The body mass index is used as a guide to establish whether an individual’s weight is within a healthy range or if they are at risk from certain medical conditions due to being over or under weight.
As no two bodies are the same, the index takes into account an individuals’ height and weight and calculates a number specific to them. This number will then give the individual guide as to whether their weight is within a healthy range.
Calculating Body Mass Index
To calculate his body mass index, an individual should divide his weight (in kilograms) by the square of his height (in metres).
- Weight (kg) / (height x height) (m) = BMI
The resulting number will then relate to a score which is graded according to potential health risks.
BMI Scores in Relation to Healthy Weight Ranges
An individual with a BMI score of between 18.5 and 25 is considered to be within the healthy weight range. Although it is generally regarded that a score of 18.5 or less indicates that an individual is under weight, some believe that individuals enter this group if their BMI drops below 20.
At the other end of the scale an individual scoring between 25 and 30 is considered to be in the overweight bracket. This moves into the obese category for those scoring between 30 and 35 and anyone scoring above 35 falls within the very obese grouping.
Risks Associated With Body Mass Index Results
People within the healthy weight range have the smallest risk of developing diseases relating to obesity, this risk increases to a moderate one for those in the overweight range and is much greater for those in the obese and very obese categories. Obesity related diseases include heart disease, high blood pressure (hypertension) and diabetes.
Those with low BMI’s have a greater risk of developing respiratory disease and metabolic complications than those in the 18.5-25 weight range.
BMI Scores May be Misleading for Some Individuals
The index was created to represent average individuals therefore it will give confusing results for certain groups of people. Athletes often produce extremely high readings. This is because the index takes into account the overall weight of an individual and doesn’t separate the individual elements (muscle, fat, bone, water etc.) A very lean athlete may be classified as obese due to their high percentage of muscle mass.
Pregnant and breastfeeding women are also prone to incorrect classification as a result of their body mass index scores. Healthy women in this group need higher fat reserves than normal therefore they should use other methods to determine the risks.
Finally, extra care should be taken when working with a child’s BMI score. Children’s bodies differ greatly to adults’ bodies and special charts have been created to help with this.
The body mass index is a guide only, anyone suffering from health problems should seek medical advice from their doctor.
Sources:
Food.gov.uk, "BMI calculator" (accessed January 25, 2010).
Cancerresearchuk.org, "Body Mass Index" (acessed January 25, 2010).
Weightlossresources.co.uk, "BMI Calculator" (accessed January 25, 2010).
