BMI – being moderately overweight may not be as unhealthy as previously thought, claim researchers

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Being moderately overweight may not be quite as unhealthy as was once thought, according to new research published in the Journal of the American Medical Association (JAMA) - but don’t get too comfortable, warns expert.

The team of Danish researchers analysed data relating to thousands of people spanning three decades in order to investigate the relationship between body mass index and mortality. They found that, although average BMI has increased in most countries, the prevalence of cardiovascular risk factors may not be increasing as may have been expected.

The study looked at BMI and mortality rates in data samples from the general population across from three different cohorts between 1976 and 2013. The findings appear to indicate that the BMI associated with lowest all-cause mortality has increased by 3.3 over the past 30 years and, say the researchers, current advice regarding healthy BMI may potentially need adjusting over time.

Preventative medications may influence improved outcomes for obese people

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However, Professor Naveed Sattar, Professor of Metabolic Medicine at the University of Glasgow, says the findings “do not change advice we have been giving on obesity and its treatment and prevention”. He explains: “In recent years, as populations become more obese and with wider availability of cheap preventative medications many more such individuals are likely to be better treated for abnormal blood pressure, abnormal cholesterol and, if also present, type 2 diabetes, leading in turn to lower death risks.”

Being moderately overweight no protection from health problems

Professor Sattar adds: “The current findings do not mean that being overweight is protecting you from death, far from it – rather, many confounding factors may give the current result and we know from many other studies that being overweight or obese does increase mortality risks, in the same way that it increases risk for many other conditions. We also know from other studies that lower calorie intake increases life expectancy. So it’s a complex picture.

“Obesity and overweight categories also signal risks for many diseases, such as type 2 diabetes, liver disease, cancers, sleeping problems, multiple pregnancy complications, to name but a few, many of which we can manage much better these days but of course such complications also impair quality of life, impair self-esteem, and increase health costs for societies.”

Further studies required

The study authors state that the findings from the most recent cohort - 2003 – 2013 suggest that the optimal BMI in relation to mortality sits in the current overweight category. They write: "This finding was consistent in both the whole population sample (optimal BMI, 27), and in a subgroup of never-smokers without history of cardiovascular disease or cancer (optimal BMI, 26.1). If this finding is confirmed in other studies, it would indicate a need to revise the WHO categories presently used to define overweight, which are based on data from before the 1990s."

Professor Sattar says that, while modern medicines may be helping obese people live longer than they might have done in the past, BMI cut-offs relating to obesity should not be redefined as a result. He adds: “We need a holistic view on obesity and societies should make it easier for individuals to make healthier lifestyle choices.”

What is a healthy BMI?

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According to NHS Choices, a healthy adult BMI is within the 18.5 – 24.9 range. If your BMI is below this, you may be underweight.

A BMI between 25 – 29.9 is considered overweight and between 30 – 39.9 is obese. A BMI of 40 or more may indicate severe obesity.

Being overweight or obese is said to increase the risk of developing various health problems, including heart disease, high blood pressure, stroke, type 2 diabetes, some cancers and kidney disease.

Where can I check my BMI?

Visit NHS Choices to check if your BMI falls within a healthy range.

If you need to lose weight, check out our Live Healthy article.

If you have any health problems, make sure you consult your GP before embarking on any diet or weight loss programme.

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