'Waist size as important as BMI in defining obesity'

Waist size could offer a better indication of a woman’s overall health and risk of obesity-related illness than body mass index (BMI), new research has suggested.

Women who believe they are a healthy weight because their BMI is within the normal range could unwittingly be at higher risk of premature death because of their waist size.

Current guidelines state that doctors only need to take patients’ BMI into consideration when assessing the risk of obesity-related health issues.

But researchers believe more attention should be paid to the excess body weight stored around the middle of the body, known as central fat.

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The study, by a team at the University of Iowa and published in the Journal of the American Medical Association, tracked the health of more than 156,000 post-menopausal women between the ages of 50 and 79 from 1993 to 2017.

They found that those with a BMI reading of less than 25 but a waist circumference of 35 inches or greater were at a 31 per cent higher risk of dying during the study period than women of a normal weigh and a waist of less than 35 inches.

BMI is defined as a person’s total mass divided by the square of their height.

In the UK, a score of 18.5 to 24.9 is considered healthy, 25 to 29.9 overweight, and 30 and above obese.

However, the score does not take into account the type or location of fat, which researchers can play a role in the risk of developing serious illnesses such as heart disease or cancer.

Commenting on the findings Wei Bao, professor of epidemiology in the UI College of Public Health and the study’s lead author, 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.

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Researchers suggested guidelines could perhaps be updated to consider waist size as well as BMI.

“People with normal weight based on BMI, regardless of their central obesity, were generally considered normal in clinical practice according to current guidelines,” he explained.

“This could lead to a missed opportunity for risk evaluation and intervention programmes in this high-risk subgroup.”

The authors did cite several limitations in their study, including the fact that they only analysed older post-menopausal women, and had to rely on waist circumference as they did not have imaging data of the fat.

Earlier this month it was revealed that obesity has overtaken smoking as a risk factor for some types of cancer – including four of the most common.

In cases of bowel, kidney, ovarian and liver cancer, obesity is a bigger risk factor than cigarettes, according to the latest research from Cancer Research UK.

Obesity is thought to affect around one in every four adults in the UK, and roughly one in five children aged 10 to 11.

Earlier this year, a debate broke out over whether obesity should be labelled as a disease or a lifestyle choice, after the Royal College of Physicians called for obesity to be reclassified as a the latter.