Obesity: Definition and epidemiology

In the recent years, obesity has received considerable attention as a major health risk, to the point that some scientists have predicted that it could become responsible for reversing the current trend of increasing life expectancy [ 1 ]. Indeed, obesity is the most prevalent form of malnutrition in the industrialized countries, and it is rapidly becoming highly prevalent also in the developing world. It is considered a multifactorial condition, caused by a complex interaction between the environment, genetic predisposition, and human behavior. The relevance of obesity as a risk factor for medical conditions is very well appreciated; it is now considered as a major contributor to the global burden of disease and disability, because it is linked to various disabling conditions, such as heart disease, diabetes, hypertension, stroke, certain cancers, osteoarthritis, and respiratory abnormalities, and to several digestive diseases, including gastroesophageal refl ux disease (GERD) and its complications, colorectal polyps and cancer, and liver disease (e.g., nonalcoholic fatty liver disease, cirrhosis, and hepatocellular carcinoma) [ 2 ]. Moreover, it has been reported that obesity is associated with an increased risk of death, although the relation of BMI categories with mortality has been the subject of much controversy, because epidemiologic studies have found linear, U-shaped, or J-shaped relationship between BMI and total mortality