Obesity is excess weight resulting from a large accumulation of fat in the body that can be detrimental to health. Except for very muscular people; a body weight 20% greater than that established in the standard height and weight tables is arbitrarily considered obese. The root cause of obesity is an imbalance between calorie intake and calorie expenditure. When more calories (food energy) enter the body than are needed to keep it going, the excess is stored as fat. Small amounts that accumulate over a period of time form fat deposits.

Changes in the lifestyle of the civilized world such as increased intake, especially of low-calorie foods, rich in fat and sugar, but low in vitamins and minerals; and decreased physical activity due to the increasingly sedentary nature of many jobs, changes in transportation modes, and increasing urbanization are largely responsible for the increased incidence of obesity.

Various factors also influence obesity, in addition to those already mentioned, such as genetic factors, or environmental and psychological factors. Some people seem to have an inherited tendency to be overweight. It is difficult to determine if it is a genetic or environmental trait. Excess fat causes serious health problems, there are risks of chronic diseases such as diabetes, gallbladder disease, cardiovascular disorders, hypertension, blood clots, some forms of cancer, arthritis, atherosclerosis, shortness of breath and perhaps sterility and sexual problems.

The most common treatment is to reduce the intake of sugar and calories from fat, switch from saturated to unsaturated fats, increase consumption of fruits, vegetables and other nutrients, and increase physical activity. There are other treatments such as the application of drugs that suppress appetite (commonly a mixture of amphetamines), but those who consume them run the risk of becoming drug addicts. There are also surgical techniques such as intestinal bypass and gastric bypass, these sometimes bring certain complications.