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Welcome to the Health Defence Blog - a blog about health, wellness and a healthier you. Brought to you by the Health Defence team at Chest Heart & Stroke Scotland, you'll find up-to-date information on a range of topics from what's in your food to the latest advice on e-cigarettes!


Megan - Health Promotion Specialist

June 19, 2016

No, it’s not a spelling mistake – this week’s Live Better Blog looks at different measurements for determining obesity – BMI and Waist Circumference. Both have their pro’s and con’s, but which, if either, is best?

BMI or ‘Body Mass Index’

BMI is one way that adults can measure how healthy their weight is for their height using the following equation:

BMI = Weight (kg)/Height (m)2

The higher your BMI the higher your risk of developing obesity-related health conditions. BMI is a useful indicator for how much body fat we carry.

  • The BMI scale – where do you fit? (hint: scroll down for an easy-to-use BMI calculator)

BMI levels

  • Why is BMI useful?

BMI is a quick way of determining whether someone is considered to be underweight, healthy weight, overweight or obese. Being overweight or obese increases your risk of health problems, ranging from joint pain right through to heart disease, diabetes and high blood pressure.

  • When is BMI less useful?

BMI isn’t perfect.  This is because it can't distinguish between fat and muscle mass. Muscle weighs more than fat, so if someone is very muscly, their BMI might be overestimated. For example, rugby players often have BMI’s in the obese range (i.e. more than 30) but physically appear to be ‘healthy’.

As well as athletes, there are some other groups of people who BMI might also not be useful for:

  • Pregnant women: increased weight during pregnancy means that BMI is inaccurate. However, women should aim to have a healthy BMI before getting pregnant.
  • Some ethnic groups (such as Black, South Asian or Chinese), may have a higher risk of diabetes and heart disease at a lower BMI.
  • Elderly people: we lose muscle mass and gain fat as we age, making BMI less reliable.

 Waist Circumference

Waist circumference tells us a lot about where we carry our weight (or fat mass). A larger waist circumference puts you at higher risk of developing heart disease, diabetes and stroke. This is because of where that fat is being carried – right around your organs, which is the most dangerous place.

skeleton WC

Image courtesy of the National Heart, Lung and Blood Institute*

  • How to measure your waist circumference:

Find the bottom point of your ribs and the top point of your hip, and measure around your middle at a point mid-way between these (hint: this is usually around your belly button).

Tip: no sucking your tummy in! For an accurate measurement, breathe out naturally first.


  • Waist circumference guide:

The chart below will give you an indication of how your waist size affects your risk of heart disease and other health conditions:

waist guidelines

  • Why is waist circumference useful?

While BMI is a good way to tell if you are a healthy weight, your shape can also affect your health risk. Fat around your middle can increase your risk of getting heart disease or developing other long-term health problems. Even if your BMI is normal, you should aim to have a waist circumference within the ‘ideal’ range, and lose weight to achieve this if necessary.

Waist circumference can also be a good way to measure weight loss!  You will see a reduction in waist size if you are losing fat.

  • When is waist circumference less useful?

There are also times when waist circumference isn’t a good measurement, such as in pregnancy or if your tummy is distended due to a medical condition.

Similarly to BMI, it may be beneficial for some ethnic groups to aim for a slightly lower waist circumference to reduce their risk of cardiovascular disease. You can discuss this further with your GP or practice nurse.

Hint: don't measure your waist circumference more than once a month. 

Remember, you can also monitor your weight and waist size by how well your clothes fit! 

Should you still use BMI as a measure of wellness?

Yes, but as a guide and in conjunction with other measurements such as waist circumference. Health professionals often use a combination of BMI and waist circumference measurements to assess weight and associated disease-risk.

Still unsure: give our Advice Line Nurses a call on Freephone 0808 801 0899 or check out our guide to ‘Losing Weight’..


*Image credit: Guidelines on Overweight and Obesity: According to waist circumference.

***Disclaimer: always seek medical advice before starting a new diet, exercise regime or medication. The information in these articles is not a substitute for professional advice from a GP, registered dietitian or other health practitioner.

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