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What Does the BMI Reveal? The Underweight, Overweight, Obese, and Healthy

What you don’t know can harm you.

Key points

  • A “healthy” BMI classification may not mean healthy.
  • A person can become unhealthy while trying to reach the "healthy" BMI range.
Alli Spotts-De Lazzer
Source: Alli Spotts-De Lazzer

Most of us in Western medicine systems know which category of the body mass index, the “BMI,” our body matches. Our medical providers and the printouts after each office visit often highlight it for us. Weight and BMI are usually viewed as essential, main features of overall health. But what do the BMI categories of “underweight, healthy, overweight, and obesity” accurately reveal about our health status?

A brief reminder of what the BMI is and isn’t

The BMI is a screening for body fatness that’s frequently used to identify one's risk of potential disease. The Center for Disease Control and Prevention warns: Do “not diagnose body fatness or health” of an individual by utilizing the BMI alone or as the main source. Nevertheless, many do.

Underweight

A classification of “underweight” is supposed to indicate low body fatness and is considered a health risk.

I have a friend and colleague, Staci, who has been naturally quite thin her whole life. She's done some pretty extreme eating to try and gain weight. But, like many who struggle to lose pounds, she struggles to gain them.

In a mini-memoir in MeaningFULL: 23 Life-Changing Stories of Conquering Dieting, Weight, and Body Image Issues, she shared that she was denied a particular level of insurance primarily because “My weight mattered as the thing. The underwriter said the decision-makers wanted me to gain [an unrealistic amount of weight] to be ‘healthy' enough to be insured.”

That's a lot of significance put on a person's weight status—and pressure put on a person about it, too. Could factors other than weight affect someone’s current and future health? What about laboratory tests? Energy level? Overall lifestyle, sleep patterns, mental health, genetics, physical activity, social connectedness, receiving adequate nutrition?

Healthy

“Healthy” is supposed to indicate that your weight is in a healthy range for you.

Have you ever met or known anyone in the “healthy” BMI range who has been diagnosed with high blood pressure, type-2 diabetes, or high cholesterol? What about a stroke, heart disease, or gallbladder disease? These medical conditions are often linked to higher weight BMI categories. Yet, people in the “healthy” weight range experience them, too. The “healthy” weight range does not mean safe from these diseases.

Further, some people try over and over to lose enough weight to make it into the “healthy” weight category. Instead, they lose and gain repeatedly. Some even develop eating disorders. Weight cycling and eating disorders are not healthy.

Overweight and obese

“Overweight” and “obese” are supposed to indicate high body fat and an increased risk for various diseases, such as those already named and more. Yet, people in these categories may not experience those conditions, ever. People who are overweight can be healthy and well. Further, a meta-analysis by Flagel and colleagues revealed that people in the overweight range had been shown to live longer than any other weight category.

What you don’t know can harm you

Alli Spotts-De Lazzer
Source: Alli Spotts-De Lazzer

Research by Tomiyama and colleagues shows that the BMI “ignores overweight and obese individuals who are cardiometabolically healthy.” For example, the BMI’s classifications labeled 54 million Americans as unhealthy when they weren’t. And, another 21 million Americans were assessed as “healthy” in terms of BMI, but when evaluated further, they weren’t. The instrument’s fallibility makes sense since the BMI was created around 200 years ago.

Today, various providers regard the BMI as outdated, too general, or potentially misleading. The math formula includes only weight and height. It doesn’t take into account other critical individual factors (musculature, bone density, age, ethnicity). At their fittest, an elite athlete can land in the “obese” category.

There’s a movement towards weight-neutral management of health. In a nutshell, weight-neutral doesn't concentrate on BMI, weight, or weight loss. Instead, lifestyle behaviors are primary—those that enhance health and quality of life outside of a weight focus.

I ask you

  • If you exclude anything weight-related, what will you work on to live a healthier life?

For example, do you want to increase your strength? Up your cardiovascular endurance or simply move your body more? Add more pleasure to your life? Learn to relax? See a doctor for a physical exam and overdue laboratory work? Sleep better?

Think about what might constitute your healthier life. Non-weight-focused changes are usually more sustainable than weight-focused ones.

Overvaluing weight loss or that "healthy" BMI range can frustrate, and efforts to change weight can prove futile. Many people’s genetics, metabolism, or socioeconomic status won’t let them keep weight off (if it comes off in the first place). Furthermore, science repeatedly demonstrates that most diets fail. You don’t fail at dieting; dieting fails you. And feeling like a failure is probably not going to contribute positively to your health either.

If you’re seeking wellness, maybe try this experiment. Remember that question I posed earlier—the one under the “I ask you” heading? Test out your answer. The results can benefit your physical and mental health.

This post is for informational purposes only and does not provide therapy or professional advice.

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