Keep your waist to less than half your height, guidance says
People should be encouraged to measure their waist to check they don't have too much dangerous fat around their middle, updated guidelines say.
An adult's waist should be less than half their height to reduce health risks, health body NICE recommends.
Measuring body mass index (BMI) is also useful - but doesn't take into account excess weight around the abdomen.
This increases the risk of conditions such as type 2 diabetes, high blood pressure, heart disease and stroke.
New draft guidance from the National Institute for Health and Care Excellence (NICE) says people from some Asian and black ethnic groups are more prone to this type of fat build-up around the waist, which is called "central adiposity".
They should use lower BMI thresholds for obesity to help predict their specific health risks.
But NICE warns that even those in a healthy BMI weight category could be carrying too much weight around the waist.
"Explain to people that to measure their waist, they should find the bottom of their ribs and the top of their hips, wrap a tape measure around the waist midway between these points and breathe out naturally before taking the measurement," say the guidelines on identifying people who are overweight and obese.
If you're 175cm (5ft 9 inches) tall, for example, then your waist measurement should be less than 87.5cm (34 inches) - or half your height.
Measuring waist-to-height ratio can be used for both sexes and all ethnic groups, as well as highly muscular adults, it adds.
But waist circumference measurements are not accurate in people with a BMI over 35, pregnant women or children under two.
The latest estimates for England suggest that 28% of adults are obese and a further 36% are overweight - a problem that is costing the NHS more than £6bn.
Professor Naveed Sattar, professor of metabolic medicine at the University of Glasgow, said whether this new message gets taken up is "uncertain" but he said it never harms to try "new ways" to get people to think about their health.
Other experts say measuring the waistline doesn't work for people who are very short or older people over 60 who may have lost height with ageing.
But Professor Rachel Batterham, consultant in obesity, diabetes and endocrinology, who is on the guidelines committee, said: "Increased fat in the abdomen increases a person's risk of developing several life-limiting diseases including type 2 diabetes and heart disease.
"Waist-to-height ratio is a simple, easy-to-use measure that identifies people who are at increased health risk and would benefit from weight management support to improve their health."
In the guidance, GPs and nurses are advised to ask someone's permission before talking about their weight, and also to "discuss it in a sensitive manner".
Advice on managing weight is usually tailored to the individual and focuses on improving their diet and getting them to exercise more, in addition to potential treatments and surgery.
Dr Paul Chrisp, director of the centre for guidelines at NICE, said the updated draft guidelines help people understand what factors affect their health and how to address them.
Healthcare professionals and the public can comment on the proposed recommendations in the guidelines before they are published in May.
The updated guidelines say doctors should also consider using waist-to-height ratio in children and young people aged over five to assess and predict health risks.
During the pandemic, there was a substantial rise in obesity in children in England with 25% classed as obese by the time they leave primary school, according to recent NHS data.
Dr Nivedita Aswani, consultant paediatrician specialising in diabetes and weight management at Sheffield Children's Hospital, said even young children were at risk of the effects of fat in the abdomen.
What is a healthy body mass index (BMI)?
healthy weight: BMI 18.5 kg/m2 to 24.9 kg/m2
overweight: BMI 25 kg/m2 to 29.9 kg/m2
obesity class 1: BMI 30 kg/m2 to 34.9 kg/m2
obesity class 2: BMI 35 kg/m2 to 39.9 kg/m2
obesity class 3: BMI 40 kg/m2 or more
Source: Phillipa Roxby, BBC News Health Reporter