Why Body Mass Index (BMI) is Flawed: BMI Explained

Body Mass Index or BMI, is often presented as a straightforward, black-and-white measure of health. Healthcare providers, fitness trainers, and even insurance companies frequently use BMI to make judgments about one’s health. However, this popular health metric has its own set of limitations.

How is BMI Calculated

The BMI is commonly calculated using the metric system. However, you can also calculate BMI using inches for height and pounds for weight.

• Measure Your Weight: Find out your weight in pounds.
• Measure Your Height: Measure your height in inches. Make sure you stand up straight while measuring your height. If you know it in centimeters (cm), convert cm to inches.
• Square Your Height: Multiply your height in inches by itself (i.e., square it).
• Divide Weight by Squared Height: Divide your weight in pounds by your squared height in inches.
• Multiply by 703: Multiply the result from step 4 by 703.

The resulting number is your BMI, which you can then use to categorize your weight status according to common BMI categories:

• Underweight: BMI < 18.5
• Normal weight: BMI 18.5–24.9
• Overweight: BMI 25–29.9
• Obesity I: BMI 30–34.9
• Obesity II: BMI 35–39.9
• Extreme Obesity: BMI ≥ 40

Flaws of BMI

Here’s a look at why BMI is considered flawed.

1. Does Not Account for Body Composition

BMI fails to distinguish between muscle and fat. Two individuals with the same BMI might have vastly different body compositions. Athletes and bodybuilders often have high BMIs due to muscle mass but are in excellent health. Conversely, someone with a ‘normal’ BMI might still have high body fat and the accompanying health risks.

2. Ignores Fat Distribution

Another crucial shortcoming of BMI is that it does not consider where body fat is distributed. Numerous studies suggest that visceral or abdominal fat poses more health risks than subcutaneous fat stored in other areas.

3. Inapplicable to All Age Groups and Ethnicities

BMI is often misleading for older adults, whose muscle mass usually declines with age, and for certain ethnic groups who may have different body compositions. For example, many Asian populations tend to have higher body fat percentages at the same BMIs compared to individuals of European descent.

4. Poor Indicator of Health Outcomes

BMI is often criticized for being too reductionist. It reduces the complex nature of health and well-being to a single number. It fails to account for other medical metrics like blood pressure and cholesterol levels.

Because BMI is often used as a preliminary screening tool, its limitations can lead to incorrect medical advice. For instance, an individual with a high BMI may be wrongly categorized as being at high risk for heart disease. On the other hand, someone with a low or normal BMI might be overlooked for additional testing, even if they have other risk factors.

BMI alone is not a reliable predictor of mortality or the risk of ailments like cardiovascular disease.

5. Promotes Weight Stigma

Using BMI as a health measure can contribute to weight stigma and discrimination. It may lead to unfair judgments and contribute to body dissatisfaction.

Key Takeaways

While BMI can offer a quick and easy assessment of weight status, its limitations make it an unreliable indicator of individual health. Healthcare professionals and individuals should consider multiple metrics. There should be a more holistic approach to healthcare.

• BMI can mistakenly categorize muscular individuals as overweight or obese.
• The measure doesn’t consider where fat is located.
• BMI is not universally applicable, as it does not adjust for varying factors like age and ethnicity that can influence health.
• It is not an accurate predictor of health outcomes.
• The use of BMI can lead to discrimination.