The Lancet Diabetes & Endocrinology: What exactly is healthy obesity?

Metabolically healthy obesity – where an individual has a Body Mass Index (BMI) greater than 30, but does not appear to be at increased risk of the health complications usually associated with excess weight – has only been recently widely recognised by medical practitioners. But as global levels of obesity continue to rise, identifying metabolically healthy obese patients could be of critical importance in ensuring that patients are given appropriate, and cost-effective, treatment, say the authors of a Viewpoint, published in "The Lancet Diabetes & Endocrinology".

 Understanding remains limited of why some obese people appear to be protected from the health risks usually associated with excess fat, such as cardiovascular disease or type 2 diabetes, , and no universally accepted criteria have been developed for identifying metabolically healthy obesity.  The authors of this new paper outline some of the possible factors which might be used to identify the condition – including waist circumference, insulin resistance, and physical fitness – although they point out that considerably more research will be needed if the concept is to become clinically useful.
A clearer definition of the condition of metabolically healthy obesity, and better understanding of the responsible mechanisms would not only mean that costly weight loss interventions such as bariatric surgery could possibly be targeted to the most at-risk obese people, but could also potentially aid the development of drugs that protect against metabolic diseases (diabetes and high blood pressure) which lead to higher illness and mortality among obese people.  A small number of animal studies have suggested that certain proteins produced in the body may protect against the harmful effects of obesity, although further research is needed to establish whether these mechanisms are effective in humans.
According to lead authors Professor Matthias Schulze, of the German Institute of Human Nutrition in Nuthetal, and Professor Norbert Stefan, of the University of Tübingen, Germany, “The health consequences of obesity are well documented. In particular, the worldwide increase in the incidence of type 2 diabetes, cardiovascular disease, and several types of cancer is thought to be largely attributed to the obesity epidemic. Therefore, prevention and treatment of obesity to reduce risk of chronic diseases at the population and individual level is crucial.”
“In view of the magnitude of the obesity epidemic, stratification of obese individuals, in terms of their risk for obesity-related metabolic diseases, becomes more important for prevention and treatment purposes. Potentially, scarce resources can be more effectively used if tailored towards the metabolic profile of an obese individual; some prevention and treatment strategies can be very expensive and time consuming.” 
“At the moment, the public health relevance of metabolically healthy obesity is unclear, because of uncertainties about its definition and clinical applications.  However, developing standard criteria to define metabolically healthy obesity, and gaining a deeper understanding of the biological mechanisms behind it, would potentially remove these barriers, and could lead to improved targeting of treatment. However, this doesn’t rule out the possibility that reasons other than metabolic risk might drive treatment decision for obese persons, and nor does it question that prevention of obesity should be widely promoted”