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'Waist size is a forgotten factor in defining obesity'

By Nina Massey, PA Science Correspondent

Women who are considered to be normal weight as measured by body mass index (BMI) could actually be at high risk for death because of their waist size, a new study suggests.

The research indicates that some people thought to be a normal weight could unknowingly be at high risk for obesity-related health issues.

Scientists say that according to current clinical guidelines, doctors need rely only on BMI to determine obesity-related health risk.

They argue this leaves people who are actually in a high-risk group because of other risk factors, like percentage of body fat, thinking they're healthy.

Wei Bao, professor of epidemiology in the UI College of Public Health and the study's corresponding 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."

The study, published in the Journal of the American Medical Association's JAMA Network Open, used data from the Women's Health Initiative.

The American study tracked the health of more than 156,000 post-menopausal women between the ages of 50 and 79 from 1993 to 2017.

Professor Bao and his team linked mortality rates to the respondents' BMI as well as their central obesity, which is the excess accumulation of fat around a person's midsection.

Women who were considered normal weight on the BMI scale but had a high waist circumference were found to be 31% more likely to die within the two-decade observation period, when compared to women with normal weight and no central obesity

That is comparable to the 30% increased likelihood those considered to be in the highest risk group - an obese person with central obesity - will within 20 years of observation.

The study found that the two primary causes of death in people who had normal BMI but high waist size were cardiovascular disease and obesity-related cancer.

Prof 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."

The researchers acknowledge several limitations in their study, including that they only looked at older post-menopausal women, and had to rely on waist circumference as they did not have imaging data of the adipose tissue - fat.