Well the simple answer would be to say that being obese is nothing more than being very overweight. In other words, it's simply a matter of degree. Unfortunately, this answer misses the central issue of obesity.
Putting on a few pounds won't do you any real harm and, apart from the fact that your pants may feel a little tight and you may be less than happy with the way you look, there are even some people who believe that carrying a little extra weight might actually be good for you. Indeed, there are some studies that show that death rates are slightly lower amongst individuals who are slightly overweight, although there is considerable debate about whether or not this is actually related to weight or results from other factors which are more often seen in people who are overweight.
Once your weight passes a certain level though, so that you are now carrying sufficient extra weight to be classed as being obese, the scales tip and you begin to run the risk of developing a series of health problems as a result of your excess weight. Indeed, if your weight continues to climb, these health problems can literally become life-threatening and your obesity will then be classed as morbid obesity.
This is all very well, but how do you know whether you're simply overweight or obese?
The main measure of obesity was developed by a Belgian statistician and anthropometrist named Adolphe Quetelet nearly one hundred and fifty years ago and is referred to as the measurement of body mass index, or BMI. In simple terms your BMI is calculated by dividing your weight in kilograms by the square of your height in metres. So, if you are 1.7 metres tall and weigh 70 kilograms your BMI would be 24.2 [70 รท (1.7x1.7)].
A BMI of between 18.5 and 24.9 is considered to be normal. Between 25.0 and 29.9 you would be classed as being overweight. Once you reach a BMI of 30 you are considered to be obese and, if your BMI reaches or exceeds 40 you are morbidly obese.
BMI is designed as a general guide but there are circumstances in which it is possible to have a BMI of less than 30 and still be clinically obese and indeed to have a BMI of more than 30 and not to be classed as being obese. A lean but muscular individual could, for example, have a BMI of over 30 but, in this case, the excess weight would be provided by muscle rather than by fat.
As a result, where your weigh becomes a concern and obesity a possible issue, further more accurate tests should be carried out by your doctor to determine whether or not your are clinically obese.
