The Body Mass Index (BMI) is a metric used to assess obesity in large numbers of people. It’s a great statistics tool, offering insights on how many people in a large group have weight problems. But it’s not the right one to evaluate the risks to one’s health, new study shows. Instead, professionals should focus on body fat levels.
BMI is a deceptive metric
The Body Mass Index does not give people clear indication of the fat content of their body. It simply measures the relation between an individual’s height and weight, and decides whether said individual is overweight or not. The BMI doesn’t reflect the individual’s body composition – it’s just a crude measure that’s not a good indicator of health.
Someone with a high muscle mass can have a high BMI, well in the overweight category.
“It’s important to be attuned to what you are made of, rather than just how much you weight,” researcher Dr. William Leslie told the press. The relationship between body size and health is too “nuanced” to be explained by a simple indicator, like BMI.
Body fat can indicate risk of early death
In a recent study published in the Annals of Internal Medicine, doctors from the Universities of Alberta and Manitoba have taken a look at the associations of BMI and body fat percentage and mortality. They found that people with more body fat – regardless of their size – are at higher risk of dying early than people who have less fat.
The study authors have possibly found an answer to the so-called “obesity paradox”, a pattern seen in various studies: overweight and moderately obese people with heart issues or other health problems outlive their thinner counterparts. The studies in question have often relied on BMI, which could explain why their results are off.
The cohort analysis took a better look at 55,000 participants, most of them women with a median age of 63.5 years, BMI of 27 and mean body fat of 32.1%, and men with a median age of 65.5 years, BMI of 27.4 and mean body fat of 29.5%. The results of the study show that BMI was not the correct indicator to assess the participants’ risk of premature death. High body fat percentage, in turn, was found to be associated with increased mortality.
Men and women with the highest body fat percentage were more likely to die early than those with a BMI of over 25. Participants with a BMI over 25 were actually less likely to die early than those in the “normal” weight range. Given the age groups, the study focused on, the lower BMI can reflect bone frailty or waning of the muscles, not necessarily a lower body fat percentage.
In our society there’s been this mantra that thin is ‘in,’ and being heavy is ‘bad.’ But health is about more than the number on your scale.
Dr. William Leslie
Being active and eating healthy might not lower your body mass index, but they can help you with your body fat percentage – and keep you among us for longer.