Obesity

Obesity is a long-term condition in which a person carries excess body fat to a degree that can affect their health. It is most often assessed using body mass index (BMI), a measure based on height and weight, alongside other measures such as waist size, which gives an idea of fat carried around the middle.

BMI is a useful screening tool but it is not perfect, because it does not directly measure body fat or take account of muscle, build or ethnicity. For this reason, clinicians look at the whole picture, including waist measurement and overall health, rather than relying on a single number.

Obesity develops when, over time, the body takes in more energy from food and drink than it uses, and the surplus is stored as fat. But this balance is shaped by far more than willpower. Genetics, hormones, sleep, stress, mental health, some medicines and certain medical conditions can all make weight gain more likely or weight loss harder.

The environment also plays a large part, including easy access to high-calorie food, large portion sizes and daily routines that involve a lot of sitting. Because so many factors interact, obesity is best understood as a complex health condition rather than a simple matter of personal choice.

Carrying excess weight increases the risk of a number of conditions, including type 2 diabetes, high blood pressure, high cholesterol, heart disease and stroke, several types of cancer, fatty liver disease, gallstones, joint problems such as osteoarthritis, and breathing problems including obstructive sleep apnoea.

Obesity can also affect mood and quality of life, and many people experience weight-related stigma, which can make things harder. The good news is that losing even a modest amount of weight, and keeping it off, can improve blood pressure, blood sugar, cholesterol and joint symptoms.

Obesity is usually assessed by measuring height and weight to work out BMI, and by measuring waist size. These give an estimate of body fat and of the health risks linked to where fat is stored. The thresholds used can differ for some ethnic groups, who may face higher risk at a lower BMI.

A clinician may also ask about your medical history, lifestyle, mood and any medicines, and check for related conditions such as raised blood pressure, blood sugar or cholesterol. Sometimes blood tests are arranged to look for these and to rule out underlying causes. This assessment helps shape a plan that suits you.

The foundation of treatment is support to build sustainable habits around eating, physical activity and behaviour, ideally with the help of a structured programme or healthcare team. Realistic, gradual changes that can be maintained tend to work better than very restrictive short-term diets, and even modest weight loss can bring health benefits.

For some people, medicines that support weight loss may be considered alongside lifestyle changes. Weight-loss (bariatric) surgery is an option for certain people with more severe obesity or weight-related health problems, when other approaches have not been enough. Any treatment is usually combined with ongoing support, because keeping weight off is a long-term effort.

Healthy habits help prevent weight gain and support long-term health: a balanced diet with plenty of vegetables, fruit and fibre, being physically active most days, getting enough sleep, managing stress and limiting sugary drinks and ultra-processed foods. Small changes that fit your life and can be kept up are more effective than drastic ones.

Obesity is a long-term condition, and weight can change over time, so ongoing support and review are valuable rather than a one-off effort. With the right help, many people improve their health, lower their risk of related conditions and feel better, even if their weight does not reach an ideal number.