Viewpoint Sheds Light on Metabolically Healthy Obesity

Marlene Busko

September 02, 2013

The concept of "metabolically healthy obesity"—that is, individuals with a body mass index (BMI) above 30 who do not have metabolic-syndrome factors that put them at risk for cardiovascular disease events—is not new, but is only now being more widely recognized by clinicians, say experts.

As obesity increases globally, it would be useful to be able to identify this subgroup of obese patients, not least to be able to better tailor treatments toward an individual's metabolic profile, the authors of a Personal View published online August 30 in Lancet Diabetes & Endocrinology suggest.

Part of the problem is that there are currently no universally accepted criteria for how to define metabolically healthy obesity, senior author Matthias B. Schulze, PhD, from the Institute of Human Nutrition Potsdam-Rehbruecke, in Nuthetal, Germany, told Medscape Medical News. And the biological mechanisms responsible for this phenotype are largely unknown, making application of the concept difficult in clinical practice.

Nevertheless, the growing recognition of "metabolically healthy obesity" indicates, at the very least, that parameters other than BMI should be considered when physicians are deciding on a clinical approach, they note. Identifying this subgroup of patients could, for example, help pinpoint those who should stick with intensified lifestyle modification as opposed to those who would be more likely to benefit from costly bariatric surgery, he and his colleagues say.

Waist Circumference, Insulin Resistance Predict Risk, Not BMI

Metabolically healthy obese individuals have smaller waist circumference (pear vs apple shape), high insulin resistance, and are "fat and fit," but there are no standardized cutoff points to identify metabolically healthy vs unhealthy obese individuals.

In a literature search, Dr. Schulze and colleagues identified a number of clinical studies, 6 that looked at insulin resistance and 5 that examined cardiorespiratory fitness, "to see whether there are obese [individuals] who could just stay obese and [not] worry about their mortality risk or cardiovascular risk because they are not at increased risk," he explained.

The results were mixed, largely due to the absence of any standard definition for metabolic health, reinforcing the need for the establishment of a consensus on this.

"Some [studies] do see no increased risk [for mortality in individuals with metabolically healthy obesity] at all compared with normal-weight, healthy people, but others suggest it intermediate risk or that the risk is similar to [that of] obese people who have other [metabolic syndrome] risk factors" such as hypertension or high lipid or glucose values.

What is clear "from many studies is that BMI alone is just not sufficient to quantify risk for metabolic disease or for mortality," Dr. Schulze noted. Rather than BMI measurement, waist circumference would be more informative, especially in normal or moderately obese individuals, he noted.

Randomized Controlled Intervention Trials, Cost Analyses, Needed

Laboratory studies have already provided some information about metabolic pathways in metabolically healthy obese animals that could potentially be targeted by new drugs, the researchers note.

And MRI studies in humans have found the same type of fat distribution as has been seen in animal studies: metabolically healthy obese individuals have more subcutaneous fat, less visceral fat, and less fat in the liver and skeletal muscle.

But much more work is required—for example, randomized controlled intervention trials of lifestyle and drug interventions in patients with metabolically healthy vs metabolically unhealthy obesity and cost/benefit analyses for the targeted treatment of obesity on the basis of the metabolically healthy stratification, together with work to assess differences between obese men and women of different ages and races.

And it is important not to lose sight of the importance of trying to prevent obesity in the first place. The authors conclude that "only [focusing] on treatment of cardiovascular risk factors among at-risk individuals is probably insufficient, and prevention of obesity through healthy diet and physical activity should be widely promoted."

The authors have reported no relevant financial relationships.

Lancet Diabetes Endocrinol. Published online August 30, 2013. Abstract


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