What is obesity?
For most adults, a body mass index (BMI) of 30 or above is classed as obesity, while a BMI of 40 or above is classed as severe obesity. Obesity develops when excess energy is stored in the body as fat, and it is a complex issue influenced by many factors, including diet, physical activity, genetics, health conditions, and certain medicines.
Why is obesity a problem?
Living with obesity can increase the risk of developing a number of health conditions, including type 2 diabetes, heart disease, stroke, high blood pressure and some types of cancer. It can also affect day-to-day life and mental health, including contributing to low mood or depression.
How is obesity measured?
Body mass index (BMI) is one way healthcare professionals assess whether your weight may be affecting your health. BMI is calculated using your height and weight, although it does not provide a complete picture of your health.
While healthcare professionals find BMI a useful tool for quickly identifying potential health risks, it does not provide a detailed, full picture of your health. Some experts believe that BMI alone can be confusing and an oversimplification.
We explain more about other ways you can track your physical health.
Understanding your BMI
You can use the free NHS BMI healthy weight calculator to check your BMI, as well as to find out more information about what your BMI number means. For most adults:
- under 18.5 is classified as underweight;
- 18.5 to 24.9 is classified as a healthy weight;
- 25 to 29.9 is classified as overweight;
- 30 to 39.9 is classified as obese;
- 40 or above is classified as severely obese.
BMI alone doesn't typically diagnose obesity. This is because you may have a particularly high muscle mass, resulting in a higher BMI without a high percentage of body fat.
Some ethnic groups have lower BMI thresholds because health risks can occur at a lower BMI. The NHS BMI calculator accounts for this.
Waist measurement and health
For adults with a BMI under 35, measuring your waist in relation to your height can help indicate whether you are carrying excess fat around your waist, which can increase your risk of certain health conditions.
NICE recommends keeping your waist measurement to less than half your height. A waist-to-height ratio of 0.5 or above is associated with increased health risks, while a ratio of 0.6 or above is associated with further increased risks.
How can obesity affect your health?
Living with obesity can affect your health and wellbeing. Some people may experience:
- breathlessness
- snoring
- difficulty with physical activity
- feelings of tiredness or lethargy
- joint or back pain.
Obesity can also increase your risk of developing serious health conditions, including:
- type 2 diabetes
- heart disease
- stroke
- high blood pressure
- osteoarthritis
- fatty liver disease
- some cancers (including breast, womb, and bowel cancer).
If you are concerned about your weight or how it may be affecting your health, speak to your GP. They can assess your health and discuss any appropriate support or treatment.
Childhood obesity
Childhood obesity is an important public health issue. Children living with obesity may be at greater risk of developing health conditions such as type 2 diabetes and cardiovascular disease, and are more likely to live with obesity as adults.
According to the National Child Measurement Programme (NCMP) figures for England, 10.5% of children aged four to five (reception) and 22.2% of children aged 10 to 11 (year 6) were living with obesity.
If you are concerned about your child's weight, speak to your GP or another healthcare professional before making significant changes to their diet. They can help you understand whether your child's weight may be affecting their health and advise you on appropriate support.
As a parent or carer, you can support healthy habits as a family by encouraging a balanced diet and regular physical activity. If your child is worried about their weight, listening to their concerns and approaching conversations about weight sensitively can help them feel supported.
What can cause obesity?
Obesity is complex and can develop for many reasons. It can happen when the body regularly takes in more energy from food and drink than it uses, storing the excess as fat. However, diet and physical activity are only part of the picture. Genetics, health conditions, certain medicines, age and circumstances can also affect weight.
Diet and physical activity
Eating and drinking more calories than your body uses over time can contribute to weight gain. Foods and drinks that are high in fat or sugar, larger portion sizes and drinking too much alcohol can all increase calorie intake.
Physical activity also affects how much energy your body uses. Some people may find it harder to be active because of their health, disability, mobility, or other circumstances.
Genetics and health
Genetics can affect how likely someone is to gain weight, and some health conditions can make it harder to maintain a healthy weight. These include an underactive thyroid and Cushing's syndrome.
Certain medicines, including some steroids, antidepressants and beta blockers, can also contribute to weight gain. If you are concerned that a medicine may be affecting your weight, speak to your GP or pharmacist. Do not stop taking prescribed medicine without speaking to a healthcare professional first.
Age and hormonal changes, including those associated with menopause and perimenopause, can also affect weight.
Social and economic factors
Where we live, our income and access to affordable, nutritious food and opportunities to be physically active can all influence our health and weight.
Sleep and wellbeing
Sleep and mental wellbeing may also play a part. Poor sleep can affect food choices, activity levels and mood, while some mental health conditions can make maintaining a healthy weight more difficult.
What treatments are available for obesity?
Treatment and support for obesity will depend on your individual circumstances and health. Your GP can discuss suitable options with you and, where appropriate, refer you to weight management or specialist services.
Treatment and support may include:
- Lifestyle support. Your GP may recommend changes to diet and physical activity, sometimes as part of a structured weight management programme.
- Other weight management options. Depending on your individual circumstances and health, other treatment options may be available. The NHS has further information about obesity treatment and support.
Speak to your GP if you would like support with your weight or want to understand which treatment options may be suitable for you.
How can a nutritionist support people living with obesity?
A nutritionist can offer personalised support to help you understand your eating habits and make sustainable changes to your diet.
Depending on your individual needs, they may help with:
- understanding what a balanced, nutritious diet looks like for you;
- identifying realistic and sustainable changes to your eating habits and lifestyle;
- exploring your relationship with food and factors that may influence how and what you eat;
- setting realistic, achievable goals;
- developing strategies to support long-term changes;
- reviewing your progress and adapting their recommendations where needed.
Different nutritionists have different training and areas of expertise. Some may specialise in supporting people living with obesity or related health conditions, while appropriately trained practitioners may also provide nutritional support before or after bariatric surgery.
What happens when you see a nutritionist?
Your first consultation will usually involve discussing your diet, lifestyle, health and any factors that may be affecting your eating habits. This helps the nutritionist understand your individual needs and the type of support that may be appropriate for you.
You may be asked to keep a food diary before or after your first consultation, noting what you eat and drink, along with other relevant information. Your nutritionist may also ask about your physical activity, emotional wellbeing, dietary requirements and any health conditions or medicines that could be relevant.
Based on this information, they can work with you to identify realistic dietary changes and develop an approach that considers your individual needs, preferences, and circumstances.
Ongoing nutrition support
Regular consultations can provide an opportunity to discuss what's working for you, any challenges you're experiencing and whether your approach needs to be adjusted. The type and frequency of support will depend on your individual needs.
If your needs fall outside their area of expertise or require medical assessment or treatment, your nutritionist should encourage you to seek appropriate support from your GP or another healthcare professional.
If you're ready to seek nutritional support, you can search for a nutrition professional with experience in supporting people living with obesity.
