Being aware of your body mass index score can be a useful guide to keeping a healthy weight, but it’s not the whole story, especially for children.

There is a really great online tool on the NHS Choices website which allows you to enter you and your family members’ height, sex, age and weight and instantly get your BMI score, with advice on what those results mean. However, whilst this is a useful way of taking a step back from simply weighing yourself, and instead looking at your stature and other physical factors, there are other measures that are important to consider, too.

What is BMI?
Your BMI is the measure of your weight relative to your height to assess your risk of developing diseases linked to being overweight. BMI scores signal the following:
• Less than 18.5 – underweight
• 18.5 to 24.9 – normal
• 25 to 29.9 – overweight
• 30-plus – obese

The BMI score is a crude population assessment tool for body assessment. It gives an approximation of possible total body fatness and does not take into account more athletic bodies with a muscular build. In these cases it overestimates body fat in very fit adults. Also, in older people who have lost muscle mass, the body fat may be underestimated. Ethnicity is also not taken into account when using BMI scores, and this can affect the risk level of developing certain conditions.

Other ways to gauge body health

• Waist measurement.
Fat around your middle is another useful indicator of the risk of developing diseases linked to obesity. Put a tape measure round your waist, not squeezing too tight. For men, a waist measurement of over 40 inches (101.6 cm) and for women, a waist measurement of over 35 inches (90cm) will signal an increased risk of obesity-related disease.

• Family health and ongoing conditions.
If you or a close blood relative has problems with high blood pressure, cholesterol, heart disease and certain other known medical issues, then these also need to be taken into account along with your body measurements.

• Lifestyle.
Habits like smoking and a lack of physical exercise can also increase the risk of problems like heart disease no matter what shape and weight you are.

BMI and children
In children, don’t use the above criteria, developmental stage is very important in children and the BMI scores mean different things for children. The child BMI score takes into account age and sex, compared against average measurements for other children their age. Therefore the BMI score is simply a comparison based on average childhood measurements and these are currently based on averages in a British study from 1990. Puberty can also affect how the BMI score should be regarded. However, if your child (of any age) has trouble fitting clothes intended for his or her age, and does not seem to cope well with physical activity, getting breathless or being simply unwilling to do any exercise, then speak to your GP.

What next?
If your BMI score and those of other members of your family, are normal, then great. However, do remember that lifestyle affects your health outlook as well as shape and size! If you are concerned and don’t know how to approach what you have found, speak to your GP or the nurse at your local surgery as they should be able to get you and your family on a healthier path. Check out the Live Well pages on the NHS website for ideas on how to improve your family’s habits.