Middle-aged women with a waist bigger than 35 inches are at risk of an early death even if they are of a ‘healthy’ weight, experts warn.
It means women with a size-18 dress fitting or above could be at risk, even if they have always been told they do not need to worry about their weight.
The research, led by the University of Iowa, casts into doubt the validity of ‘body mass index’ or ‘BMI’ – the standard measure of whether someone is of a healthy weight.
Experts stress that BMI – which measures someone’s weight against their height – does not differentiate between muscle and fat.
It also does not tell doctors where fat is accumulated in the body.Fat around the waist is dangerous because it wraps around crucial internal organs, especially compared to fat that accumulates on the thighs or face.
Professor Wei Bao, who led the new research, said: ‘The results suggest we should encourage physicians to look not only at body weight but also body shape when assessing a patient’s health risks.’
The findings are particularly alarming as the average waistline of women in England now exceeds 35 inches – putting most women into the at-risk category.
Women in England have grown an average three inches around the waist in 24 years, up from 32.2 inches in 1993 to 35.2inches in 2017, according to the most recent data gathered by NHS Digital.
In the US, women’s waistlines went up more than 2 inches between 1999 and 2015, from 36.3 inches to 38.6 inches, according to the National Center for Health Statistics.
The new research, published last night in the JAMA Network Open medical journal, involved 157,000 postmenopausal women in the US aged 50 to 79, who were tracked from 1993 to 2017.
The researchers found those who were considered of normal weight – a BMI score of 17.5 to 25 – but had a waist size of more than 88cm (34.6in) were 31 per cent more likely to die within the two-decade study period than those who had a normal weight and slim waist.
They were most likely to die of heart disease or obesity-related cancer.
Professor Bao said: ‘People with normal weight based on BMI, regardless of their central obesity, were generally considered normal in clinical practice according to current guidelines.
‘This could lead to a missed opportunity for risk evaluation and intervention programmes in this high-risk subgroup.’
Experts who were not involved in the study welcomed the findings.
Dr Katarina Kos of the University of Exeter said: ‘Fat contributing to central obesity is known as ectopic fat.
‘It is called “ectopic” for the reason that it is not at the correct place.
‘Fat stored below the skin in what is known as subcutaneous fat tissue is the preferred place to store surplus energy.
‘Unlike central fat, it makes us more likely look physically bigger and it can add considerably to BMI.
‘The authors have an important message, which is for everybody keeping up a healthy lifestyle regardless of our overall build and, not surprisingly, the cohort of lean women with little central fat were found more active.’
Dr Joy Leahy of the Royal Statistical Society, said: ‘It should be noted that women of normal weight with a high waist circumference are a relatively small subgroup – 0.9 per cent of all women in this study and 2.6 per cent of women with normal weight in this study.
‘However, it is relatively easy to measure waist circumference in addition to BMI.
‘Therefore, the results of this study provide a compelling argument for including a measurement of waist circumference in the guidelines for clinical practice for women of normal weight.’