IS YOUR BMI MISLEADING YOU? NEW STUDY SAYS IT MISSES WHO IS REALLY AT RISK
If you have ever felt your BMI did not reflect how healthy you actually feel, new research suggests you may have a point.
A study of almost 7,000 middle-aged adults in the UK has found that body mass index on its own can miss who is genuinely at risk from carrying extra weight.
The research, from University College London, UCLH and Barts Health NHS Trust, was published in the International Journal of Obesity and reported by News-Medical on November 12.
Why BMI only tells part of the story
BMI is a simple calculation based on your weight and height.
It is quick and cheap, which is why it has been used for decades, but it cannot tell the difference between muscle and fat or show where that fat sits.
It also says nothing about whether your weight is actually affecting your health.
That is why a Lancet commission proposed a new way of diagnosing obesity, designed to move beyond BMI alone.
The new approach
Under the new framework, people are placed into one of three groups.
The first is no obesity, meaning no excess body fat.
The second is preclinical obesity, where someone carries excess body fat but has no related organ problems and no difficulty with everyday activities.
The third is clinical obesity, where excess body fat comes with problems in how the body's organs work, limits on daily activities, or both.
In other words, it looks at what your body fat is actually doing to your health, not just the number on the scales.
What the BMI study found
The researchers used data from the 1970 British Cohort Study, a nationally representative group of people born in 1970 and followed throughout their lives.
They looked at 6,978 people at around age 46, including 3,635 women, using body composition, waist measurements, health reports and physical function tests.
Under standard BMI categories, 32.4 per cent were classed as having obesity and 37.8 per cent as overweight.
Under the new framework, 17.7 per cent had clinical obesity, 52.5 per cent had preclinical obesity and 29.8 per cent had no obesity.
Strikingly, only about 31 per cent of people with a BMI in the obesity range met the criteria for clinical obesity.
Meanwhile, 16.6 per cent of those in the overweight BMI range did have clinical obesity, meaning they could easily be overlooked.
When the team looked at deaths over the following five years, clinical obesity was linked to higher odds of dying compared with no obesity.
BMI categories of overweight and obesity showed no statistically significant link.
Agreement between the two systems was stronger among women than among men.
A note of caution
The researchers are careful to say this is an early finding.
Only 27 people in the group died during the follow-up period, which limits how firmly conclusions can be drawn.
The criteria still need testing across different ages, sexes and ethnic backgrounds.
As the authors put it, further research "must establish whether the criteria improve long-term risk prediction".
You can read the full study here.
What it means for you
If your BMI sits in the overweight or obesity range, it does not automatically mean you are unwell.
Equally, a BMI in the healthy or overweight range is not a guarantee that all is well inside.
The study is a reminder that health is about far more than one number.
Next time you see your GP, it may be worth asking about other measures, such as your waist measurement, blood pressure, blood sugar and cholesterol.
It is also worth mentioning if your weight is affecting your energy, joints, sleep or ability to get through the day.
Those everyday clues are exactly what the new approach takes into account.
Regular movement you enjoy, plenty of plants on your plate and good sleep all support your health, whatever your BMI.
And if you are worried about your weight or health, speak to your GP, who can look at the bigger picture with you.
