Obesity is most commonly defined as a BMI of over 30kg/m2. Typical classification is into categories of Class I (BMI >30 kg/m2), Class II (BMI equal to or over 35 kg/m2) and Class III (equal to or over 40 kg/m2), with the latter also known as severe obesity. While this method is most frequently utilized by clinicians, it has limitations-such as in those individuals with high muscle to fat ratios or those of Asian descent. Alternate methods for obesity definition and classification include data such as waist circumference, hip to waist ratio, or body fat percentage.
Using the BMI criteria for obesity, over 600 million people worldwide, including one third of adults in the United States meet criteria for obesity [1]. In the United States, this translates to mounting healthcare costs (estimated close to 128 billion dollars in 2008) and increased mortality compared to normal weight individuals [2]. Cardiovascular disease and secondarily malignancies has long been identified as the primary reason for these increases in mortality and costs. This in turn has been attributed to a worse metabolic profile which includes various combinations of impaired glucose tolerance/type 2 diabetes, dyslipidemia, hypertension and systemic inflammation.
However, hidden amongst traditional obesity related concerns, there lies a subset of patients without the expected sequelae of their weight. These patients circumvented the classic models of metabolic and cardiovascular risk, and are known as the “metabolically healthy obese” (MHO). Simultaneously, there are individuals who despite having “normal” weights, shoulder an increased burden of these risks. Accurate classifications and mechanistic understandings for individuals with these conditions would be required to ensure the best health care and appropriate treatments as well as to decrease health care costs due to improper treatments and requisite subsequent medical interventions. Here we discuss the current knowledge surrounding these two groups, and highlight important features for provider management.
Historically, the primary concern regarding obesity was due to the concurrent metabolic and cardiovascular risk. Yet, in recent years increased notice has been made of those individuals who do not fit into this traditional phenotype. Instead, metabolically healthy obese (MHO) and metabolically unhealthy normal weight (MUHNW) patients are generating important discussions regarding the classification of metabolic, and thus cardiovascular risk in patients. These cohorts have been previously highlighted in Metabolism, with discussions in recent years ranging from the association with diabetes, liver enzymes and vitamin D to the role of weight status and inflammation [3–9]. Here we discuss these two phenotypes, highlight current knowledge regarding their classification, development and management features for healthcare providers.
Presently, beyond cutoffs for surgical intervention, obesity guidelines do not distinguish between management of the various subclasses of obesity despite the fact that there has not been evidence for increased mortality in simple Class II Obesity [10]. In fact, while studies have shown that individuals with Grade II-III have greater mortality, there is evidence that Class I obesity patients may have lower all-cause mortality than normal weight patients [11]. Furthermore, existing guidelines also fail to individualize the management of MHO or metabolically unhealthy/abnormal obese (MUHO/MAO) patients. This is further complicated by a gap in the recognition and appropriate management of those normal weight individuals, who demonstrate high risk metabolic risk profiles
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