Why BMI May Not Be the Best Metric

Woman measuring waist

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There are multiple ways to measure health, and BMI or body mass index is one method used to categorize people based on their height and weight. This measurement is often utilized to determine individuals' diagnosis, treatment, and care but has come under scrutiny as a blanket approach lacking efficacy. 

BMI was developed by mathematician Adolphe Quetelet in the early 19th century, while he was studying crime in relation to social status. During his research, he discovered a link between height and weight. In the early 1970s, physiologist Ancel Keys began using the formula to determine obesity.

Originally, BMI was specifically used for gathering large population samples of white men, but it has since been applied to individual men and women of all ages and races. 

BMI is still used today because it is an inexpensive and quick method for making assessments. According to the CDC, people with very high BMI are more likely to have high body fat percentages. However, relying on BMI creates issues with multiple population types, especially people of color. 

Defining BMI 

BMI measurements are obtained using a formula that finds the ratio of a person's height and weight. The formula uses a person's weight in kilograms divided by the square of their height in meters.

This measurement is used for classifying people into specific categories of underweight, normal weight, overweight, or obese. These categories are used to determine the likelihood of particular potential health concerns or risks. 

BMI Measurement Weight Category
Below 18.5 Underweight
18.5 – 24.9 Normal weight
25.0 – 29.9 Overweight
30.0 and above Obese

You can use this calculator to determine your BMI:

What BMI Can Reveal

While BMI is only one factor of many used to point to potential health risks, it is most often correlated with the following conditions in overweight and obese populations:

  • Coronary heart disease
  • Hypertension
  • Osteoarthritis
  • Sleep apnea and other respiratory conditions
  • Certain cancers
  • Stroke
  • Type 2 diabetes

For those with a BMI under the healthy or normal range, there are other significant potential health conditions:

  • Cardiovascular disease
  • Depression
  • Difficulty getting pregnant
  • Dry skin
  • Hair loss
  • Irregular menstrual cycles
  • Nutrient deficiencies
  • Osteoporosis
  • Reduced immune system function

Limitations of BMI

For some groups of people, it's best not to rely on BMI since it cannot provide an accurate picture of health even more significantly than the average person. These people include:

  • Muscular individuals or those who are very athletic
  • Pregnant and lactating individuals
  • The elderly
  • Children

Using the body mass index leaves out crucial information that can help determine a person's health status. For example, only using a person's height and weight leaves out the amount of body fat, bone, and muscle mass they might have.

Muscle is much more dense than fat, and therefore, individuals with a high amount of muscle mass may be heavier even with less dangerous body fat levels.

Many athletic people with a higher than average muscle mass will find themselves in the overweight range of BMI. Conversely, elderly individuals may have less muscle mass than the average, and children have not yet fully developed their bones and muscles.

Further Problems with BMI

BMI also does not consider lifestyle habits such as diet and exercise, stress levels, or other factors such as genetics, environment, or race.

Moreover, when BMI determines diagnosis and care outcomes, more issues can arise. Some people have been denied access to care for issues such as eating disorders and fertility treatments. Insurance companies often still rely on BMI when determining coverage and rates, resulting in unfair outcomes.

BMI was never designed to track individual health and, in particular, lacks effectiveness for women and people of color. Some ethnic groups have higher health risks than others, and relying on BMI to predict these health risks can leave some people out of receiving the care they may need. 

For example, Asians have been shown to have more than twice the risk of developing Type 2 diabetes than Caucasians at the same BMI. Hispanics and black people have a greater risk of diabetes than white people at the same BMI. Since BMI was developed using the data of white males, some people may be neglected when they should be receiving care.

Researchers have shown that a BMI of 30 or over is linked to a higher risk of Type 2 diabetes for white people, but for black people, 28 is a more accurate cutoff while the cutoff is 23.9 for South Asian populations and 26 for Middle Eastern people. This discrepancy could leave many at-risk individuals without proper care at critical times.

People who may file into the overweight or obese range yet are active and have healthy blood pressure, and cholesterol levels may be told they need to lose weight when they don't need to. This false determination may lead to self-image and body shaming issues and lacks a complete picture of the person's actual health status.

How to Correctly Use BMI

BMI should be part of a bigger picture when considering a person's health. Considering BMI can potentially indicate a starting place for working on improving health outcomes but should be part of a broader range of measures such as: 

  • The ratio of body fat to lean mass
  • Waist circumference
  • Neck circumference
  • Waist-to-hip ratio
  • Blood sugar levels
  • Cholesterol levels
  • Stress levels
  • Sleep habits
  • Blood pressure
  • Family medical history 
  • Diet
  • Physical activity levels
  • Habits like drinking and smoking 

If you are concerned about your BMI, speak with a health care provider while also discussing your overall health habits. Health care providers can use BMI as a jumping-off point for diving deeper into a person's health factors.

If someone has a high BMI, it could be wise to order further lab tests, particularly if they belong to a more at-risk population for medical conditions such as Type 2 diabetes. Your care provider can then determine ways to reduce your risks of these conditions, if necessary, such as diet and exercise changes.

What to Focus on Instead

Those who would like to track their body measurements would be better served using formulas and tools to provide a clearer picture of body composition. Body composition is the amount of lean mass, including muscle, bone, and organs, compared to fat mass.

Tracking body composition is especially helpful for those who are athletic or fit and tend to have a more significant muscle mass ratio than the general population. There are various methods of tracking body competition, including bioelectrical impedanceskinfold measurements, and underwater weighing

Another indicator that is more reliable than BMI regarding potential health concerns is the waist-to-hip ratio (WHR). This measurement compares your waist size to the size of your hips in inches and is often used to determine the risk of heart disease a person may have. To obtain your WHR, simply divide your waist measurement by your hip measurement in inches.

A waist-to-hip ratio greater than 1.0 indicates a higher than average risk of developing heart disease. A healthy WHR is less than 0.85 for women and 0.90 or less for men.

A Word From Verywell

While BMI may help health care providers determine whether more tests should be performed, it is not an adequate stand-alone indicator of health. Many other factors determine your health status, including your lifestyle habits, body composition, ethnicity, and genetics. If you are concerned about your BMI or your health in general, speak to your doctor. If you are at risk of health conditions, your doctor can help you develop a plan to improve your outcomes, such as diet and lifestyle changes.

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Article Sources
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