Doctors define obesity based on body mass index (BMI), calculated from weight and height. Obesity increases the risk of many health problems and can make it harder to move, breathe and do everyday activities.
How is obesity defined?
For people who are White, Hispanic or Black, 'overweight' means a BMI between 25 and 29.9, and 'obesity' means a BMI of 30 or greater. For people of Asian background the cut-offs are lower: overweight is a BMI of 23–25 and obesity is 25 or above. Your doctor may also measure your waist circumference — extra weight around the belly is called 'central obesity' and carries its own risks, even if BMI is normal.
Health risks of obesity
Obesity increases the risk of diabetes, high blood pressure, high cholesterol, heart disease and heart attacks, stroke, sleep apnoea, asthma and several cancers. It can also make everyday movement, breathing and physical activity more difficult.
Does obesity shorten life?
Studies show that people with obesity, on average, die younger than people at a healthy weight, and the risk rises with higher weight and longer duration of obesity. Central obesity is also linked to earlier death, even in people whose BMI is not very high.
Can medical treatments help me lose weight?
Yes. Prescription medicines and weight-loss surgery are options for people who have not been able to lose weight with lifestyle changes alone. These treatments do not replace healthy eating and physical activity — they work alongside them.
How to lower your risk
Even if losing weight is difficult, you can improve your health by becoming more active (start with a few minutes a day and build up), improving your diet with more vegetables and fruit and fewer processed foods, quitting smoking if you smoke, and limiting alcohol. Keeping a simple diary of what you eat, your activity and your weight can help you stick to your goals.
What causes obesity?
Genes influence risk, but lifestyle plays a major role. Eating too much, eating unhealthy foods and moving too little all contribute. Other factors include a mother's habits during pregnancy, weight gain in childhood or adolescence, insufficient sleep, certain long-term medications, and hormonal conditions such as hypothyroidism.
Obesity, pregnancy and children
Being overweight or having obesity can make it harder to conceive. In males, obesity can also contribute to erectile problems, especially alongside high blood pressure or diabetes. In children, obesity carries similar risks — diabetes, high blood pressure, asthma, sleep apnoea — and can affect growth and puberty.
When to see your doctor
Speak to your doctor or nurse if you want to lose weight — they can help you do it safely. A dietitian can also help you plan meals and choose the right foods.
Key takeaways
- Obesity is usually defined by BMI, but waist size and central obesity also matter.
- It increases the risk of diabetes, heart disease, stroke, sleep apnoea, cancer and earlier death.
- Even without major weight loss, activity and diet changes improve health.
- Medicines and surgery are options for some people alongside lifestyle changes.