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Is BMI a load of bull$#*t?
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Take your weight and divide it by your height squared. What have you got?
If you studied health sciences at school or had a full check-up with your doctor lately, you’ve probably already twigged that this is the equation for BMI – body mass index.
For decades, it’s been the standard way to measure body fat. But experts are increasingly questioning the usefulness of BMI. With an assist from sports dietitian Angie Asche, let’s dig into the latest research to get a clearer picture of your health.
What is BMI, anyway?
The Belgian mathematician who devised the BMI in the 1830s was hoping to find the measure of the ‘average man’ – in the process, he noticed that people’s weight tended to increase in line with their height.
Whether you use metric or imperial measurements, the calculation remains largely the same (with just a little extra step to convert the imperial):
Weight (kg) ÷ [height x height] (m) = BMI
Weight (lbs) ÷ [height x height] (inches) x 703 = BMI
So for instance, if you weigh 160lbs and are 66 inches tall, your calculation would be:
(160 ÷ [66 x 66]) x 703 = 25.8 BMI
In the 1970s, this calculation was identified as an easy way to screen for obesity and its associated health risks.
Now, almost 200 years after it was first developed, BMI remains the most common way of measuring body size.
Depending on the number you get by doing the calculation above, it places you into the category of underweight (less than 18.5), healthy weight (18.5 to 24.9), overweight (25 to 29.9) or obese (30 to 34.9).
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Some people live a healthy lifestyle and have a higher-than-normal BMI.
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While it may be a popular, it is far from perfect.
Since it was developed by studying only European men, many experts believe it doesn’t account for racial and ethnic variation. For example, some studies have found that Black people tend to have higher lean muscle mass and lower body fat than white people at the same BMI.
“It doesn’t take into account body composition. In other words, it can’t tell the difference between muscle and fat,” says Angie.
“Some people live a healthy lifestyle and have a higher-than-normal BMI. Then others who have several unhealthy lifestyle factors may be classified as ‘normal’ BMI, but it doesn’t make them healthy.”
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Angie has also seen the limitations first-hand in her work with elite athletes.
“The majority of athletes have such a large amount of muscle mass that many of them are classified as overweight or even obese – even though their blood work is flawless and they’re at a healthy body fat percentage,” she points out.
“Just looking at someone’s height and weight doesn’t tell you everything about their overall health and well-being.”
Is WHR the new BMI?
In the search for a BMI replacement, a new study has put waist-to-hip ratio (WHR) at the front of the queue.
WHR estimates fat distribution in the body by dividing the circumference of your waist (measured just above your belly button) by the circumference of your hips (measured at the widest point).
This study found that WHR is a more consistent predictor of mortality than BMI. The lower your WHR, the lower your risk of death. Researchers pointed out that even with a low BMI, increased abdominal fat is unhealthy – and therefore using WHR alongside BMI, or WHR as the primary tool, may lead to better outcomes.
“WHR is a very simple way for clinicians to gather more data on their patients. When combined with several other factors such as blood work, it can help determine cardiovascular, diabetes and other potential health risks,” says Angie.
But again, she adds, waist-to-hip ratio alone doesn’t provide a full picture of your health status.
“WHR does not account for muscle mass or any other lifestyle factors. Also, it only estimates fat distribution in the waist and hips, not total body fat, which can vary tremendously between different genders and ethnicities.”
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What your BMI & WHR can’t tell you – how your mobility, stability and functional fitness is improving over time.
Bye bye, BMI: 4 better ways to measure your health
If BMI and WHR aren’t giving us the full picture, is there a better way to get an indication of our health status? Angie suggests these methods, which she regularly uses when advising clients.
1. Nutrient analysis: “Log your food intake to see what and how much you are consuming daily – from total caloric intake, carbs, fat and protein, to the macronutrients you’re getting, like fiber magnesium and vitamin D.”
2. Physical activity log: “Create a weekly log of how often you’re exercising, the type of exercise and how long you’re exercising for. Ideally it will be a mix of cardio and strength training,” Angie says. If you’re a Centr member, all of your training is logged in the app.
3. Body fat percentage test: “A body fat percentage test helps to give a better idea of the fat-free mass vs fat mass in someone’s body. This can be done via dual-energy X-ray absorptiometry (DEXA) scan or bioelectrical impedance analysis (BIA) test, which is my preference. You can also use the skinfolds method, but there’s a larger chance of error depending on the tester and their experience.” It’s important to note that these tests can be expensive and you’ll need a professional to interpret the results for you.
4. Sleep: “Sleep quality and quantity can impact several aspects of overall health. Proper sleep is the foundation of recovery and inadequate sleep leads to higher levels of cortisol and can also throw off hunger hormones.” If you’re having trouble getting quality rest, check out our series Power Sleep with Chris Hemsworth.
Disclaimer: This Centr content is adapted with permission from an article written by Lifespan.io. The content herein represents Centr’s interpretation of the original source material.
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Centr x Lifespan.io
Centr has partnered with Lifespan.io to bring you the latest in longevity research. Lifespan.io is the leading source of industry news and a nonprofit advocacy foundation whose mission is to accelerate progress toward overcoming age-related diseases. Since 2014, the organization has focused on responsible journalism, high-impact advocacy, and media initiatives that make longevity research and education more accessible to all.
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