Diagnosis - Obesity

Talk to your GP or doctor if you:

• want advice on managing your weight
• feel your weight is having a bad effect on your life or health

Getting a diagnosis of obesity

To diagnose obesity, your doctor may assess your:

• body mass index (BMI)
• waist to height ratio - if your body mass index is less than 35
• weight-related health problems

They may ask about:

• how your weight impacts your life
• health problems related to weight
• changes in your weight over time
• your sleep, diet, and physical activity
• your work and home environment
• stress in your life
• smoking and drinking alcohol
• your family history
• medicines you are taking

Body mass index (BMI)

Checking your body mass index (BMI) is one way to see if you might be at risk of developing long-term conditions such as obesity.

BMI is a measure of your weight in relation to your height. BMI alone does not give you a measure of your health.

To calculate your BMI, divide your weight in kilograms by your height in metres squared.

BMI cannot tell the difference between muscle and fat. For example, if you have a lot of muscle, you may have a high BMI despite having low body fat. In this case, your waist circumference (the distance around your waist) may be a better guide.

Who should not use BMI

BMI is not a suitable measurement to use if you:

• are under 18
• are pregnant
• have an eating disorder, or think you may have one
• have a condition that affects your height

Calculate your BMI

To calculate your BMI:

1. Measure your weight in kilograms.
2. Measure your height in metres.
3. Multiply your height in metres by itself. This is called your height squared.
4. Divide your weight by your height squared.

People with a BMI of 30 or more have a high risk of obesity.

You should also take into account your ethnic background.

You have a higher chance of developing health problems at a lower BMI if your ethnic background is:

• South Asian
• Chinese
• other Asian
• Middle Eastern
• Black African
• African-Caribbean

The NHS have a BMI calculator. It takes into account your ethnic background, as well as your weight and height. It is important to use a BMI calculator that takes these into account.

Your BMI result

Your BMI result is a number in one of these BMI categories:

• underweight
• healthy weight
• overweight
• obesity

These categories do not diagnose weight-related health problems or obesity. They help to show if you may be at risk.

Talk to your doctor about your BMI result if you feel your weight is affecting your health.

Waist to height ratio

Another way to check if you may have excess body fat is your waist to height ratio.

You can use this if you are an adult with a BMI under 35. If you have a BMI more than 35 this measurement is not as accurate.

To measure your waist to height ratio, divide your waist measurement by your height. You need to use the same units for both measurements. For example, both in centimetres or both in inches.

When you measure your waist:

• measure at the middle point between your lowest rib and your hip bone
• breathe naturally - do not hold your breath or hold in your tummy

For example, if your waist is 80cm and you are 160cm tall, you would calculate your result like this: 80 divided by 160. This equals 0.5.

A waist to height ratio of 0.5 or higher means you may have increased health risks.

Talk to your doctor about your waist to height ratio if you feel your weight is affecting your health.

Health problems linked to weight

Your doctor can also check if you have any health conditions linked to your weight.

These conditions can include:

• high blood pressure
• high cholesterol
• raised liver enzymes
• pre-diabetes or type 2 diabetes
• heart disease
• muscle or joint conditions, such as osteoarthritis
• physical limitations, such as shortness of breath and poor mobility
• mental health issues, such as anxiety or depression

They may also ask to do health checks to assess if your weight is affecting your health. These checks could include blood tests and measuring your blood pressure.

This will help your doctor to understand your risk of developing obesity. They will then work with you to decide on a treatment plan that best suits you.

Treating obesity