Health / Weight Loss

How Much Does BMI Really Matter?

The truth behind the numbers.

It’s hard trying to maintain a healthy, fit lifestyle. Sometimes, all the numbers that come along with it can make it even harder. How many reps can you do? Are you running that 5k fast enough? How many calories do you need? How many steps did you get in? But, one number often seems to stand out above the rest as the “defining” factor of health: your BMI.

You’ve likely heard it tossed around a lot—this BMI is too high, this one is too low, and this one is just right. But, at the end of the day, does your BMI really matter? Or is it just another number to keep track of? We chatted with some Aaptiv experts and a dietitian to get to the bottom of it.

What is BMI?

We probably don’t have to tell you that BMI is short for body mass index. But if given a fitness pop quiz right now, would you know exactly what that even means? It’s actually not as complicated as it sounds.

Simply put, it’s just a number calculated using your body weight and height. Aaptiv trainer Kelly Chase explains that this BMI number is a preliminary measurement used to distinguish if someone is underweight, normal, overweight, or obese.

As far as determining one’s BMI, that’s done by taking your weight in pounds and dividing it by your height in inches squared (i.e. your height in inches multiplied by your height in inches) and then multiplying that number by 703, according to Courtney Schuchmann, MS, RD, LDN, from the University of Chicago Medical Center.

Of course, if the above brought back flashbacks of the SAT math section, Schuchmann says that there are plenty of websites you can use to quickly input your information sans algebra flashbacks.

The BMI Issue

Sounds simple, right? A single number to tell you if your weight is healthy or not! But, hold up; here’s where things get tricky. When it comes to assessing one’s health, there are a few more factors at play than just height and weight.

“BMI used to be a predictor of health but has been controversial in accuracy. [This is] due to the fact that it doesn’t take into account a person’s body fat percentage—lean muscle mass v. fat mass,” explains Jennifer Giamo, Aaptiv trainer and founder of Trainers in Transit.

Basically, your BMI number doesn’t distinguish between muscle and fat. We all know both play very different roles in the body. Giamo also adds that age, gender, and ethnicity are also all possible predictors of health that are not factored into the BMI equation.

See the problem?

Should I stress if my BMI is too high—or too low?

To put it simply: You can be totally healthy with a higher BMI. Conversely, you can be unhealthy with an average or lower BMI.

Schuchmann explains that those with more muscle mass, think athletes and bodybuilders, will have a higher BMI. “Muscle weighs more than fat. Therefore, someone with a lot of muscle is going to have a higher BMI,” she says. She also says ultimately it comes back to someone’s diet quality and level of physical activity. “Someone that is overweight by BMI standards, but also exercises daily and eats a seemingly healthy, well-rounded diet can still be healthier than someone with a normal weight who eats primarily junk food and does not take part in any physical activity,” she adds.

And just because a BMI is lower, doesn’t necessarily mean that it equates to being healthy either. “If you have a low BMI, this can mean that you’re malnourished or under eating, which means potential health risks are involved,” explains Chase. “Anorexia, bulimia, hyperthyroidism, and gastrointestinal issues, to name a few, could lead to a low BMI.”

What’s more, those with a normal BMI may not be in the “healthy” zone either. According to Giamo, BMI doesn’t take into account those who are of normal weight, yet may carry fat in particularly dangerous places. “They may seem perfectly healthy when instead, they’re at higher risk of heart disease, diabetes, and premature death,” she says.

But, that’s not all. Schuchmann says that there are some people who just naturally have a lower BMI. Those who are considered petite and even those of Asian descent may have a lower BMI inherently. In this case, she says a dietitian can determine if an underweight BMI indicates malnutrition or is simply normal for an individual by doing a physical assessment.

Does it matter?

All of the experts we chatted with agree that the BMI system has its flaws for sure. There are so many more factors that go into someone’s health. A number calculated by height and weight simply can’t be used as the deciding factor as to “healthy” or “unhealthy.”

You need to look at indicators such as family history and genetics when determining your overall “health” status. However, you also need to look at lifestyle. Smoking, dietary, and exercise habits also all play big roles.

Bottom line, if you’re looking to maintain a healthy lifestyle—regardless of your BMI—you can start with step one: working out and eating healthy! Download the Aaptiv app today to see all the on demand fitness classes you can start taking.

“Working with a fitness professional can help you to create an exercise and nutrition plan for weight maintenance, fat loss, and improving muscle mass,” explains Giamo. And of course, we all know a healthy diet is the yin to the fitness yang. Stick to those lean meats, fruits, veggies, whole grains, nuts, seeds, and dairy daily to keep it all in check.

When assessing your health or making changes to your diet, you should always consult your doctor to see what is right for you.

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