What BMI May (Not) Say About Your Health


Wouldn’t it be great if there was one measurement that could just tell us we’re on the road to good health? Unfortunately, that doesn’t exist, but we do have numbers, like body mass index (BMI), that act as road signs to indicate how we’re doing. Since BMI is widely used, it’s important to understand what it does and does not tell us about our health.

Weight Versus BMI
Weight is easy enough to understand: It’s the number on your bathroom scale and what you constantly work on in order to reach your fitness goals. Weight alone doesn’t tell you very much unless you take height into account. This is where BMI comes in. BMI is a more complex measure and is the ratio between a person’s weight and height. The lower the number, the less weight a person carries for their height, and vice versa. Here’s the formula for BMI and the chart that tells you where you fall:

BMI = weight (kg) / [height (meters)]2

BMI Classification
< 18.5 Underweight
18.5–24.9 Normal or Healthy Weight
25.0–29.9 Overweight
30.0 and above Obese

Source: Centers for Disease Control and Prevention. See reference list.

The Ups and Downs of BMI
As you’d guess, falling into the “normal” classification is ideal since it minimizes your risk for getting a chronic illness as you age. Having a higher than normal BMI indicates that you have higher than normal amounts of body fat, particularly in the belly region. Belly fat is considered more dangerous than fat in other areas of your body since it’s associated with a higher risk for type 2 diabetes, heart disease and even cancer. Using BMI works well for the average person (e.g. the nonathlete), which is why we see it everywhere from the doctor’s office to your mobile-friendly calorie counter.

Sadly, BMI falls short in accurately describing body composition for some athletic individuals since it doesn’t definitively distinguish between weight from muscle versus fat. This has always been the greatest criticism against the BMI: It inaccurately categorizes these individuals as overweight or even obese. This is particularly true in athletes who tend to have a higher weight from larger amounts of muscle (think: NFL running back) and often fall into the overweight or obese BMI categories.

Additionally, BMI can also give a false sense of security to someone who has a normal BMI but is otherwise “unhealthy.” For example, someone who physically appears thin to normal weight can still have high cholesterol, high blood pressure and higher risk for chronic illness.

The bottom line is that it’s still important to know your BMI. While BMI does not tell you exactly what’s going on with your organs, blood work, mental health or emotional wellness, a good deal of research has shown a link between an overweight or obese BMI and poor health outcomes. BMI is a helpful starting point for looking at your health. It can start a conversation between you and your health care provider about whether a change in your weight is needed. It is a piece of your health story but certainly not the only one.

How Else Can I Measure “Health”?
To simply be categorized as “unhealthy” based on BMI alone is not accurate, and sometimes not fair. Instead of just focusing on weight and BMI, use them in conjunction with other measures to paint a fuller picture of your health. Here are some of the most important factors to track along with your BMI:

1. Pair your scale with your tape measure. Waist circumference is a better indicator for how much belly fat you have. Make it a goal to reduce waist circumference through exercise and healthy eating. An ideal waist circumference measurement is less than 35 inches for women and less than 40 inches for men. Check out this article if you want to know how to measure waist circumference the right way!

2. Invest in a smart scale. It’s common for someone who uses exercise for weight loss to initially lose body fat but also gain muscle. This translates into little weight loss on the bathroom scale and can feel frustrating. Rest assured it’s an awesome change for your body! You can see this phenomenon by tracking your body composition with a smart scale, which uses “bioelectrical impedance” (aka a stream of electricity that won’t hurt) to estimate your body fat percentage. While these scales aren’t 100% accurate, they help you visualize your progress over time.

3. Don’t forget your annual exam. If you haven’t seen the doc in awhile you may benefit from getting your annual physical. Improving your blood work (such as your cholesterol, blood pressure, blood glucose) won’t just make your doctor happy, it also plays a role in helping you live a longer, healthier life, too. Having normal lab values is especially important if you have a low to normal BMI but are living a sedentary lifestyle and eating a relatively unhealthful diet.

4. Celebrate your “nonscale” victories. Not everything related to your health can be measured, so remember to celebrate small victories. For example, are you able to run a mile where you couldn’t before? Are you able to play with your young ones without huffing and puffing? Are you able to finally touch your toes? These successes are what I consider the hard work of lifestyle change and are often not given enough credit.

Start with BMI, but Don’t Stop There
Knowing your BMI is definitely important. Start by calculating yours at the MyFitnessPal BMI calculator. But don’t stop there! Using other measurements apart from BMI, visiting your doctor regularly and celebrating your successes are part and parcel to living a healthier life. You can also plug into the MyFitnessPal community to start making those small, important changes that can really make a difference. You got this!

About Adult BMI. Centers for Disease Control and Prevention. Available at: Accessed on October 8, 2015.

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