Rethinking BMI and Body Composition

BMI has long been the go-to metric for classifying obesity. It's widely used by insurance plans to determine eligibility for bariatric surgery and has been a staple in medical organizations for assessing health risks. Typically, a BMI of 25 or greater is used to define overweight, while a BMI of 30 or greater defines obesity.

However, BMI is far from perfect.

It doesn’t measure excess adipose tissue, account for muscle mass, or indicate tissue and organ function. Despite its historical use in estimating obesity on a population level, BMI is not be the best tool for individual health assessment.

The Origins of BMI

BMI was created in 1832 by Belgian astronomer and mathematician Adolphe Quetelet as the “Quetelet Index.” It was designed as a population-level tool, not for individual health assessment. Yet, in 1972, physiologist Ancel Keys reintroduced it as the Body Mass Index, and it quickly became a standard measure in the medical community.

Moving Beyond BMI: Why Body Composition Matters

If we shouldn’t rely on BMI alone, what should we measure? The AMA now recommends using BMI alongside other metrics like visceral fat, body adiposity, and waist circumference. But before diving into these alternatives, let's clarify what body composition is.

Body composition refers to the proportions of fat, muscle, bone, and water in your body. Understanding these components is key to assessing overall health.

Common Methods for Measuring Body Composition

1. Hydrostatic Weighing: Considered the gold standard by the American College of Sports Medicine, this method involves weighing a person on dry land and then in water. It's highly accurate but time-consuming and not widely accessible.

2. BOD POD: This technique uses air displacement in a sealed chamber to measure body fat percentage. It’s quick and accurate but requires technical expertise and can be costly. Plus, the skin-tight suit required may be uncomfortable for some patients.

3. DEXA Scan: Known for measuring bone density, DEXA scans also provide detailed body composition data. It offers insights into fat distribution across different body parts but can be expensive.

4. Bioimpedance Analysis (BIA): This method measures how fast an electrical current moves through your body, differentiating between muscle and fat. BIA devices are becoming more common in medical offices and fitness centers, making this a more accessible option.

5. Skinfold Test: A simple and low-cost method using calipers to measure skinfold thickness at various body sites. However, accuracy varies depending on the skill of the person taking the measurements.

6. Waist-to-Hip Ratio (WHR): This straightforward measurement compares the circumference of the waist to that of the hips. A WHR above 0.9 for men and 0.85 for women indicates higher health risks. While easy to use, WHR has its limitations, particularly in individuals under 5 feet tall or with a BMI over 35 and it should not be used in children.

7. Whole Body MRI: The gold standard for measuring skeletal muscle and visceral fat, but it’s expensive and not feasible for most patients.

What Should We Measure Instead?

Given the limitations of BMI and body composition metrics, it’s crucial to screen for secondary causes of obesity through a thorough history and physical exam. These could include:

• Hormonal abnormalities
• Psychiatric disorders
• Genetic syndromes
• Medication side effects

Additionally, assess weight-related comorbidities such as:

• NAFLD
• Sleep apnea
• Prediabetes/DM
• Hypertension
• Reflux

The Power of Non-Scale Victories

While body composition and weight metrics are important, they shouldn’t be the sole focus. Non-scale victories can often provide a more meaningful measure of success, particularly for patients striving to improve their health. These victories include:

• Increased energy levels
• Boosted confidence
• Improved sleep quality
• Better fit of clothing
• Greater ability to engage in activities with loved ones
• Feeling sexy
• Enhanced endurance

Conclusion

Next time you’re working with a patient focused on weight loss, think beyond the scale. Encourage them to track goals that truly matter to them, like how they feel, move, and live their daily lives. By shifting the focus from numbers to overall well-being, you can help your patients achieve more sustainable and meaningful results.

If you'd like to go deeper on this topic, take a listen to this episode.