My thought is that maybe Metabolic Flexibility will be a way to differentiate between the groups? For some more info on that, see this post on Metabolic Inflexibility.
"Identification and Characterization of Metabolically Benign Obesity in Humans"
Norbert Stefan, MD; Konstantinos Kantartzis, MD; Jürgen Machann, PhD; Fritz Schick, PhD; Claus Thamer, MD; Kilian Rittig, MD; Bernd Balletshofer, MD; Fausto Machicao, PhD; Andreas Fritsche, MD; Hans-Ulrich Häring, MD
Arch Intern Med. 2008;168(15):1609-1616.
Background Obesity represents a risk factor for insulin resistance, type 2 diabetes mellitus, and atherosclerosis. In addition, for any given amount of total body fat, an excess of visceral fat or fat accumulation in the liver and skeletal muscle augments the risk. Conversely, even in obesity, a metabolically benign fat distribution phenotype may exist.
Methods In 314 subjects, we measured total body, visceral, and subcutaneous fat with magnetic resonance (MR) tomography and fat in the liver and skeletal muscle with proton MR spectroscopy. Insulin sensitivity was estimated from oral glucose tolerance test results. Subjects were divided into 4 groups: normal weight (body mass index [BMI] [calculated as weight in kilograms divided by height in meters squared], <25.0), style="font-weight: bold;">Conclusions: A metabolically benign obesity that is not accompanied by insulin resistance and early atherosclerosis exists in humans. Furthermore, ectopic fat in the liver may be more important than visceral fat in the determination of such a beneficial phenotype in obesity.