There is no perfect number for a "healthy weight" for all people. Everyone is different, and the right weight will be different depending on the person," fitness trainer and coach Arabella Featherstone declares. 

Medicine uses figures to assess health and measure risks, and the BMI (Body Mass Index) is one of those figures. But for these numbers to make sense, they must be inclusive.

Simply put, the BMI is a measurement that uses weight and height to classify an individual as underweight, normal weight, overweight, or obese. Clinicians use BMI to assess a patient's risk for diseases. 

However, the integrity of BMI in predicting an individual's state of health is on trial. What are the limitations of BMI, and how should we use BMI? 

What does BMI mean?

BMI is a standard metric for measuring overall wellness via weight status. 

To calculate your BMI at home, measure your height and weight using a scale and use one of the formulas below to get your BMI:

Metric units: weight (kilogram) divided by height squared (meters)

• BMI = kg/m2

Imperial units: weight (pounds) divided by height squared (inches) multiplied by 703

• BMI = 703 (lbs/in2)

Alternatively, you can use a BMI calculator, like the one provided by the National Institutes of Health (NIH). Once you calculate your BMI, you can compare the figure with the standard in the scale below to know where you fall. 

In fairness to Lambert Adolphe Jacques Quetelet, the mathematician who developed BMI, he used it as a tool for population studies. That is, the numbers may not be ideal for individuals.

The medical community frequently uses it to mirror a patient's health status, but concerns are growing about its reliability and suitability. 

Should we still rely on BMI? Experts weigh in.

BMI puts the normal weight between 18.5 to 24.9kg/m2. That means any figure above or below this range is "abnormal." In fairness to BMI, several studies conclude that people with a BMI that falls outside this normal range have an increased risk of certain diseases. 

An article by the NIH identifies some health risks of being overweight and obese as 

• heart disease
• stroke
• diabetes
• sleep apnea
• kidney diseases 
• and more. 

These are some of the most common chronic conditions, so the attention that BMI gets is understandable. And most times, BMI measurement is a routine check in the hospital. 

But is BMI worth the hype? 

Experts don't think so.

Experts Identify some limitations.

• It doesn't factor in other things that contribute to health.

"The number does not tell the full story about a person's presence or absence of disease, nor does it actually tell the story of a person's health," says Wendy Schofer, a pediatrician and weight coach. 

Schofer encourages her patients and community clients to see health as a dynamic, ongoing process. She focuses on the history and functional assessment instead of the BMI.

"We all have health, not defined by a number or an action. We have health at all sizes and body shapes," Schofer explains. 

Michael Green, a board-certified obstetrician-gynecologist with the Northridge Medical Center, expresses a similar opinion. Green believes that BMI falls short of addressing every individual's unique makeup. 

For instance, men have more muscle mass and less fat mass than women, but BMI uses the same scale for both genders. Similarly, BMI doesn't factor in that muscle mass declines with age while fat mass increases. And scientists believe that a higher BMI protects older adults against diseases. 

• It doesn't differentiate between types of body mass.

Body mass includes muscle, fat, water, and mineral. And the most important health risk determiner is fat mass. Unfortunately, the BMI doesn't directly calculate the percentage of fat. 

So athletes or people with a higher muscle mass having low body fat may be wrongly categorized on the scale. So a bodybuilder who looks huge may weigh the same as another person who doesn't build muscle but has more fat. 

• It gives no information about body fat location.

BMI assumes excess fat deposition in any area of the body portends danger. However, that's flawed. In the real sense, fat deposits in the upper regions of the body, like the stomach, are the real concern. 

Those who store fat in the lower areas are less likely to be at risk of chronic diseases.

Healthline says fat accumulating in the abdominal cavity, visceral fat, is dangerous. 

Essentially, not all fat is dangerous as BMI wants us to believe. 

• It disregards race

Quetelet used a sample of White European men for his calculation. However, these cut-off points are accepted globally, neglecting our different body compositions and changing demographics.

But the World Health Organization (WHO) has since adjusted the scale for people of Asia due to more incidences of obesity at lower BMI. But that doesn't solve the problem since individual differences still exist. Moreover, these alterations do not mirror the realities of other races. 

While we can't ignore BMI, a unique scale for each race may be more beneficial to stem the incidences of misdiagnosis. 

How should we use BMI?

Schofer argues BMI doesn't contribute to the assessment of health at all. She contends that focusing on risk isn't helping individuals struggling with their weight. 

"And we tend to overly focus on risk instead of looking at an individual's health status. The last thing my patients and clients with higher BMI want to hear about is their risk of diseases," she concludes. 

However, Tara Scott, MD, believes BMI can be a starting point to assess clinical disease risk.

Like other health measures, BMI cannot be used as a single health measure. Instead, it gives more information about the future than the current state of health. 

Conclusion

We can't trash BMI, but we can alter our approach. 

Knowing your BMI is as important as knowing its limitations. And health professionals should apply more caution when counseling people because there is no perfect number for a healthy weight for all people. 

Sources:

Ana Gotter. (2021). Visceral fat. https://www.healthline.com/health/visceral-fat

Connor B, et al. (2022). BMI classification percentile and cut off points. https://www.ncbi.nlm.nih.gov/books/NBK541070/

National Institutes of Health. https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm

National Institute of Diabetes and Digestive and Kidney Disease. (2017). Health risks of overweight and obesity. https://www.niddk.nih.gov/health-information/weight-management/adult-overweight-obesity/health-risks

Thank you for reading Patient Education Essentials, the Write Shift RN blog.

Disclaimer: This article was written as a guest post for Write Shift RN LLC's blog. The information in it may not be wholly fact-checked or edited, allowing the reader to see the writer's work and skills firsthand. This information is not intended as medical advice. It is for informational and educational purposes only. Always talk to your doctor or other qualified healthcare providers about any questions or concerns you may have regarding medical conditions.