|Body Mass Index (BMI) is a number calculated using a person's weight and height. Healthcare professionals worldwide use BMI to see how a person’s weight relates to their height – the calculation can thereby help determine whether a person is underweight or clinically obese, for their height.
The Body Mass Index (BMI) formula was developed by Belgium statistician Adolphe Quetelet (1796-1874), and was known as the Quetelet Index. BMI is also referred to as 'body mass indicator'. BMI is an internationally used measure of obesity.
The metric BMI formula accepts weight measurements in kilograms and height measurements in metres.
BMI is equal to weight in kilograms, divided by your height in metres squared
If a adults’ weight is 60kg and their height 1.68m, then-
BMI=60 / (1.68 x 1.68)
For most adults, an ideal BMI is in the range of 18.5 to 24.9. If your BMI is 25 or more, you’re over the ideal weight for your height:
- 25 to 29.9 is overweight
- 30 to 39.9 is obese
- 40 or more is very obese
If your BMI is less than 18.5, you're under the ideal weight for your height.
If your BMI is 25 or more, and you have been classified as overweight or obese by your healthcare practitioner, then there is an increased risk of health problems, such as:
- Heart disease
- Type 2 diabetes
- Some types of cancer
- High blood pressure (hypertension)
- Kidney disease
If your BMI is less than 18.5, and you have been classified as underweight by your healthcare practitioner, then there is an increased risk of health problems, such as:
- Brittle bones (osteoporosis)
- Absent periods in women (amenorrhoea)
- Iron deficiency (anaemia)
In recent years there has been a sharp increase in the number of clinically obese children. If present trends continue, there are fears that obesity-related diseases (such as diabetes) will occur at a much younger age than at present. Calculate your child's BMI using the same method as for adults - weight in kilograms divided by height in metres squared. However, it is important to remember that adult BMI charts must not be used to determine whether a child is overweight or obese. Specific age-adjusted charts are needed.
Although you can get a general estimate when working out your BMI yourself, it is always better that you get a specialist healthcare professional to do it for you as not all adults who have a BMI in the "Normal" range are healthy.
A person may have lots of fat but very little muscle, so if your BMI is within the normal range, then it may still be considered unhealthy due to the high fat levels.
Similarly, if you are an athlete or exercise a lot, then you may have a lot of muscle, which weighs more and will affect the readings. Your BMI could be higher than the normal range, but it could still be considered as healthy.
You should not use BMI as a measure if you’re pregnant. Get advice from your Gynecologist or GP if you’re concerned about your weight.
Measuring waist circumference in conjunction with the BMI, normally results in a more accurate representation of the general health risk of an individual. Carrying too much fat around your middle is associated with an increased risk of developing heart disease and diabetes. It's also associated with a greater risk of high cholesterol levels which, in turn, increase the risk of heart attacks and strokes.
By losing weight if your BMI has been classified as too high
- By gaining healthy weight if your BMI has been classified as too low
- Eating healthy, regular and balanced meals
- Regular exercise
If you intend to go on a low-fat or low-calorie diet to achieve gradual weight loss or plan to introduce exercising into your daily routine, you should seek advice from a Dietician or Doctor beforehand, especially if you have a long-term health condition, such as type 2 diabetes or history of heart failure.