How Obesity is Defined?

Maintaining a normal body weight has become a concern in developed countries societies since obesity is associated with various diseases, aesthetic and psychological aspects. Our body weight is regulated by various interrelated complex mechanisms that are controlled by food intake and energy expenditure. In our ancestors, fatty deposits were essential to ensure their survival, since the human body had great energy needs due to intense physical exertion and excessive caloric expenditure due to poor thermal insulation. It should be added that access to food was not insured because it was variable in time and difficult to obtain. In such circumstances, the heat balance tended to be negative so obesity was indicated a positive and desirable attribute. However, in the current welfare society circumstances have changed radically. Excess fatty deposits are widespread in much of the Western population, pose a very serious threat to health. Morbid obesity has become a problem with serious metabolic, mechanical and aesthetic effects, and appears associated with other serious illnesses, to increased mortality.


Obesity is a chronic disease that has a multi-factorial origin, in whose genetic and environmental determinants are involved. It is manifested by an alteration in body composition, causing an increase in body fat. In most cases, the increase in adipose tissue deposits is accompanied by an increase in body weight, leading to a considerable increase in the risk of comorbidity that affects the quality and life expectancy.


Although there are different methods for assessing body fat in our body, in clinical practice and epidemiological research, anthropometry is the most commonly used method. When making a diagnosis and classification of obesity, the World Health Organization (WHO), the International Obesity Taskforce (IOTF) and scientific societies, advise the use of anthropometric data such as weight, height and body circumference. Among the anthropometric measurements, the most widely used indicator in most of the population for assessing adiposity is the ratio of weight in kilograms and height in meter squared, known as Body Mass Index (BMI) or Quetelet index .

BMI = weight in kg / height in meter squared

This indicator is recommended by various scientific societies and international health-related organizations for use in general adult population as the best indicator of body fat, although athletes and the elderly are not considered.
Taking the BMI, is considered obese when BMI value is above 30 kg / m2. The WHO has proposed a classification of body weight and the degree of obesity as follows:

BMI < 18.5 = Underweight
BMI in 18.5-24.9 = Normal weight
BMI in 25-29.9 = Overweight
BMI in 30-34.9 = Obesity grade I
BMI in 35-39.9 = Obesity grade II
BMI >= 40 = Obesity grade III or morbid or extreme obesity.