There is what is called the Body Mass Index (BMI), which is a measure of body fat, calculated using a formula that requires the height and the weight of an adult (either man or woman). Persons with a BMI of less than 18.5 are underweight. A person is considered to be of normal weight if his or her BMI is between 18.5 and 24.9; overweight if the BMI is between 25 and 29.9; and obese if it is 30 and above. If the BMI is 40 or exceeds 40, then the person is said to be morbidly obese. Morbid obesity is also described as a 'clinically severe obesity', that requires urgent medical intervention.

The BMI figures given above are compiled and supplied by the National Heart, Lung and Blood Institute (NHLBI). One problem with the BMI is that it does not give the right estimate of the body fat in cases of persons with a muscular build (as in the case of athletes) or those who have lost their muscle mass (as in the case of old people). Usually, however, the BMI is a fair indicator of obesity.

When you have accumulated excessive fat in the body tissues, you have obesity, a condition that may increase the risk to several health conditions such as diabetes, ailments of the heart, stroke or paralysis and so on. Excess weight is always a health risk. Millions of people (more than a third of the adults) suffer from obesity and the attendant health problems. Included among them are those with morbid obesity. It is estimated that almost 5 to 10 percent of the obesity-affected population is in need of immediate medical care and treatment, because of morbid obesity.

That over-eating causes overweight or obesity may not be news. Nevertheless, there may also be some other factors responsible for obesity. A large number of scientific studies link obesity to genetic factors. Scientists from the National Institutes of Health have been studying the occurrence of obesity in the Pima Indians of Arizona and Mexico for decades, because they are among the most obese people in the entire world, some of them weighing more than 500 pounds. That amounts to very severe obesity. No wonder, most of them, especially the Pima tribes in Arizona, are found to have diabetes and heart problems. Certain people therefore are genetically predisposed to obesity. Processed or fast food and a sedentary lifestyle, with little or no time devoted to physical activity or exercise and with no need or even desire to walk (the advent of the car being the culprit here) are found to contribute to obesity. In addition, some medical conditions like hypothyroidism and steroid-intake result in obesity.

Excessive weight, which is usually visible in a person's girth, or the circumference of the person's waist, due to the accumulation of too much fat in the abdomen, leads to serious health risks, including death in severe cases of obesity, especially morbid obesity. Therefore, irrespective of the causes of obesity, it is essential for obese people to take suitable steps for losing as much weight as is necessary to bring it to the level of normal BMI.