Obesity and your health
Obesity raises the risk of type 2 diabetes, high blood pressure, heart disease, sleep apnoea and 13 types of cancer. This guide gives the BMI bands, the waist measure NICE recommends and the changes a 5% or 10% weight loss brings.
In short: In England, 64% of adults live with overweight or obesity and 29% live with obesity (Health Survey for England 2022). NICE defines obesity as a BMI of 30 or more, or 27.5 or more for some ethnic backgrounds. Losing 5% of body weight improves blood sugar and systolic blood pressure. Sleep apnoea, liver inflammation and heart outcomes generally need 10% or more.
How common obesity is in England #
The Health Survey for England 2022 measured adults aged 16 and over. 64% were living with overweight or obesity, and 29% with obesity. Men were more likely to be above a healthy weight: 67% against 61% of women. Obesity rates were close, at 28% of men and 30% of women.
Where you live matters. Obesity affected 36% of adults in the most deprived fifth of areas and 22% in the least deprived. The rate has stayed at about 28% to 29% since 2017, up from about 15% in 1993.
BMI bands for adults #
BMI is your weight in kilograms divided by your height in metres squared. NICE guideline NG246 uses the bands below. Check yours with the BMI calculator.
| Band | BMI | BMI for the backgrounds listed below |
|---|---|---|
| Healthy weight | 18.5 to 24.9 | 18.5 to 22.9 |
| Overweight | 25 to 29.9 | 23 to 27.4 |
| Obesity class 1 | 30 to 34.9 | 27.5 or more counts as obesity |
| Obesity class 2 | 35 to 39.9 | Thresholds usually 2.5 lower |
| Obesity class 3 | 40 or more | Thresholds usually 2.5 lower |
The lower thresholds apply to people with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background. NICE sets the overweight line at 23 and the obesity line at 27.5 for these groups.
Waist-to-height ratio from NICE #
NICE recommends waist-to-height ratio for adults with a BMI under 35. Divide your waist by your height, using the same units. The measure works for both sexes and all ethnic backgrounds.
- 0.4 to 0.49: healthy central adiposity, no increased health risk.
- 0.5 to 0.59: increased central adiposity, increased health risk.
- 0.6 or more: high central adiposity, further increased risk.
Keep your waist to less than half your height. A person 170 cm tall should aim for a waist under 85 cm. In the 2022 survey, 71% of men and 62% of women in England had a ratio above 0.5.
How excess weight affects the body #
Risk rises with BMI and with waist size. These figures come from UK public health bodies.
- Type 2 diabetes: adults with obesity are 5 times more likely to develop the condition (Public Health England).
- High blood pressure: more than 2.5 times more likely, which raises the risk of heart disease and stroke. See GLP-1 medicines and blood pressure.
- Cancer: overweight and obesity cause more than 1 in 20 UK cancer cases and are linked to 13 types, including breast, bowel, womb, kidney, liver and pancreatic cancer (Cancer Research UK).
- Sleep apnoea: NHS England counts obstructive sleep apnoea among the 5 weight-related conditions used to prioritise NHS treatment. Read sleep and weight.
- Joints and liver: the NHS links obesity to osteoarthritis and fatty liver disease, plus day-to-day breathlessness, snoring and back pain.
- Fertility: studies in women with polycystic ovary syndrome show ovulation improving after modest weight loss.
What a 5% and 10% weight loss changes #
A 2017 review by Ryan and Yockey in Current Obesity Reports mapped health gains against the amount of weight lost. For a person weighing 100 kg, 5% means 5 kg and 10% means 10 kg.
| Condition | At about 5% | At 10% or more |
|---|---|---|
| Type 2 diabetes risk | 58% fewer new cases at an average 6.7% loss (Diabetes Prevention Program) | Each extra kilogram cut risk by 16%, up to about 10 kg |
| Blood sugar in type 2 diabetes | Fasting glucose and HbA1c improve from a 2% to 5% loss | Further improvement with each step |
| Blood pressure | Systolic pressure improves from a 2% to 5% loss | Diastolic pressure improves at 5% to 10% |
| Blood fats | Triglycerides improve from a 2% to 5% loss | HDL cholesterol improves at 5% to 10% |
| Sleep apnoea | Little change | Clear improvement needed a loss of 10 kg or more |
| Knee osteoarthritis | Pain and walking improve at 5.7%. Each pound lost removes about 4 pounds of knee load per step | Inflammation markers fall |
| Liver fat | Falls by 13% | Falls by 52% at an 11% loss and 65% at 16% |
| Heart attack and stroke | No reduction shown | 21% fewer major events after a 10% loss in year 1 (Look AHEAD) |
| Ovulation in PCOS | Improves from a 2% to 5% loss | More consistent at 5% to 10% |
Most figures come from diet and activity programmes, and several studied people with type 2 diabetes. The Look AHEAD heart finding came from a later analysis, not the main trial result.
Why obesity is treated as a long-term condition #
Weight tends to return when treatment stops. Two trials measured the size of the regain.
- STEP 1 tested semaglutide 2.4 mg weekly for 68 weeks alongside diet and activity support. Average loss was 14.9%. Participants followed for a further year off treatment ended 5.6% below starting weight.
- SURMOUNT-4 tested tirzepatide 10 mg or 15 mg weekly with lifestyle counselling. Participants lost 20.9% in 36 weeks. Those switched to placebo regained 14.0% over the next 52 weeks. Those who continued lost a further 5.5%.
NICE tells services to offer support with keeping weight off whenever a medicine stops. Plan for the long term with a maintenance plan, and check your eligibility if medicine is an option for you.
Obesity and your health: questions #
What BMI counts as obese in the UK?
NICE classes a BMI of 30 or more as obesity. Class 1 runs from 30 to 34.9, class 2 from 35 to 39.9 and class 3 starts at 40. For people with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, obesity starts at 27.5 and overweight at 23.
Is waist size a better measure than BMI?
NICE recommends using both when your BMI is under 35. Waist-to-height ratio shows fat carried around your middle, which BMI misses. A ratio of 0.5 to 0.59 signals increased health risk and 0.6 or more signals further increased risk. Aim to keep your waist under half your height.
How much weight do I need to lose to improve my health?
Aero’s treatment prices are not yet confirmed. Before paying, ask for the total price, pack quantity, prescribing fees, dispensing and delivery charges, and follow-up costs. Use your provider’s written quote in the cost planner.
Why is the BMI threshold lower for some ethnic groups?
Some ethnic groups experience weight-related health risks at a lower BMI. NICE therefore uses lower assessment thresholds for specified backgrounds. A clinician should interpret BMI alongside other health information; medicine licensing and NHS treatment criteria need to be checked separately.
Does weight come back after stopping weight loss medicine?
Usually, yes. In SURMOUNT-4, adults who lost 20.9% on tirzepatide over 36 weeks with lifestyle counselling regained 14.0% in the 52 weeks after switching to placebo. After STEP 1, people followed for a year off semaglutide ended 5.6% below starting weight. NICE recommends ongoing support when a medicine stops.
Understand your treatment options
Explore the treatment guides and prepare your questions for a clinician. Aero’s prices and service details will be confirmed before booking opens.
Page information
- Summary
- How obesity affects your body, the NICE BMI bands and waist-to-height ratio, and the health changes a 5% or 10% weight loss brings. Explore the full guide.
- Publisher
- Aero Clinic, operated by AERO HEALTHCARE LTD.
- Editorial update
- Clinical review
- Pending. An editorial update is not a clinical sign-off.
Cite as: Obesity and your health, Aero Clinic (https://www.cagri.co.uk), AERO HEALTHCARE LTD. https://www.cagri.co.uk/obesity-and-health. Editorial update: 4 November 2026. Clinical review pending.