Obesity is defined as a situation in which there is excess weight due to abnormal or excessive accumulation of body fat. This disease is considered by the World Health Organization as the second leading cause of preventable death, after the consumption of tobacco. It is a chronic, progressive, and costly sickness, which is associated with many disorders or diseases (co-morbidities), which are aggravated by the severity of obesity and improve, almost always, when obesity is treated properly. The incidence of obesity was dramatically doubled in the last decade. More than a third of the world's adult population has some degree of overweightness or obesity .

Obesity in children and adolescents is also increasing steadily. The most practical way to determine the degree of obesity of an individual, is to calculate the Body Mass Index, ie, the relationship between weight and height squared (BMI = kg/m2). Thus we can have each person have different degrees of severity of obesity as BMI (kg/m2).

Morbid Obesity (or serious) is when you reach the point where it significantly increases the risk of or to already have a disease (co-morbidity) caused by excess weight, causing many times disability and even death. In general, morbid obesity is a condition where excess weight is greater than 30 kg and a BMI greater than 35kg/m2. It is a chronic disease, so the symptoms accumulate gradually over a period of time.

The term Bariatric Surgery comes from the Greek word "baros" meaning weight and "iatrein" treatment. This surgery is not "Endocrine Surgery", because the endocrine glands (eg thyroid, parathyroid, pancreas, and adrenal glands) are not sick, nor are they operated on. Nor, should it be considered as an "aesthetic or cosmetic surgery," for the purpose of this surgery is to lose weight to neither avoid the complications of obesity and not dry fat or skin nor suck the fat. The aesthetic benefits are important and are obtained as secondary to the bariatric procedure over time.

Obesity carries risks, and shortens life expectancy. In people whose weight exceeds twice their ideal body weight, the risk of premature death is doubled in relation to non-obese people. The risk of death from diabetes or heart attack is 5 to 7 times higher. Some of the diseases or co-morbidities frequently associated with morbid obesity include hypertension and heart disease because the excess body weight reduces the ability of the proper functioning of the heart. Hypertension (high blood pressure) can lead to strokes, heart attacks and kidney failure.