Slim-looking people at risk of heart attack and stroke, study finds

Hidden fat surrounding organs and stored in the liver may quietly damage arteries – even in people who look thin – according to a major study.

Researchers at McMaster University in Canada analysed MRI scans and health data from more than 33,000 adults in Canada and the UK.

They found that visceral fat – the type that builds up in and around internal organs – was strongly linked to thickening and clogging of the carotid arteries, which supply blood to the brain.

Narrowing of these arteries is a major risk factor for stroke – and may also indicate that other vital blood vessels, such as those supplying the heart, are becoming blocked.

The findings, published in Communications Medicine, challenge the long-standing reliance on body-mass index (BMI) as a measure of obesity.

‘This study shows that even after accounting for traditional cardiovascular risk factors like cholesterol and blood pressure, visceral and liver fat still contribute to artery damage,’ said co-lead author Professor Russell de Souza, from McMaster’s Department of Health Research Methods, Evidence and Impact.

He described the results as ‘a wake-up call for clinicians and the public alike.’

Co-lead author Professor Marie Pigeyre, of McMaster’s Department of Medicine, said the research highlights the need for more advanced ways to assess fat distribution – not just overall weight or waist size.

‘You can’t always tell by looking at someone whether they have visceral or liver fat,’ added Professor Sonia Anand, corresponding author and vascular medicine specialist at Hamilton Health Sciences. 

‘This kind of fat is metabolically active and dangerous – it’s linked to inflammation and artery damage even in people who aren’t visibly overweight.’

Experts say the results underline the importance of imaging-based methods to spot ‘hidden’ fat deposits that raise heart-disease risk, and could lead to more personalised prevention strategies.

The news comes as up to 60 per cent more adults could be classed as obese under a radical shake-up of the BMI system proposed by experts.

Under current rules, a BMI score of 18.5 to 25 is healthy, 25 to 29 is overweight and 30 or above counts as obese – the point at which the risk of serious illness soars.

But 58 international specialists this week suggested an overhaul of how obesity is diagnosed, arguing that BMI alone is too blunt a tool. 

They suggest adding waist size and weight-to-height ratio to give a fuller picture of unhealthy body fat.

Researchers from Harvard University and Massachusetts General Hospital, who examined data from more than 300,000 American adults, found that adopting the new definition would expand the number of people classed as obese by almost 60 per cent.

In Britain, where about 13 million adults are currently obese, the same calculation could see that figure soar to nearly 21 million.

Experts called the findings ‘important’ and warned the ‘substantial rise in obesity prevalence’ could have ‘profound financial and public-health implications’.

Under the proposed rules, people could also be deemed obese if they had a BMI below 30 but at least two raised measures, such as a waste circumference of more than 37ins for men and 31.5ins for women, or a raised waist to height ratio. 

Writing in JAMA Network Open, the Harvard team said: ‘The prevalence of obesity increased by 60 per cent when using the new definition compared with the traditional BMI-based one.’

Although their BMI appeared healthy, these so-called ‘anthropometric-obesity’ individuals had a significantly higher risk of organ dysfunction and diabetes than people without obesity – and were more than three times as likely to suffer organ damage.

The researchers also found that nearly 80 per cent of participants aged 70 or over were classed as obese under the new criteria – double the current rate.

Earlier this year, 50 experts from around the world proposed a ‘radical overhaul’ of how obesity is diagnosed and treated by including waist and height measures alongside BMI. Their recommendations were endorsed by the Royal College of Physicians.

A raft of long-awaited anti-obesity laws came into force this month.

‘Buy one, get one free’ offers on sweets, crisps, sugary drinks and other snacks have been banned in England, along with free refills of fizzy drinks in restaurants and cafés. From January, there will also be a ban on online adverts for junk food and restrictions on TV advertising before 9 pm.

Ministers say the crackdown is designed to tackle Britain’s growing obesity crisis – with excess weight linked to at least 13 types of cancer and blamed for a 39 per cent rise in type 2 diabetes among under-40s.