In a study from University College Cork, scientists found waist-to-hip ratio is a stronger predictor of early death than BMI and should be considered as a superior measure of healthy weight.
Body mass index (BMI) is widely used to assess whether a person is at a healthy weight, with a BMI of 18.5-24.9 kg/m2 considered to be in the healthy weight range.
However, BMI doesn’t take into account fat distribution.
It doesn’t consider where fat is stored—whether it’s accumulated around the hips or the waist. As a result, BMI doesn’t reliably predict the risk of disease or mortality.
In the study, the team wanted to find out whether waist-to-hip ratio (WHR) or fat mass index (FMI) would more reliably predict mortality across different fat distributions.
They first investigated whether higher levels of fat actually cause increased mortality or are merely correlated with it.
They used data on UK Biobank participants who had genes known to raise the risk of weight gain/obesity (i.e. genetically-determined adiposity).
They found that higher levels of fat actually cause increased death, rather than being merely linked to it.
The researchers then applied genetically determined adiposity measures—information on the genes associated with BMI, WHR, and FMI—to data on 25,297 Caucasian men and women whose health had been tracked as part of the UK Biobank study until their death; and 25,297 matched controls from the same study.
They found the risk of early death was lowest for those with the lowest WHR and then steadily increased with increasing WHR.
In contrast, BMI and FMI had a J-shaped relationship with all-cause mortality, meaning that those with either an extremely high or low BMI or FMI had an increased risk of mortality compared to those with a moderate BMI or FMI.
WHR was more strongly linked to all-cause death than BMI or FMI.
For example, each one-unit increase in WHR increased the odds of early death by almost twice as much as a one-unit increase in BMI or FMI.
The association between WHR and all-cause death was stronger in males than females.
Unlike BMI and FMI, the link between WHR and all-cause mortality was consistent across different fat distributions.
The team says WHR better reflects levels of abdominal fat, including visceral fat, which wraps around the organs deep inside the body and raises the risk of a range of conditions, including type 2 diabetes and heart disease.
With WHR, the message is simply ‘The lower the WHR, the lower your mortality risk.’
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The study was conducted by Irfan Khan et al and presented at the annual meeting of the European Association for the Study of Diabetes (EASD).
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