The Limitations of BMI

Is BMI the best way to measure health? Many of us use it, but does it tell the whole story? If you’ve ever started a weight-loss regimen, you’ve probably heard the term BMI. An acronym for Body Mass Index, BMI is a calculation used by both consumers and health professionals to gauge whether you’re at a healthy weight. While BMI provides a quick snapshot of your weight status, it has limitations and shouldn’t be the only metric to determine your overall health.

How Is BMI Calculated?

Two numbers go into a BMI calculation: your height (in inches) and weight (in pounds). The formula is:

Weight (lb) / height (in)² x 703

For a person weighing 240 pounds and standing six feet, one inch (73 inches) tall, the calculation would be about 32.

To Interpret BMI, Refer to These Ranges:

• Underweight = 18.5 or below
• Healthy weight = 18.5 to 24.9
• Overweight = 25 to 29.9
• Obese = 30 or greater

Since 32 falls into the obese range, a person with this BMI might consider weight management interventions. However, BMI doesn’t account for several key factors that impact overall health.

What BMI Doesn’t Measure

Since BMI is based solely on height and weight, it oversimplifies health assessment. Here’s what it fails to consider:

• Body Fat Distribution: A 2020 study published in the British Medical Journal found that higher amounts of abdominal fat increase the risk of premature death, even in people with a “normal” BMI. If you have an apple-shaped body (weight concentrated in the midsection), your risk of cardiovascular disease, high blood pressure, and metabolic disorders may be higher—even if your BMI is within the “healthy” range.
• Muscle Mass: Muscles are denser than fat, which means athletes and muscular individuals may have high BMIs despite low body fat percentages. This could place a bodybuilder and a sedentary person of the same weight in the same BMI category, even though their body compositions are drastically different.
• Age: We lose muscle mass and may store fat differently as we age. Older adults may have lower BMIs but still carry excess body fat, making BMI a less reliable health metric for seniors.
• Gender: BMI does not account for the body mass and fat composition differences between male and female patients and, therefore, can render an inaccurate result.

Alternatives to BMI

Now that you know BMI’s limitations, what other ways can you assess health? Here are more accurate methods:

• DXA (Dual-Energy X-ray Absorptiometry) Analysis: This advanced body scan measures body fat percentage, lean muscle mass, and bone density. It’s a gold standard for assessing body composition, but due to the radiation exposure, it should only be performed every two years.
• Caliper Skinfold Test – This method uses calipers to measure the thickness of fat deposits at specific body sites. While less precise than DXA, it provides a general estimate of body fat percentage.
• Hydrostatic Weighing (Underwater Weighing): This test compares body weight on land to underwater. Since fat is less dense than water, people with higher body fat percentages will weigh less in water. This is one of the most accurate methods for determining body fat composition but requires specialized equipment.
• Waist Size – This can be very useful in determining cardiovascular risk.
• Waist-to-Height Ratio

The Bottom Line

While BMI is a quick and easy metric, it provides an incomplete picture of health. Dr. Craig Chang and the Advanced Bariatric & Surgical Specialists team offer a comprehensive analysis to help you understand your health status and set realistic goals.

Call or email us to schedule a consultation.