Body Mass Index: Is BMI a Good Health Assessment Tool?

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Body mass index (BMI) is used as a standard tool for health assessment in most healthcare facilities. But is it a really good tool?

BMI Explained

The medical screening tool is used to measure one's height and weight ratio to estimate one's body fat. BMI is calculated by measuring weight in kilograms (kg) and then dividing it by the square of height in meters (m2). There are also online BMI calculators available, such as the one that the National Institutes of Health provides.

When one's BMI is calculated, the results are compared to the BMI scale to determine if one falls under the "normal" range of weight. A BMI range below 18.5 signifies being underweight, while a BMI range of 18.5 to 24.9 is classified as normal weight. The classification of overweight has a BMI range of 25.0 to 29.9, while obesity has three different classes, involving BMI ranges of 30.0 to 34.9, 35.0 to 39.9, and 40 or more.

For the majority of people, BMI correlates with body fat. A higher BMI could indicate a higher level of body fat.

While BMI has been used as a go-to assessment tool for health based on one's body size, it has been criticized widely due to its oversimplification of health. In fact, there are several individuals who claim that the tool is inaccurate and outdated.

Despite these concerns, several studies have revealed that a person's risk of premature death and chronic disease does go up when their BMI is below 18.5 or above 30.0. For one, a 2017 study involving a retrospection on 103,218 deaths found that those with a BMI of 30.0 or more had a 1.5 to 2.7 times higher risk of death after a follow-up worth 30 years.

There are also other studies that show that a BMI that is higher than 30.0 may significantly boost risk of chronic health issues, such as heart disease and type 2 diabetes. On top of this, a 5% to 10% decrease in one's BMI has been linked to decreased rates of heart disease, type 2 diabetes, and metabolic syndrome.

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Is BMI a Good Tool?

While there are studies that have associated low and high BMI with health risks, BMI has several flaws.

For one, BMI only gives "yes" or "no" answers regarding whether a person has a normal weight. It does not account for a person's sex, age, genetics, lifestyle, medical history, and other factors. BMI also does not consider the varying body compositions of men and women. Hence, relying on this tool could lead to missing out on other crucial measurements of health.

The tool also assumes that all types of weight are equal. However, it is important to know that, though a kilogram of muscle may have the same weight as a kilogram of fat, muscle takes up less space due to its density. Hence, a lean person with high muscle mass may have a heavier BMI. If BMI is the only metric that is considered, a person can easily be misclassified as obese or overweight despite having low fat mass.

VMI could also not accurately reflect the health of some ethnic and racial groups. For one, several studies have shown that those with Asian roots have a higher chronic disease risk at lower cut-off points in the BMI. This is compared to white individuals. In fact, the Asia-Pacific BMI guidelines were developed by the World Health Organization in order to offer alternative cut-off points for BMI.

Other Alternatives

While BMI is full of flaws, it is still a standard health assessment tool due to its cost-effectiveness, convenience, and accessibility. However, there are some alternatives that could better indicate the health of a person.

Other alternatives include waist circumference, waist-to-hip ratio, body fat percentage, and lab tests.

That said, while BMI could be a helpful starting point, it should not be the sole tool for gauging one's health.