Is BMI Not a Good Indicator of Health or Obesity?

Body mass index (BMI) is the globally accepted measure of body weight. BMI is a mathematical formula that is used to calculate weight adjusted for height. In most healthcare facilities, BMI is used as the standard assessment tool for judging a person’s overall health. For many decades now, BMI has been the preferred measurement to understand a person’s health based on body size. However, this health assessment tool is often criticized globally for being overly simple and not really indicating how healthy a person really is. Read on to find out more about whether BMI is the right indicator to diagnose obesity.

Body Mass Index, which is more commonly known as just BMI, is a measurement of a person’s weight in pounds or kilograms divided by the square of height in feet or meters. This is a measurement tool that screens for weight categories that might cause specific health problems in the future, especially related to obesity. This process is an easy and inexpensive method of screening for various weight categories, which are divided into the following:^(1, 2, 3)

• Underweight
• Healthy weight
• Overweight
• Obesity

It is essential to understand that BMI does not measure a person’s body fat directly. For many years now, BMI has been criticized for being an inaccurate measure of a person’s body fat content since it does not take into account many other important factors that are discussed below. Health experts worldwide criticize BMI for being an overly simple method of screening and not indicating correctly what being healthy really means. Many even claim that BMI is highly outdated and inaccurate and, therefore, should not be used for fitness and medical purposes.

BMI was developed by a Belgian mathematician named Lamber Adolphe Jacques Quetelet in 1832. Quetelet developed this measurement scale to easily estimate the degree of obesity and overweight in a certain population to allow governments to decide where to invest their health and financial resources in a more beneficial way.⁽⁴⁾ However, what most people often forget is that Quetelet had stated at the time of developing this scale that BMI was not helpful in studying single individuals, but instead, it was best for getting an idea about a population’s overall health. However, over the years, it began to be used widely for measuring individual health.

The BMI formula is as follows: BMI = weight (kg) / height (m2)

After calculating BMI, you can then compare it to the globally used BMI scale that lets you determine where you fall within the weight range. The BMI classification and range are as follows:

• BMI range less than 18.5 – classified as underweight – high risk of poor health
• BMI range between 18.5 to 24.9 – classified as normal weight – low risk of poor health
• BMI range between 25.0 to 29.9 – classified as overweight – low to moderate risk of poor health
• BMI range between 30.0 to 34.9 – classified as obese class I or moderately obese – high risk of poor health
• BMI range between 35.0 to 39.9 – classified as obese class II or severely obese – very high risk of poor health
• BMI range of 40 or higher – classified as obese class III or extremely obese – extremely high risk of poor health

Based on where you fall in this BMI range, your doctor will suggest certain health and lifestyle changes if you are not within the normal weight category. In some countries, this BMI scale has been modified and used to represent their own populations. A good example of this is that Asian men and women are diagnosed to have a higher risk of heart disease even when they are at a low BMI, as compared to non-Asian populations.^(5, 6)

While the BMI scale can provide doctors with an overview of a person’s health simply based on their weight, it does not take into consideration many other important factors, including:

• Age
• Bone density
• Muscle mass
• Fat mass
• Genetics
• Racial differences
• Gender differences
• Overall body composition

There are many concerns and criticisms of the BMI scale, especially that it does not accurately identify whether a person is healthy. However, most studies have shown that a person’s risk of developing any kind of long-term disease and even premature death does go up in those who have a BMI lower than 18.5 (underweight category) or a BMI of 30.0 or above (obese). A 2017 study that looked at 103,218 deaths discovered that people with a BMI of 30.0 or higher had nearly 1.5 to 2.7 times higher risk of premature death after a follow-up of 30 years.^(7, 8) Another study looked at 16,868 participants showed that the individuals who were in the BMI obese category had a 20 percent higher risk of death from all causes, including heart disease, as compared to those individuals who had a normal BMI category.⁽⁹⁾ The same study also found that individuals who were categorized as underweight and extremely obese, or severely obese as per BMI, died at an average of 6.7 years and 3.7 years earlier, respectively.

There have been many other studies as well that have shown that having a higher than 30.0 BMI range significantly increases your risk of developing chronic health conditions like heart disease, type 2 diabetes, kidney disease, mobility issues, breathing problems, and even non-alcoholic fatty liver disease.^{(10, 11, 12, 13)}

Since most studies show that there is a significantly higher risk of chronic diseases in people who have obesity, many health experts use BMI as a general standard for determining an individual’s risk. Nevertheless, BMI should not be the only tool used to assess the risk of developing chronic diseases.^(14, 15)

Even though research typically associates a low and high BMI with higher health risks, there are many flaws and downsides to using BMI as well. These are discussed below.

1. BMI Does Not Take Into Account Other Health Factors

   The main drawback of using BMI for determining if a person is in good health or not is that this measurement indicator only provides a yes or no answer to whether an individual is of normal weight. It does not take any account essential factors like lifestyle, age, gender, genetics, medical history, and other such factors. This is why depending solely on BMI can make a doctor miss out on other essential health indicators, including heart rate, blood sugar levels, cholesterol levels, blood pressure, and inflammation levels. It may also lead to a doctor overestimating or underestimating an individual’s true health scenario.

   Another distinguishing factor that serves as a drawback is that despite the different body compositions in both men and women, where men have less fat mass and more muscle mass than women, BMI makes use of the same calculations for both genders.⁽¹⁶⁾

   At the same time, as a person gets older, the body fat mass tends to also increase naturally, while the muscle mass decreases naturally. Many studies have found that a high BMI of 23.0 to 29.9 in older adults can actually help protect them against diseases and early death.^(17, 18)

   One must also consider that by only using BMI to say a person is obese and determine their health status can lead to ignoring other factors of health, including complex sociological factors like access to nutritious and affordable food, living environment, as well as their mental health.

2. Assumption That All Weight Is Equal

   Another drawback to only using BMI to determine a person’s health status is that it assumes all weight to be equal. Even though one kilogram of muscle has the same weight as one kilo of fat, what one has to keep in mind is that muscle is denser, and it also takes up less space. Due to this, a person who is very lean, but has a higher muscle mass, might actually be heavier on the weighing scale.

   At the same time, two people of the same weight and height could have completely different physiological makeup. One could have higher fat mass while the other has high muscle mass. But, BMI does not consider this and tends to easily misclassify a person as being obese or overweight despite having low-fat and high muscle mass. This is why it is essential to consider a person’s fat, muscle, and bone mass, as well as their weight.^{(19, 20, 21)}

3. BMI Does Not Look At The Fat Distribution In The Body

   Even though having a higher BMI range is associated with poorer health, there is another factor that makes a massive difference to this result, and that is the location of the fat in the body.

   People who have fat around their stomach area have a higher risk of developing chronic diseases as compared to people who have fat stored in their thighs, hips, and buttocks. A review of 72 studies concluded that people with fat in their stomach area have a significantly higher mortality risk, while those with fat stored in their thighs, hips, and buttocks have a much lower risk.^{(22, 23, 24, 25, 26)} The authors of the study especially highlighted that BMI does not take into account where on the body the fat is stored, which is why it often misclassifies a person as being of poor health or at a high risk of disease.

BMI remains a highly criticized and controversial health measurement tool that is designed only to estimate a person’s body weight and risk of poor health. Research has shown that a high BMI does indicate a higher risk of chronic diseases, and a low BMI is also linked to poorer health outcomes. However, the fact that BMI does not consider other important health indicators like gender, age, fat mass, muscle mass, bone mass, race, genetics, and overall medical history, means that it should not be used as the sole predictor of health or obesity. So while BMI can be a helpful starting point, it should not be taken as the final verdict about your health.

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