BMI Calculators – Are They Useful?

Seunga (Jasmine) Han, PharmD Candidate

Obesity

Obesity is a common, serious, chronic condition affecting both children and adults worldwide. In fact, about 40% of the adults in the United States were obese in 2016,¹ while about 20% of the adults in Canada were reported to be obese in 2014.² As our days become busier and it becomes harder to eat healthy and stay in shape, it’s more than likely these numbers may continue to grow. Typically, multiple factors contribute to unhealthy body weight, including but not limited to:³

• Genetics
• Medical conditions
• Medications
• Psychological factors
• Environmental factors

Am I Overweight?

Knowing that everyone is built differently, how do we determine who is considered clinically overweight?

Body Mass Index, also known as BMI, is the most commonly used measurement by healthcare professionals to determine an individual’s level of obesity. It’s calculated by dividing a person’s weight in kilograms by the square of their height in meters (kg/m²). These days, you can easily do this on your own using an online BMI calculator or app on your phone or computer. Based on the result of the calculation, individuals may be categorized into one of the following categories:^1,3

• BMI <18.5: underweight
• BMI 18.5 to <25: normal
• BMI 25.0 to <30: overweight
• BMI >30.0: obese
  • BMI 30 to <35: class 1 obese
  • BMI 35 to <40: class 2 obese
  • BMI 40 or higher: class 3 obese

While BMI doesn’t measure body fat directly nor is it used alone for diagnosis, research has shown that BMI does correlate with metabolic and disease outcomes. Since it’s so easy to perform, it’s quite commonly used by many as a quick and easy way to assess body weight.^1,3

Caveats with BMI Calculators

There are several exceptions to consider when using BMI as a form of measurement. First and foremost, BMI calculators are only useful in adults between the ages 20 and 65 and do not apply to infants, children, adolescents, pregnant or breastfeeding women, or anyone over 65 years of age. Furthermore, it’s important to remember that for BMI:^1,3

• Women tend to have more body fat than men 
• Individuals of African-American descent have less body fat than those of European or Anglo-Saxon ancestry
• Older people have more body fat than younger adults
• Athletes have less fat than the general population

Waist Circumference

Another important exception is that people who do weight training or muscle-resistance exercises regularly may have an overweight or obese BMI compared to those who do not. In cases like this, BMI doesn’t provide useful information on the distribution of body fat, which is important to consider as having too much fat around your waist (central body fat distribution) is associated with increased risk of diseases such as diabetes, high blood pressure and other heart conditions.

Why does central body fat affect our health so much? Remember that the majority of our major organs are located near the abdomen, and as such, having excessive fat in this area can have negative consequences. That said, we generally want to aim for a waist circumference of:

• For men: less than 40″ (102 cm) 
• For women: less than 35″ (88 cm)

You can measure your waist circumference by:^1,3

1. Standing up straight
2. Placing a measuring tape around your lower waist, just above the hip bones
3. Making sure the tape is horizontal around your waist
4. Take note of the measurement just as you breathe out

The Bottom Line

Outside of a few exceptions, BMI may be a helpful indicator of body fat and your overall health as you pursue a healthy weight and lifestyle routine. Obesity is associated with many negative health outcomes such as high blood pressure, diabetes, heart disease, bone problems, aches and pains, and even death. However, the good news is that obesity is one of the few chronic health conditions we can largely control through positive lifestyle choices.

While all of us probably know the value of following a good diet and exercising, we can’t deny the fact that it’s challenging – and not everyone can make the right changes, as much as they may want to. But remember, you don’t have to do it alone (nor should you). It can be as easy as reaching out to a healthcare provider, dietician, or personal trainer for advice, or simply asking a friend to be your workout buddy. Involving others can make a huge difference in achieving your goal.

As always, we hope you took away something valuable from this piece. If you have any questions or concerns regarding this article or others, feel free to reach out to us on Instagram, Facebook, or at ask@orbishealth.ca with your feedback. We’d love to hear from you.

RESOURCES

1. Centers for Disease Control and Prevention
2. Statistics Canada
3. RxTx