healthy and obese, 4) metabolically unhealthy and normal weight, 5) metabolically unhealthy and overweight and 6) metabolically unhealthy and obese. The researchers could only include studies which had measured metabolic health (normal blood sugar, blood pressure, cholesterol, etc.) alongside with weight.
The first important finding was that metabolically healthy overweight individuals did NOT have a significantly higher risk of death and cardiovascular events when compared to metabolically healthy normal weight individuals. The researchers then analyzed the risk profile of the metabolically healthy obese individuals and found that their risk was 1.19-fold higher than the normal weight counterparts, but this slight increase in risk was not statistically significant. The confidence intervals were 0.98 to 1.38 and for this finding to be statistically significant, the lower confidence interval would have needed to be higher than 1.0 instead of 0.98.
The researchers then decided to exclude studies which did not provide at least 10 years of follow up data on the enrolled subjects. This new rule excluded studies which had shown no significant impact of obesity on survival. When the researchers now re-analyzed their data after the exclusions, they found that metabolically healthy obese individuals did have a statistically significant higher risk! Metabolically healthy obese subjects had a 1.24-fold higher risk, with a confidence interval of 1.02 to 1.55. The lower confidence interval was now a tick higher than the 1.0 threshold and thus statistically significant.
Another important finding was that among metabolically unhealthy individuals, all three groups (normal weight, overweight, obese) had a similar risk profile. Metabolically unhealthy normal weight subjects had a three-fold higher than metabolically healthy normal weight individuals. The metabolically unhealthy overweight and obese groups also had a roughly three—fold higher risk when compared to metabolically healthy counterparts. This means that metabolic parameters are far more important as predictors of cardiovascular health than just weight (compare the rather small 1.24-fold higher risk with the 3-fold higher risk).
Unfortunately, the authors of the study did not provide a comprehensive discussion of these findings. Instead, they conclude that there is no “healthy obesity” and suggest that all excess weight is bad, even if one is metabolically healthy. The discussion section of the paper glosses over the important finding that metabolically healthy overweight individuals do not have a higher risk. They also do not emphasize that even the purported effects of obesity in metabolically healthy individuals were only marginally significant. The editorial accompanying the paper is even more biased and carries the definitive title “ The Myth of Healthy Obesity”. “Myth” is a rather strong word considering the rather small impact of the individuals’ weight on their overall risk.
Some press reports also went along with the skewed interpretation presented by the study authors and the editorial.
A BBC article describing the results stated:
It has been argued that being overweight does not necessarily imply health risks if individuals remain healthy in other ways.
The research, published in Annals of Internal Medicine, contradicts this idea.
This BBC article conflates the terms overweight and obese, ignoring the fact that the study showed that metabolically healthy overweight individuals actually do not have a higher risk.
“The message here is pretty clear,” said the lead author, Dr. Caroline K. Kramer, a researcher at the University of Toronto. “The results are very consistent. It’s not O.K. to be obese. There is no such thing as healthy obesity.”
Suggesting that the message is “pretty clear” is somewhat overreaching. One of the key problems with using this meta-analysis to reach definitive conclusions about “healthy overweight” or “healthy obesity” is that the study authors and editorial equate increased risk with unhealthy. Definitions of what constitutes “health” or “disease” should be based on scientific parameters (biomarkers in the blood, functional assessments of cardiovascular health, etc.) and not just on increased risk. Men have an increased risk of dying from cardiovascular disease than women. Does this mean that being a healthy man is a myth? Another major weakness of the study was that there was no data included on regular exercise. Numerous studies have shown that regular exercise reduces the risk of cardiovascular events. It is quite possible that the mild increase in cardiovascular risk in the metabolically healthy obese group may be due, in part, to lower levels of exercise.
This study does not prove that healthy obesity is a “myth”. Overweight individuals with normal metabolic health do not yet have a significant elevation in their cardiovascular risk. At this stage, one can indeed be “overweight” as defined by one’s body mass index but still be considered “healthy” as long as all the other metabolic parameters are within the normal ranges and one abides by the general health recommendations such as avoiding tobacco, exercising regularly. If an overweight person progresses to becoming obese, he or she may be at slightly higher risk for cardiovascular events even if their metabolic health remains intact. The important take-home message from this study is that while obesity itself can be a risk factor for increased risk of cardiovascular disease, it is far more important to ensure metabolic health by controlling cholesterol levels, blood pressure, preventing diabetes and important additional interventions such as encouraging regular exercise instead of just focusing on an individual’s weight.
Kramer CK, Zinman B, & Retnakaran R (2013). Are metabolically healthy overweight and obesity benign conditions?: A systematic review and meta-analysis. Annals of internal medicine, 159 (11), 758-69 PMID: 24297192