An article by Susan Mayor of the British Medical Journal:

Obese people are at a greater risk of death and cardiovascular events even without metabolic abnormalities than people in the normal weight range, warns a study that questions the belief that it is possible to be healthy despite being seriously overweight (Kramer et al., 2013).

The systematic review and meta-analysis included observational studies published between 1950 and 2013 that evaluated mortality from all causes or cardiovascular events by body mass index and metabolic status, defined by components of the metabolic syndrome such as glucose tolerance and lipid profile.

The researchers analysed eight studies that met their criteria. These involved 61 386 patients and 3988 deaths or cardiovascular events.

Results for the four studies (with 23 209 patients) that had a follow-up period of 10 years or longer showed that metabolically healthy obese people have a 24% higher risk of all cause mortality or cardiovascular events than normal weight people with no metabolic risk factors (relative risk 1.24 (95% confidence interval 1.02 to 1.55)).

The study also showed that people of normal weight but with metabolic risk factors had an increased risk of events equal to that of metabolically unhealthy obese or overweight people (relative risks 3.14 (2.36 to 3.93) for normal weight, 2.70 (2.08 to 3.30) for overweight, and 2.65 (2.18 to 3.12) for obese people).

“Previous meta-analyses evaluating BMI and mortality have not considered the presence of metabolic factors,” pointed out the authors, led by Caroline Kramer, an endocrinologist at Mount Sinai Hospital, Toronto. “Our study shows that obese people are at increased risk for adverse long-term outcomes even in the absence of metabolic abnormalities, suggesting there is no healthy pattern of increased weight.”

They estimated that the absolute increased risk of 0.7% over 10-11 years associated with metabolically healthy obesity translated to 1.4 million deaths or cardiovascular events in the 200 million people thought to be in this category worldwide.

This risk made it worth while to comprehensively evaluate metabolic factors as well as BMI for predicting future morbidity and mortality, the researchers suggested. They speculated that people who were metabolically healthy but obese probably had subclinical levels of risk factors and that vascular dysfunction would worsen over time.

In an accompanying editorial James Hill and Holly Wyatt, of the Anschutz Health and Wellness Center, University of Colorado, Aurora, argued that the findings indicated a need to treat obesity, regardless of metabolic risk factors, like any other chronic disease to reduce the long term risk of death and cardiovascular events (Hill & Wyatt, 2013).

Source

BMJ 1013;347:f7324.

References

Kramer, C.K., Zinman, B. & Retnakaran, R. (2013) Are Metabolically Healthy Overweight and Obesity Benign Conditions? A Systematic Review and Meta-analysis. Annals of Internal Medicine. 159, pp.758-769.

Hill, J.O. & Wyatt, H.R. (2013) The Myth of Healthy Obesity. Annals of Internal Medicine. 159, pp.789-790.