The International Classification of Diseases first recorded obesity in 1948. The misconception that obesity is merely a lifestyle decision that can be reversible through the exercise of willpower has persisted in public discourse and in the medical community. However, obesity is recognized by the World Health Organization (WHO) as a chronic disease characterized by “an abnormal or excessive accumulation of fat that is a health hazard.” In the context of patient care, there is an important and simple logical inconsistency: the therapeutic field is still based on the Body Mass Index (BMI). This indicator only measures weight and height, without considering body fat, muscle mass, or metabolic status, leading to imprecise diagnoses. The consideration of obesity as a disease based on BMI alone impedes progress in social recognition and understanding of the disease, leading to unintended iatrogenesis and hindering research. Hence, it is indispensable to evaluate body composition and metabolic status, as well as to differentiate between clinical and preclinical obesity, in order to target and treat more equitably. The purpose of this systematic review is to address the latest progress in the ambiguity surrounding the diagnosis of obesity based on BMI, and how it impacts individuals.