According to research published in Diabetes Care, terms like "metabolically healthy obese" do not exactly say who is at risk of certain diseases, leading to wrong assumptions about who needs monitoring for conditions such as type 2 diabetes.

Definitions based on how heavy an individual is may be less helpful than what everyone may have thought in predicting not only type 2 diabetes, but also heart disease, high fasting blood sugar or triglyceride levels and high blood pressure, which have been associated with obesity. While these conditions are usually diagnosed at the same time, not every individual who suffer from obesity have these metabolic risk factors, on the contrary,  those people with low body mass index (BMI) do have them.

Medical News Today reported that the idea of the term "metabolically healthy obesity" has been accepted in recent years. The opposite is known as the "metabolically unhealthy lean." A combined study is underway by experts at the Epidemiology Unit of Medical Research Council (MRC) at the University of Cambridge in the United Kingdom, together with their colleagues from the European Federation of Pharmaceutical Industries and Associations to investigate on the validity of the definitions.

Researchers studied data associated with people from 14 different related studies determining the risk of developing type 2 diabetes in lean, overweight and obese individuals. The participants of the study were categorized as metabolically healthy and metabolically unhealthy.

Testing metabolic health with under the lean category, they found that it was not sensitive, but was specific. With obese individuals, sensitivity was fair, but specificity was low. This may indicate that the simplest definitions of obesity and metabolic health that is used at the moment have limited value in a clinical setting.  In other words, while metabolically healthy obese people are at lower risk of type-2 diabetes than those who are metabolically unhealthy obese, they still have a very high risk of developing the disease than people who are lean but "metabolically unhealthy."