BMI: What’s Your Number?

Michelle Regan
September 05, 2018

Sometimes it seems like there’s a number for everything. What’s your weight? What about your body mass index? Your body fat percentage? Your waist-to-hip ratio? It’s tempting to want to boil your health down to a few simple digits. But what do these numbers mean and are they good indicators of health?

Let’s start with BMI.                                      

What is BMI?
BMI stands for body mass index. It’s a body fat calculation based on your height and weight. You can calculate your BMI using an online calculator or chart. Then, check your results:

What’s good about BMI?
It’s a simple calculation that doesn’t require a lot of skill or expensive tests to determine. “BMI is used because it’s easy to measure and reliable, “says Andrew Perry, MD, FAAP, FACEP. “In the majority of patients, it’s correlated with body fat percentage and body fat mass and it’s better than using body weight alone.” 

What’s not?
BMI is a 200-year-old calculation that doesn’t always calculate body composition accurately.  Perry says it’s common for athletes with a lot of muscle mass and little body fat to have a high BMI because the calculation only takes height and weight into account. Kupuna may also see faulty results because we lose muscle mass as we age.

“BMI is not a good measurement of anything,” says Tim Rabetoy, certified personal trainer and medical exercise specialist. “You can have a BMI that qualifies as overweight or obese even though you’re in great shape. On the flip side, many people with so-called healthy BMIs have too-high blood pressure or cholesterol, inflammation, or insulin resistance. Those are all truer tests of your wellness.”

The verdict:
BMI is easy to calculate if you know your height and weight. It can be a fairly accurate indicator of obesity in adults. But BMI doesn’t tell us much about body composition and could give some people, like athletes and the elderly, false results. Your BMI is worth knowing but you shouldn’t rely on it as a sole indicator of health.

What’s Your Number? is a new series that explores health measurements and what they mean. Look for more posts coming soon.

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