A large US study has found that being overweight but not obese carried a slightly lower risk of dying within the study period than being a supposedly healthy weight
By Clare Wilson
5 July 2023
A body mass index classed as overweight may not indicate that someone is unhealthy
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Being “overweight” may not be so bad for your health after all. The latest evidence comes from a large study where people who were classed as overweight, but not obese, had a slightly lower rate of death than people with a supposedly ideal weight – hinting that the threshold at which individuals are classed as overweight has been set too low.
It is uncontroversial that being very heavy is bad for people’s health, but it is unclear at what point health risks begin. Doctors usually advise people to lose weight if they have a high body mass index (BMI), which is someone’s weight in kilograms divided by the square of their height in metres.
In most countries, a healthy weight is defined as a BMI between 18.5 and 24.9. Having a BMI between 25 and 29.9 is classed as overweight and 30 and above is obese. These thresholds became the medical orthodoxy after being cited in a report from the World Health Organization in 1997.
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Previous research made waves when it found that people who are somewhat over the “healthy” threshold of 25 may actually have a slightly lower rate of death than those who are slimmer. But many of these studies are fairly old, done when people were generally slimmer and their participants weren’t ethnically diverse, says Aayush Visaria at Rutgers Institute for Health in New Brunswick, New Jersey.
To address those issues, he and Soko Setoguchi, also at Rutgers Institute for Health, analysed data from a more recent study, which began in 1999, and tracked the survival of about 500,000 ethnically diverse US adults of known height and weight, for up to 20 years.
Having a BMI between 25 and 27.4 carried a 5 per cent lower risk of death in this time period than a BMI within the healthy weight category of 22.5 to 24.9. A slightly higher BMI, of 27.5 to 29.9, seemed even better, linked with a 7 per cent lower risk of death.