What Is Obesity?

Obesity means having more body fat than your body needs, enough to raise the risk to your health. In the UK the line is a BMI of 30 or more. The World Health Organization classifies obesity as a chronic, relapsing disease that grows out of genes, brain biology, eating behaviour, access to a healthy diet and the wider environment.

The NHS lists the things that most often lie behind it:

• eating and drinking more energy than your body uses over time
• too little physical activity to use up the energy from food and drink
• genes that make you more likely to gain weight
• a health condition that causes weight gain, such as an underactive thyroid or Cushing’s syndrome
• some prescription medicines
• depression, an eating disorder or another mental health condition
• being over 55, or going through the perimenopause or menopause

You can check with two measurements: your BMI and your waist. A BMI of 30 or more is in the obese range for most adults, and 25 to 29.9 is overweight. The NHS BMI calculator works it out from your height and weight. Obesity also tends to show in daily life, and these are the signs a clinician looks at:

• a BMI of 30 or more, or 27.5 or more for people from higher-risk ethnic backgrounds
• a waist that is more than half your height
• breathlessness
• difficulty moving around
• feeling very tired
• joint and back pain
• snoring
• feeling very low

None of these signs belongs to obesity alone, so each is worth raising with a clinician in its own right.

NICE sorts adult BMI into bands, and obesity itself into three classes.

• healthy weight: BMI 18.5 to 24.9
• overweight: BMI 25 to 29.9
• obesity class 1: BMI 30 to 34.9
• obesity class 2: BMI 35 to 39.9
• obesity class 3: BMI 40 or more

Class 3 obesity is the band sometimes still called morbid obesity. NICE asks clinicians to use judgement at every level: a person in the healthy weight band can still carry too much fat around the middle, and the classes above it are a guide to health risk and to which NHS services are available to you. The weight management glossary explains each term.

Each of these numbers marks the start of an obesity class, and each changes the NHS support you can be offered.

• BMI 30 starts obesity class 1. With diabetes or high blood pressure, it is the threshold for the free 12-week NHS Digital Weight Management Programme, which your GP surgery refers you to.
• BMI 35 starts class 2. Below it, NICE recommends measuring waist-to-height ratio alongside BMI, because BMI alone misses fat around the middle.
• BMI 40 starts class 3, the band sometimes still called morbid obesity, where specialist NHS services are most likely to be involved.

For people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds, each of these thresholds sits 2.5 points lower, at 27.5, 32.5 and 37.5.

If you are from a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, the UK uses lower BMI thresholds: 23 to 27.4 is overweight and 27.5 or more is obesity. NICE sets these because people from these backgrounds tend to store more fat around the middle, so the risk of type 2 diabetes, high blood pressure and heart disease begins at a lower BMI.

The higher obesity classes move down by the same 2.5 points, so class 2 starts at 32.5 and class 3 at 37.5. Waist-to-height ratio uses the same cut-offs for everyone, which makes it a useful second check whatever your background.

BMI is a useful first measure that cannot tell muscle from fat, so NICE advises reading it with caution. It can put a muscular person in the obese range with little body fat, it can miss fat stored around the organs in someone of ordinary weight, and it needs care in people aged 65 and over.

That is why NICE pairs it with waist-to-height ratio for anyone with a BMI under 35. Measure your waist halfway between your lowest rib and the top of your hips, breathing out normally, and divide it by your height. A result of 0.5 to 0.59 means increased fat around the middle and 0.6 or more means high, so aim to keep your waist under half your height. NICE also advises against using the body fat reading from smart scales, which rely on bioimpedance, in place of BMI. The visceral fat page covers fat around the organs in more detail.

NHS support for obesity is organised in four tiers, each more specialist than the last.

• Tier 1 is prevention for everyone: healthy-living advice from GPs, practice nurses, pharmacists and public health teams.
• Tier 2 is lifestyle weight management, usually a group programme of around 12 weeks on food, activity and behaviour change, paid for by your local council.
• Tier 3 is a specialist weight management service for complex obesity, with dietitians, psychological support and activity guidance, typically lasting 6 months to 2 years.
• Tier 4 is bariatric surgery in hospital, with preparation beforehand and long-term follow-up.

You can refer yourself to some weight management programmes, and your GP can refer you to a specialist service if you need more support. A loss of about 5 per cent of body weight, held, already improves blood pressure, blood sugar and cholesterol.

An obesity clinic is a specialist weight management service, and in London you can reach one through the NHS or privately. On the NHS, the specialist tier 3 services take referrals from GPs, and what is available varies by area. Your GP surgery or your integrated care board website lists the services near you.

Privately, you can book an assessment without a referral. Before you book anywhere, check that the first appointment includes a full history, blood pressure and the right blood tests, and that there is a plan for follow-up. The medical weight loss programme page sets out what a clinical programme should contain.

See your GP if your BMI is in the overweight or obese range and you want help to lose weight, if your waist is more than half your height, or if you have prediabetes, diabetes, high blood pressure, high cholesterol, joint pain, sleep apnoea or heart disease. The NHS also suggests seeing a GP if obesity runs in your family. If you have put on weight quickly without a change in how you eat or move, start with your GP: the unexplained weight gain page lists the medical causes they check. If eating or your weight is causing you distress, or you think you may have an eating disorder such as binge eating, speak to your GP or contact Beat on 0808 801 0677.

A first assessment arranged by Medical Weight Loss London at UNTIL Soho measures your height, weight, waist and blood pressure, and arranges the blood tests that show how your weight is affecting your health: HbA1c, a lipid profile, liver and kidney function, thyroid function and a full blood count. It also asks about sleep, mood, medicines and your relationship with food. First assessments at London clinics cost about £150 to £310, with tests on top (what a programme costs).

Ask what to get checked and UNTIL Health Concierge arranges the appointment with a registered clinician.