When Being Lean Is Not Enough: The Metabolically Unhealthy Normal Weight Phenotype and Cardiometabolic Disease

Conventional wisdom associates increased body weight with suboptimal health.However, it has become apparent in recent years that excess weight and total body fat do not necessarily impair metabolic function and increase the risk of cardiometabolic disease.Vice versa, the absence of excess body weight and fat does not necessarily reflect better health and a low disease risk.Individuals with obesity typically present with hypertension or metabolic abnormalities such as hyperglycemia, hyperinsulinemia, and dyslipidemia.These risk factors are also present in a subset of people with normal body weight ("metabolically unhealthy normal weight" or MUNW), particularly among Asian populations.Compared with control subjects with the same body mass index and total body fat, MUNW individuals have dysregulated glucose homeostasis (insulin resistance and hyperinsulinemia) and greater accumulation of fat in the upper body (intraabdominal region and liver) than in the lower body (legs).Mild diet-induced weight loss in MUNW individuals improves body composition and metabolic function in a manner that is qualitatively and quantitatively similar to that in people with obesity.However, weight loss cannot be a long-term treatment solution for this phenotype; therefore, alternative therapies need to be developed together with screening programs for early identification.