The New BMI

The Old BMI

It is now known that the BMI represents a rapid but INDICATIVE indicator for assessing the body weight of a subject in relation to an ideal weight, called "ideal weight". Also known as the Quetelet index, from the name of the Belgian scientist Adolphe Quetelet who developed it as far back as 1830, the BMI stands for Body Mass Index, Italianized in "Body Mass Index" (IMC is synonymous with BMI)

The BMI is obtained by dividing the weight (in kilograms) by the height (in meters) to the square of the subject in question. For example, if a subject weighs 80 kg and is 175 cm tall, his BMI is equal to ::
80 / (1.75x1.75) = 26.12 Kg / m2

BMI	CONDITION
<16.5	SERIOUS MAGREE
16 to 18.49	UNDERWEIGHT
18.5-24, 99	normal weight
25 to 29.99	OVERWEIGHT
30 to 34.99	CLASS I OBESITY (mild)
35 to 39.99	CLASS II OBESITY (average)
> 40	OBESITYCLASSES III (serious)

The result of the formula is then compared with the averages of the reference population, in order to classify and evaluate the weight of the subject. The best known table is that of the World Health Organization (table on the side).

The subject of our example (BMI = 26.12), therefore, appears to be slightly overweight.

Limits of the Old BMI

As anticipated, the BMI is a practical and reliable index to assess the body weight of the GENERAL population. However, this parameter loses reliability in the following cases:

MUSCULOSIS / ROBUST INDIVIDUALS - Particularly developed bone and muscle mass (OVERLOOKING THE BODY WEIGHT EVALUATION: the subject, for example, is classified as overweight although it has a normal or even lower than normal fat mass)
EXILE INDIVIDUAL - Particularly reduced bone and muscle mass (UNDER THE EVALUATION OF THE BODY WEIGHT: the subject, for example, is classified as normal weight although it has an excessive fat mass)
Very high stature (OVERLOOKING THE BODY WEIGHT EVALUATION: the subject, for example, is classified as overweight although it has a normal or even lower than normal fat mass)
Very low stature (UNDERLYING THE EVALUATION OF THE BODY WEIGHT: the subject, for example, is classified as normal weight although it has an excessive fat mass)

The new BMI

Researchers at Oxford University have studied a new mathematical formula to overcome SOME limits of BMI, by more accurately evaluating the amount of actual fat even in VERY HIGH or VERY LOW individuals. Unfortunately the new calculation is more complex than the previous one and requires a scientific calculator:

NEW BMI: 1.3 x weight (Kg) / (Height (m)) 2.5

Referring to the previous example (subject 80 kg high 175 cm):

1.3 x 80 / (1.75) 2.5 = 104 / 4.0151 = 25.67 Kg / m2.5

The difference of the result with that of the old BMI is rather thin, but it becomes important for individuals who measure less than one meter and 52 centimeters and for those more than two meters tall.

Even the new BMI remains inaccurate in assessing the body weight of very robust and muscular or very thin individuals (with reduced bone mass and hypotrophic musculature).