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Unit 4 > Unit 4 > Body Mass Index – BMI

Body Mass Index – BMI          

BMI (Body Mass Index) is a physical measurement of an individual’s body fat based on their height and weight.  It is applicable to both men and women between the ages of 18 and 65 years.  It can be deceiving when used with younger individual’s as all individuals develop at different rates, so, it needs to be used with caution with any individual under the age of 18 years.  Also, body frames vary and it is difficult to work out an individual’s body frame, some have small frames and some have large frames.  This will effect an individual’s weight.  Therefore, it is more accurate to recommend a weight range rather than an exact weight for a given height.  This is the reason why the Body Mass Index is recommended and height weight charts are not.  

BMI is one of the physical measures used to  assess an individual’s weight.  It is one method to indicate if an individual is overweight, obese, underweight or normal.  If an individual has concerns about their weight they should see their GP who will be able to assess an individual’s specific situation. The BMI physical measurement is not accurate for individual’s who are muscular as muscle weighs four times more than fat and this would push them into a higher category even if they have a healthy level of body fat.  It is not accurate physical measurement for individual’s who are frail or women who are pregnant or  breastfeeding.  

Safety

  • The individual must give their consent for their BMI  to be measured
  • Reassure the individual that the result is confidential
  • Make sure the individual is not embarrassed, they may prefer to take their own measurements i.e. weigh themselves.
  • If measuring an individual’s BMI is likely to affect them emotionally or psychologically then use a different physical measure for the controlled assessment.
  • It can be deceiving when used with younger individual’s as all individuals develop at different rates, so, it needs to be used with caution with any individual under the age of 18 years.
  • If an individual is in the underweight or obese BMI category advise them to see their GP to discuss any lifestyle changes.

To calculate an individual’s BMI follow these three steps:

  1. Work out their height in metres and multiply it by itself(height squared).
  2. Measure their weight in kilograms
  3. Divide the weight by the height squared (ie. the answer to step1).

Height2=  Height in metres x height in metres         weight                      weight in kilograms               

For example, they might be 1.6m (5ft 3in) tall and weigh 65kg (10st 3lb).

The calculation would then be:

1.6m x 1.6m = 2.56. BMI would be 65kg divided by 2.56 = 25.39 BMI

1.62    =   1.6m x 1.6m   =    2.56  = 25.39 BMI             65kg              65kg                65kg

To check your answer use the BMI calculator found on the following website:

http://www.bbc.co.uk/health/tools/bmi_calculator/bmi.shtml

Conversions from imperial measurements to metric measurements

To convert  an individual’s height from feet and inches into centimetres  follow these steps:

  • Convert the  height into inches
  • Multiply this number  by 0.0254 this will give the height in metres m

For example:  Height 5 foot 3 inches          

  • Convert the  height into inches            5 x 12 = 60 + 3 =   63 inches
  • Multiply this number  by 0.0254 this will give the height in metres m     

         63 x 0.0254 = 1.6m

To convert  an individual’s weight from pounds  into kilograms  follow these steps:

  • Convert the  weight into pounds
  • Multiply this number  by 0.4536 this will give the weight in kilograms kg

For example:  weight 10stones and 3 pounds         

  • Convert the  weight into pounds             10 x 14 = 140 + 3 =   143 pounds
  • Multiply this number  by 0.4536 this will give the weight in kilograms   

         143 x0.4536  = 65kg

BMI chart

Underweight BMI less than < 18.5
Ideal BMI 18.5 – 24.9
Overweight BMI 25 – 29.9
Obese BMI 30 – 39.9
Very obese BMI greater than > 40

BMI Results

If an individual’s BMI is:

Less than 18.5 they are classified as underweight.  It may mean their weight is too low.  They should consult their GP to find out if they should gain weight.  A low body mass will reduce the body’s immune system which can lead to illness.  The best way to gain weight is to eat more carbohydrate.

Between 18.5 and 24.9 they are classified as normal or ideal weight.  They need to be encouraged to maintain this weight.  The statistics say these individuals will live the longest and have less illness.

Between 25 and 29.9 they are classified as overweight.  These individuals need to find a healthy way of reducing their weight by altering their diet and increasing the amount of exercise they take part in.  They need to balance the number of calories they intake with the number of calories they use each day.  To lose weight they need to consume less that they use.  They have an increased risk of being ill.

Over 30 they are classified as Obese.  These individuals are in an unhealthy condition which increases their risk of serious illnesses, such as heart disease, diabetes, high blood pressure, gall bladder disease and some cancers.  They need to alter their lifestyle by improving their diet and increasing the amount of exercise they take part in.