Obesity

What is obesity?

Obesity means carrying more body fat than is healthy for you, to the point where it starts to affect your health. It develops when your body stores extra calories as fat over time, and it's recognised as a long-term, complex health condition rather than a lifestyle choice.

What are the symptoms of obesity?

Obesity is measured rather than felt, so the clearest signs come from physical measurements and how carrying excess weight affects your day-to-day life.

You can check whether you're living with overweight or obesity using:

• your body mass index (BMI), which divides your weight in kilograms by your height in metres squared. For most adults, a BMI of 25–29.9 means you're overweight, and 30 or more means you're living with obesity
• lower thresholds if you're from a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, since health risks can appear at a lower BMI: 23–27.4 is overweight, and 27.5 or higher is obesity
• your waist-to-height ratio, if your BMI is under 35. As a guide, try to keep your waist size to less than half your height.

Living with obesity can also bring day-to-day effects, including:

• breathlessness
• difficulty moving around
• persistent tiredness
• joint and back pain
• snoring
• low mood or other mental health difficulties.

What are the causes of obesity and who is at risk?

At its simplest, obesity develops when you take in more calories from food and drink than your body burns off. But your risk of developing it is shaped by much more than diet alone.

You may find it harder to stay a healthy weight if you:

• are not very physically active
• eat and drink more than your body needs, particularly food that is high in fat and sugar
• have an eating disorder or another mental health condition, such as depression
• have a health condition, disability or learning disability that makes exercise difficult
• have a hormone-related condition, such as an underactive thyroid gland, Cushing's syndrome or Polyendocrine metabolic ovarian syndrome (PMOS), previously known as polycystic ovary syndrome (PCOS)
• take certain medicines, including some steroids, antidepressants and beta blockers
• have inherited genes that make weight gain more likely. More than 40 places in the human genome have been linked to obesity, and 80% of children with two parents living with obesity also develop it themselves, compared with fewer than 10% of children whose parents are both a healthy weight
• are over 55, or are menopausal or perimenopausal

Wider environmental factors matter too, including easy access to energy-dense food and daily lives that involve less physical activity than in the past.

Are there different types of obesity?

Obesity isn't usually divided into separate types. Instead, it's graded by how high your BMI is, which gives a guide to how much extra health risk it's likely to carry:

• class 1 obesity: BMI of 30–34.9
• class 2 obesity: BMI of 35–39.9
• class 3, or severe, obesity: BMI of 40 or over.

Children and teenagers are assessed differently from adults, using measurements that account for their age and sex, since a healthy BMI changes as children grow.

How is obesity diagnosed?

Obesity is diagnosed by measuring your height and weight and calculating your BMI. BMI can't tell fat and muscle apart, though, so if you carry a lot of muscle, it may place you in the overweight or obese category even without excess body fat.

Because of this, your waist-to-height ratio may be used alongside your BMI, particularly if your BMI is under 35, to give a clearer picture of how much fat you're carrying around your middle. Body fat percentage, measured in specialist settings, is sometimes used as a more precise alternative to BMI.

How is obesity treated?

Non-surgical treatment

The main non-surgical treatment for obesity is changing your diet and activity levels so you burn more calories than you take in. On average, women need around 2,000 calories a day and men around 2,500, though this varies from person to person.

Lifestyle changes that can help include:

• keeping meals lower in fat and sugar, with more fruit and vegetables
• aiming to lose weight steadily, around 1–2lbs (0.5–1kg) a week
• cutting down on alcohol, which is high in calories
• staying active for 45–60 minutes a day, split into shorter sessions if that's easier
• setting realistic goals and weighing yourself regularly to track progress.

If you need more support, your GP can refer you to a weight management programme, which may include one-to-one coaching, cognitive behavioural therapy (CBT), group support or online exercise classes, and some services can be accessed without a GP referral first. A small number of people are supported by a dietitian to follow a very low-calorie diet of 800–1,200 calories a day, though this isn't suitable or safe for everyone.

You may also be offered weight-loss medicines alongside diet and lifestyle changes:

• emaglutide, liraglutide and tirzepatide reduce your appetite and help you feel fuller for longer
• orlistat reduces the amount of fat your body absorbs from food.

You'll need to keep to a balanced, lower-calorie diet and stay active while taking these medicines, and you should be offered support to maintain a healthy weight after you stop.

Surgical treatment

Weight-loss surgery, also called bariatric surgery, makes your stomach smaller so you eat less food. It's the most effective treatment for obesity and may be offered if your BMI is 40 or over, or 35 or over alongside another condition, such as type 2 diabetes or high blood pressure, that could improve with weight loss.

If you're from a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, surgery may be offered at a BMI of 37.5 or over, or 32.5–37.4 with a related health condition.

Types of weight-loss surgery include:

1. gastric banding, where an adjustable band is placed around the top of your stomach
2. gastric bypass, which reroutes part of your digestive system
3. sleeve gastrectomy, which removes part of your stomach
4. biliopancreatic diversion, a more complex procedure that also changes how your intestines absorb nutrients.

You'll typically be home within a couple of days, with recovery taking around 3–4 weeks, and you'll have regular check-ups for 2 years afterwards. As with any operation, complications are possible in some cases, and a small number of people need a further procedure.

When should I see a doctor?

See a GP if your BMI is in the overweight or obese range and:

• you'd like help losing weight
• your waist measures more than half your height
• you have pre-diabetes, diabetes, high blood pressure, joint pain, high cholesterol, sleep apnoea or cardiovascular disease
• you have a family history of obesity
• you have, or think you may have, an eating disorder, such as binge eating.