What is obesity? It is generally considered to begin at a weight relative to height that is 20 to 30% above desirable weight. Desirable weight being the mid-point of weight ranges associated with greatest longevity; data which is extracted from life-insurance statistics.
The Body Mass Indicator (BMI) is the internationally used standard for classifying an individual’s weight-for-height.
You calculate by dividing the person’s weight in kg by their height in metres, squared.
Below is a handy calculator, which works with both metric and imperial measurements
And these are the ranges:
|Normal||18.5 – 24.9|
|Overweight||25 – 29.9|
|Morbidly obese||> 40|
February 2013: Update on BMI calculation
Mary Farmer, IL’s nutrition expert writes…
At last, the mathematical experts have caught up! We have already discussed the pros and cons of the BMI tables, aka “The Quetelet Index” in the Nutrition Blogspot. It is now generally recognised that they may be useful for groups of people but can lead to misleading results and misunderstandings, when used for individuals. A Belgian scientist, Adolphe Quetelet figured the calculations out in the 1830s. However, they have now been challenged by a team from Oxford University, suggesting that the basic formula is flawed, due to the fact that not all dimensions of the human body grow in proportion. And, of course, there were no computers or calculators in the 1830s, nor was there an obesity problem. Which might explain why the BMI tables have been accepted for so long, as they are easy to use: no one wants a complicated formula.
The current BMI, says Nick Trefethen, misleads short people into thinking that that they are thinner than they actually are and tall people into thinking that they are fatter. His suggested new formula (1.3 x weight in kg / height x 2.5 in metres) is a better approximation of reality, as it scales more accurately. Using this, short people would gain a BMI point, while taller people would lose one. Mr Trefethen suggests that, although the truth can be uncomfortable, it is better to have a good science base where health is concerned. He wonders for how long, agencies such as the NHS and obesity researchers may continue to use the flawed formula! (And I still have strong reservations about its use in elderly persons).
Obesity is associated with conditions such as high cholesterol, high blood pressure and diabetes, which increase the risk of coronary heart disease, stroke and kidney disease. Cancer of the uterus, breast cancer and gall bladder disease are also more prevalent amongst obese individuals. Risk of premature death is greatest for people who become obese at an early age, and there is some evidence that greater distribution of excess fat to the upper body is more dangerous than lower body fat.
More information about the consequences of gross obesity can be found here