Can we trust BMI to measure obesity?

You’ve been using our fat calculator in your droves, working out your BMI (body mass index) and comparing the result with people in your age group and your part of the UK.

But a few people have been critical. They say using BMI to measure whether they are healthy, overweight or obese is misleading.

So what’s the truth? Can we trust what it tells us?

Is BMI the best measure of obesity?

Firstly, it is a quick and easy way of working out whether you are in the healthy category by using two simple measures – weight and height.

Most doctors say it is the best method they have, it’s pretty accurate, can be measured simply in clinic and is acceptable to patients.

If you can’t see the calculator tap or click here.

But does it work for everyone?

No, not all.

And this provoked a few comments along these lines: “Why, in this day and age, are you using BMI to tell people they are overweight? It is an outdated method that does not take into consideration muscle and actual health! I am extremely fit and healthy with a low body fat percentage, yet your BMI tells me (and many more self-conscious girls) that I am overweight!”

There are some people who carry a lot of muscle and little fat, like bodybuilders, boxers and rugby players.

Muscle is much denser than fat so they may end up with a BMI that classes them as obese, despite the fact they may be fit and healthy.

But this is thought to apply to fewer than 1% of the population. Most people aren’t extreme athletes.

Tim Cole, professor of medical statistics, at University College London Great Ormond Street Institute of Child Health, said BMI was “still extremely relevant”.

“You don’t see many bodybuilders around but you do see lots of people with large waists. Many people get exercised about that wrongly.”

As people age, they lose muscle and may be classed in the “healthy weight” range even though they may be carrying excess fat. This is particularly true of smokers.

BMI also doesn’t apply to pregnant women, and some ethnic groups have a higher risk of health problems at lower BMI levels.

Does BMI actually measure fat?

It can’t measure how much excess fat we have in our bodies – as opposed to muscle and bone – because that would require some pretty complicated and expensive medical procedures, which just aren’t practical to carry out on the whole population.

What it does do is give a healthy weight range for a particular height, taking into account variations in body shape – and it provides a good starting point for the majority of people.

It also doesn’t measure how fat is distributed throughout the body (some fat is ok; too much in the wrong place is a risk).

Research shows that people who carry a lot of fat around their waists are at higher risk of health problems than those with more fat around their thighs and buttocks.

They are more likely to have fat stored in their abdomen around key organs, which could increase the risk of heart disease, stroke and type 2 diabetes.

So waist size may be a better way to monitor your health than BMI. That’s why our calculator included an option for giving your waist size too.

“If people think they have lots of muscle mass, their waists should be lower for a given BMI – so they can easily check,” says Prof Sattar.

How to measure your waist

  • find the bottom of your ribs and the top of your hips
  • wrap a tape measure around your waist midway between these points
  • breathe out naturally before taking the measurement

    Regardless of your height or BMI, you should try to lose weight if your waist is:

    • men – 94cm (37ins) or more
    • women – 80cm (31.5ins) or more

      Can BMI tell us anything about disease risk?

      On its own, it can’t.

      But doctors use BMI in conjunction with other measures – like blood pressure, cholesterol and family history – to work out an individual’s risk of type 2 diabetes or heart disease, for example.

      Body mass index is not specific to any particular health risk – and that’s its strength, experts say.

      However, a BMI above the healthy range or too much fat around the waist is known to increase the risk of serious health problems, including stroke and certain cancers.

      Are we shaming those who are overweight?

      One person said of the BBC calculator: “Your unscientific method of calculating ‘fatness’ is an unhelpful tool that dehumanises those who are obese or overweight, shaming them into losing weight and threatening their fragile relationship with their bodies.”

      There was no intention of shaming people – merely offering a way of finding out about your own weight because excess fat is the cause of an increased risk of a range of diseases.

      If you think you would like to lose some weight, you should go and see your GP for advice first.

      The best way to lose weight is to make small, realistic changes to your diet and physical activity.

      View comments

Rise in cancers ’caused by weight’

Being overweight or obese is a growing cause of cancer in the UK while cases caused by smoking are falling, according to a large study.

Cancer Research UK found more than a third of all cases of cancer were avoidable – some 135,000.

The charity also found that excess weight now caused 6.3% of all cancer cases – up from 5.5% in 2011 – while smoking as a cause had declined.

It said more action was needed to tackle the “health threat” of obesity.

  • Millennials ‘set to be fattest generation’
  • World’s children rapidly turning obese

    Cancer Research UK found the country with the greatest proportion of preventable causes of cancer was Scotland with 41.5%, followed by Northern Ireland on 38%, Wales on 37.8%, and England on 37.3%.

    Across the UK, smoking remained by far the leading cause of preventable cancer, although it dropped from 19.4% in 2011 to 15.1%.

    Second was being overweight or obese, and third was exposure to UV radiation from the sun and sunbeds.

    The standard way of diagnosing if someone is obese is by calculating their body mass index (BMI). It measures whether you’re a healthy weight for your height.

    A BMI of more than 25 means you’re overweight and a BMI of more than 30 means you’re classified as obese, although there are some exceptions.


    ‘I felt responsible’

    Janet Boak, from Carlisle, was diagnosed with womb cancer at 51, after she noticed spots of blood four years after her menopause.

    She had a full hysterectomy, which successfully removed the cancer.

    It was during a subsequent check-up that she was told being obese had contributed to her risk of getting cancer. At the time, she was nearly 20 stone.

    “I felt like I was responsible for my own downfall,” Janet, 55, said.

    “It stuck in my gut a bit, thinking I could maybe not have been in this position had I sorted my lifestyle out.”

    Janet, a grandmother, has since lost nearly seven stone after she cut down on sugar, started cooking healthier meals from fresh ingredients and became more active.


    Cancer Research UK found overexposure to UV radiation caused about 13,600 cases of melanoma skin cancer a year – or 3.8% of all cancer cases.

    Other preventable causes of cancer included drinking alcohol and eating too little fibre, it said.

    However, overall the analysis found the proportion of preventable cases of cancer had fallen – from 42.7% in 2011 to 37.7%.

    Cancer Research UK said the figures showed smoking prevention strategies were working, but more work was needed to tackle the growing problem of obesity.

    Prof Linda Bauld, Cancer Research UK’s prevention expert, said: “Obesity is a huge health threat right now, and it will only get worse if nothing is done.

    “The UK government must build on the successes of smoking prevention to reduce the number of weight-related cancers.

    “Banning junk food TV adverts before the 21:00 GMT watershed is an important part of the comprehensive approach needed.”

    Prof Mel Greaves, a cancer biologist at the Institute of Cancer Research, in London, said the study was an “endorsement” of the idea that many cancers were potentially preventable.

    But he said the idea that obesity itself or eating too little fibre “causes” cancer was “somewhat simplistic” and still needed to be explored further.

    “If obesity could be avoided, the impact on cancer rates is uncertain – but they would almost certainly decline significantly,” Prof Greaves said.

    “Given the currently high rates of obesity in young people, this represents (like cigarette smoking) a major societal challenge beyond the bounds of the medical arena.”

    View comments

Rise in cancers ’caused by weight’

Being overweight or obese is a growing cause of cancer in the UK while cases caused by smoking are falling, according to a large study.

Cancer Research UK found more than a third of all cases of cancer were avoidable – some 135,000.

The charity also found that excess weight now caused 6.3% of all cancer cases – up from 5.5% in 2011 – while smoking as a cause had declined.

It said more action was needed to tackle the “health threat” of obesity.

  • Millennials ‘set to be fattest generation’
  • World’s children rapidly turning obese

    Cancer Research UK found the country with the greatest proportion of preventable causes of cancer was Scotland with 41.5%, followed by Northern Ireland on 38%, Wales on 37.8%, and England on 37.3%.

    Across the UK, smoking remained by far the leading cause of preventable cancer, although it dropped from 19.4% in 2011 to 15.1%.

    Second was being overweight or obese, and third was exposure to UV radiation from the sun and sunbeds.

    The standard way of diagnosing if someone is obese is by calculating their body mass index (BMI). It measures whether you’re a healthy weight for your height.

    A BMI of more than 25 means you’re overweight and a BMI of more than 30 means you’re classified as obese, although there are some exceptions.


    ‘I felt responsible’

    Janet Boak, from Carlisle, was diagnosed with womb cancer at 51, after she noticed spots of blood four years after her menopause.

    She had a full hysterectomy, which successfully removed the cancer.

    It was during a subsequent check-up that she was told being obese had contributed to her risk of getting cancer. At the time, she was nearly 20 stone.

    “I felt like I was responsible for my own downfall,” Janet, 55, said.

    “It stuck in my gut a bit, thinking I could maybe not have been in this position had I sorted my lifestyle out.”

    Janet, a grandmother, has since lost nearly seven stone after she cut down on sugar, started cooking healthier meals from fresh ingredients and became more active.


    Cancer Research UK found overexposure to UV radiation caused about 13,600 cases of melanoma skin cancer a year – or 3.8% of all cancer cases.

    Other preventable causes of cancer included drinking alcohol and eating too little fibre, it said.

    However, overall the analysis found the proportion of preventable cases of cancer had fallen – from 42.7% in 2011 to 37.7%.

    Cancer Research UK said the figures showed smoking prevention strategies were working, but more work was needed to tackle the growing problem of obesity.

    Prof Linda Bauld, Cancer Research UK’s prevention expert, said: “Obesity is a huge health threat right now, and it will only get worse if nothing is done.

    “The UK government must build on the successes of smoking prevention to reduce the number of weight-related cancers.

    “Banning junk food TV adverts before the 21:00 GMT watershed is an important part of the comprehensive approach needed.”

    Prof Mel Greaves, a cancer biologist at the Institute of Cancer Research, in London, said the study was an “endorsement” of the idea that many cancers were potentially preventable.

    But he said the idea that obesity itself or eating too little fibre “causes” cancer was “somewhat simplistic” and still needed to be explored further.

    “If obesity could be avoided, the impact on cancer rates is uncertain – but they would almost certainly decline significantly,” Prof Greaves said.

    “Given the currently high rates of obesity in young people, this represents (like cigarette smoking) a major societal challenge beyond the bounds of the medical arena.”

    View comments

A blueberry muffin ‘could have day’s worth of sugar’

Some blueberry muffins sold by cafes and supermarkets contain more than the recommended daily intake of sugar for adults, researchers have discovered.

An analysis by Action on Sugar and the Obesity Health Alliance in January found the cakes could contain up to eight teaspoons of sugar.

The recommended daily limit for adults is seven – for children it is less.

Health experts said the findings showed it was “all too easy” to consume “huge” amounts of sugar.

  • ‘Limit children’s snacks to 100 calories’
  • Kids devouring ‘breakfast sugar’

    ‘Limited labelling’

    Action on Sugar and the Obesity Health Alliance, which looked at 28 muffins sold in food outlets in train stations and supermarkets, found 61% of them contained six teaspoons of sugar or more – the upper daily limit for a child aged seven-to-10 years old.

    They also found muffins bought at train station food retailers had 19% more sugar per portion and were 32% bigger than those bought in supermarkets.

    There was also a big variation, with muffins from Marks and Spencer containing just three teaspoons.

    Caroline Cerny, from the Obesity Health Alliance, said: “We may think grabbing a blueberry muffin is a reasonably healthy option for a snack on the go compared to other cakes or a chocolate bar – yet the figures suggest otherwise.

    “There is huge variation in both the size of muffins and the sugar content, and with limited nutrition labelling, it’s all too easy to eat a huge amount of sugar in just one serving.”

    The research also found a lack of nutrition labelling on a number of muffins, both those sold in stations and in supermarkets.

    The two organisations are now calling for manufacturers to reduce sugar in line with the government’s plans to cut it by 20% in common products by 2020.

    They are also calling for front-of-pack “traffic-light” nutrition labelling to be mandatory across all products, including the out-of-home sector.

    The British Retail Consortium, which represents food retailers, said its members were “actively engaged” in Public Health England’s sugar reduction strategy and had removed thousands of tonnes of sugar in products such as bakery items.

    Andrea Martinez-Inchausti, its deputy director of food policy, added: “Food-to-go retailers that provide takeaway products proactively provide energy information for their products and have further nutrition information available whilst all major supermarkets have led the way in providing clear labelling using the UK recommended front-of-pack scheme.”

    Costa told the BBC that the figure of 40.3g of sugar for its blueberry muffins is not correct. It said this figure appeared on its nutritional information as a result of an internal error. The sugar content was previously 33.4g per muffin, Costa said.


    NHS recommended sugar limits guidelines

    • Children aged four to six: Five teaspoons of sugar per day
    • Children seven to 10: Six teaspoons
    • Adults: Seven teaspoons View comments

A blueberry muffin ‘could have day’s worth of sugar’

Some blueberry muffins sold by cafes and supermarkets contain more than the recommended daily intake of sugar for adults, researchers have discovered.

An analysis by Action on Sugar and the Obesity Health Alliance in January found the cakes could contain up to eight teaspoons of sugar.

The recommended daily limit for adults is seven – for children it is less.

Health experts said the findings showed it was “all too easy” to consume “huge” amounts of sugar.

  • ‘Limit children’s snacks to 100 calories’
  • Kids devouring ‘breakfast sugar’

    ‘Limited labelling’

    Action on Sugar and the Obesity Health Alliance, which looked at 28 muffins sold in food outlets in train stations and supermarkets, found 61% of them contained six teaspoons of sugar or more – the upper daily limit for a child aged seven-to-10 years old.

    They also found muffins bought at train station food retailers had 19% more sugar per portion and were 32% bigger than those bought in supermarkets.

    There was also a big variation, with muffins from Marks and Spencer containing just three teaspoons.

    Caroline Cerny, from the Obesity Health Alliance, said: “We may think grabbing a blueberry muffin is a reasonably healthy option for a snack on the go compared to other cakes or a chocolate bar – yet the figures suggest otherwise.

    “There is huge variation in both the size of muffins and the sugar content, and with limited nutrition labelling, it’s all too easy to eat a huge amount of sugar in just one serving.”

    The research also found a lack of nutrition labelling on a number of muffins, both those sold in stations and in supermarkets.

    The two organisations are now calling for manufacturers to reduce sugar in line with the government’s plans to cut it by 20% in common products by 2020.

    They are also calling for front-of-pack “traffic-light” nutrition labelling to be mandatory across all products, including the out-of-home sector.

    The British Retail Consortium, which represents food retailers, said its members were “actively engaged” in Public Health England’s sugar reduction strategy and had removed thousands of tonnes of sugar in products such as bakery items.

    Andrea Martinez-Inchausti, its deputy director of food policy, added: “Food-to-go retailers that provide takeaway products proactively provide energy information for their products and have further nutrition information available whilst all major supermarkets have led the way in providing clear labelling using the UK recommended front-of-pack scheme.”

    Costa told the BBC that the figure of 40.3g of sugar for its blueberry muffins is not correct. It said this figure appeared on its nutritional information as a result of an internal error. The sugar content was previously 33.4g per muffin, Costa said.


    NHS recommended sugar limits guidelines

    • Children aged four to six: Five teaspoons of sugar per day
    • Children seven to 10: Six teaspoons
    • Adults: Seven teaspoons View comments

Millennials ‘set to be fattest generation’

UK millennials are on track to be the most overweight generation since records began, health experts say.

Based on population trends, more than seven in every 10 people born between the early 1980s and mid-90s will be too fat by the time they reach middle age.

In comparison, about half of the “baby boomer” generation, born just after World War Two, were fat at that age.

Being fat as an adult is linked to 13 different types of cancer, says Cancer Research UK, who did the analysis.

The list includes breast, bowel and kidney cancer, but only 15% of people in the UK are aware of the link, according to the charity.

Child and teen obesity spreading across the globe

UK most overweight country in Western Europe

Many unaware of eating disorder signs

Teenager challenges 100-calorie snack advert

‘Generation fat?’

Britain is the most obese nation in Western Europe, with rates rising faster than in any other developed nation.

Obesity prevalence has been increasing in the UK, from 15% in 1993 to 27% in 2015.

In 2015, the highest obesity levels were seen in people aged 55 to 64, but experts are concerned that younger generations are on track to become fatter still.

Cancer Research UK wants to make the associated health risks clear to the wider public.

Spokeswoman Prof Linda Bauld said: “Extra body fat doesn’t just sit there; it sends messages around the body that can cause damage to cells.

“This damage can build up over time and increase the risk of cancer in the same way that damage from smoking causes cancer.

“While these estimates sound bleak, we can stop them becoming a reality.

“Millennials are known for following seemingly healthy food trends, but nothing beats a balanced diet.

“Eating plenty of fruit, vegetables and other fibre filled foods like whole grains, and cutting down on junk food is the best way to keep a healthy weight.”

Prof Russell Viner, from the Royal College of Paediatrics and Child Health, said: “There is a danger that being overweight is becoming normalised, as we know that many people struggle to recognise obesity in themselves, and often are unable to see when their child is overweight.

“Knowledge of the links between cancer and smoking have driven smoking rates down dramatically amongst our young people.

“We need the same recognition of the dangers of obesity.”