Body Mass Index or BMI is a widely used test to determine if you’re overweight or obese. But how accurate is it? Our Healthy Skeptic investigates.
VIDEO TRANSCRIPT
The Claim: Body mass index (BMI) is a good indicator of whether you’re overweight or obese.
Man: “The last time had a BMI test it told me that I was overweight and I was working out at that point my life so I wasn’t quite sure why that was the result I got.”
Robert Davis: Body mass index or BMI is a widely used tool at health clubs and other places to identify who’s too skinny, who’s too heavy, and who’s just right.
Developed nearly two centuries ago, this mathematical formula was intended to study weight in large populations, not to assess individuals.
But that’s how it’s often used today, and the results sometimes carry more weight than they should.
BMI is based on just two measurements: height and weight.
A reading below 18.5 means you’re underweight; 18.5 to 24.9 normal; 25 to 29.9 overweight; and 30 and higher obese.
A major advantage is that it’s simple… but often too simple.
For example BMI doesn’t distinguish between muscle and fat, so someone who’s muscular and athletic may have a high BMI even though their body fat is low.
Conversely, someone who’s frail or inactive, with low muscle mass but a relatively large amount of fat, may fall in the normal range.
Another drawback: BMI doesn’t measure where fat is located, which is important.
People who carry extra weight around the waist are at greater risk of diabetes, heart disease and other health problems than those whose fat is concentrated around the hips, thighs or buttocks.
What’s more, BMI doesn’t take into account ethnicity, age or gender, all of which influence the relationship between weight and health risk.
So does fitness. Regular exercise can reduce the health risks associated with being overweight or obese. But BMI doesn’t measure this either.
One alternative to BMI is measuring waist size.
Anything above 35 inches in women and 40 inches in men signals an increased risk of heart disease and diabetes.
Another option: measuring your waist and dividing it by your height in inches. Your waist size should be less than half your height.
Despite the drawbacks of BMI, if you’re told that your reading is high, don’t ignore it. Ask for further assessments to confirm whether you need to lose weight, and if so, how much. By getting to a size that’s healthy for you and sticking to it, you’ll be lifting an important weight off your shoulders.
Helping you be a healthy skeptic, I’m Robert Davis.