A new study finds that checking the body mass index (BMI) should be abandoned to examine the presence of fat around the middle.
Data presented at the European Association for the Study of Diabetes in Stockholm found that waist-hip ratio is a much better predictor of premature death than looking at body mass index.
It comes after the National Institute for Health and Care Excellence (NICE) said in April that people should ensure their waist measurements are less than half their height to keep health problems at bay.
She added that adults with a body mass index (BMI) of less than 35 should measure their waist-to-height ratio as part of broader plans to tackle obesity.
A BMI of 18-25 is considered a healthy weight, 25-30 are overweight, and over 30 are obese.
By using their waist-to-height ratio, along with their body mass index, people can tell if they have excess fat around their midsection, which is known to increase the risk of type 2 diabetes, high blood pressure, and heart disease, Ness said. the heart. .
For example, a female who is 5 feet 4 inches tall and has a waist circumference of 29 inches would have a healthy ratio, but 32 inches would push her into the unhealthy range.
BMI is widely used by doctors to find out if someone is overweight.
“BMI does not take into account fat distribution,” said Irfan Khan, a medical student at University College Cork who conducted the new study with colleagues in Canada.
“It does not take into account where the fat is stored – whether it is accumulating around the hips or the waist. As a result, BMI does not reliably predict risk of disease or mortality.”
In the new study, which has not yet been peer-reviewed, the researchers first investigated whether higher levels of lipids increased the risk of death or were just related.
Using data from UK Biobank participants who have genes known to increase the risk of overweight and obesity, they found that high levels of fat actually increase the risk of early death.
Additional work on 25,297 men and women whose health was tracked as part of the study, identical to the same number of people serving as controls, showed that the association between waist-hip ratio and death from any cause increased linearly.
This means that the risk of early death was lower for those with the lowest waist-to-hip ratio, before increasing exponentially with increasing waist-to-hip ratio.
In contrast, those with a very high or very low BMI or fat mass index (another measure of fat) were more likely to die than those with a moderate BMI or fat mass index.
Waist-to-hip ratio was more associated with mortality from any causes than either BMI or fat mass index.
Mr Khan said: “The main determinant of BMI is that it does not take into account differences in fat distribution.
“This could mean that someone who has accumulated fat around their waist will have the same BMI as someone of the same age and height who stores fat around their hips, despite the health risks of belly fat.
However, the waist-hip ratio better reflects levels of belly fat, including visceral fat, which wraps around organs deep in the body and increases the risk of a range of conditions, including type 2 diabetes and heart disease.
“With the waist-hip ratio, the message is simply this: the lower the ratio, the lower the risk of death.”
Professor Nick Viner, from University College London’s Institute of Cardiovascular Sciences, said: “It has been well established that BMI is an imperfect measure of the risk of being overweight or obese, and that many (but not all) of these risks are driven not only by the amount of fat stored. in the body but where it is stored.
“It has long been known that the waist-hip ratio is more closely associated with mortality than BMI, which is why it has been included in the guidelines for the assessment and management of overweight and obesity.
“This research, using genetic methods, confirms that this relationship is causal – that is, this link is not just an association, but a higher waist-hip ratio is in fact the cause of the loss of life expectancy.
“However, there is a problem in relying on the waist-hip ratio as a measure of obesity severity, as it changes little with modest weight loss and therefore does not necessarily reflect health improvements as a result of obesity treatments that lead to weight loss.
“While mortality is of course important for many obese people, it is everyday symptoms such as joint pain, shortness of breath, mood changes and stigma that really affect quality of life and may be better related to weight rather than fat distribution.
“The findings highlight the need for better clinical measures to assess obesity and its risk, and to move away from just thinking about weight alone.”