Ask the Expert: Understanding Body Composition with Grant Tinsley, PhD

Body composition is a nuanced topic that goes far beyond the numbers we often see in clinical settings. In this “Ask the Expert” series, Dr. Grant Tinsley, Director of the Energy Balance and Body Composition Laboratory at Texas Tech University, shares his expertise on the complexities of assessing and interpreting body composition, addressing misconceptions, and offering practical guidance for healthcare providers and patients alike. To hear the full podcast conversation on ‘In the Know with Nina’, see https://secambca.com/body-composition-assessment-dexa-bioimpedance/

Breaking Down Body Composition Terminology 

Body composition refers to what our body mass is made of—beyond the simplistic number on the scale. Dr. Tinsley explains that body composition can be described at different levels, with two commonly discussed categories being:

Molecular Level: This breaks the body into molecular components, such as fat, water, protein, and bone mineral. Fat-free mass (FFM) encompasses everything except fat, including water (the largest component), protein, and bone. Importantly, FFM does not exclusively represent skeletal muscle, a common misunderstanding.

Organ-Tissue Level: This level examines body composition based on anatomical parts, like skeletal muscle or adipose tissue. Measuring these components often requires imaging techniques such as MRI or CT scans.

Confusion frequently arises when terms like “fat-free mass,” “lean body mass,” and “skeletal muscle mass” are used interchangeably. This conflation can lead to misinterpretations of study results, particularly in research on obesity or weight loss interventions. Dr. Tinsley emphasizes that precision in terminology is vital to avoid overgeneralized conclusions, such as assuming all FFM loss equates to muscle loss.

Gold Standard or Guiding Principle? 

When it comes to assessing body composition, healthcare providers often refer to “gold standard” methods. Dr. Tinsley points out that while terms like “criterion method” or “reference method” are more accurate, even these techniques have limitations.

For example:

Magnetic Resonance Imaging (MRI): Considered a reference method for organ-tissue level assessment, MRI is powerful but not infallible. It provides high-resolution data on skeletal muscle and adipose tissue but remains impractical for most clinics due to cost and accessibility.

DEXA (Dual-Energy X-ray Absorptiometry): Widely recognized in clinical settings, DEXA offers useful anatomical insights and can differentiate between fat, lean tissue, and bone mineral content. However, its 2D imaging introduces estimation errors, particularly for body parts containing bone. Additionally, the physical dimensions of DEXA scanners may limit their use for individuals with larger body sizes.

For practical applications, providers often turn to accessible tools like bioimpedance analysis (BIA), which, when properly validated, can provide robust data for clinical use.

Bioimpedance Analysis: Nuances and Applications 

Bioimpedance analysis (BIA) has gained traction as an efficient, non-invasive method for assessing body composition. Dr. Tinsley stresses that not all BIA devices are created equal. Professional-grade devices, like those from SECA, are equipped with advanced algorithms validated through rigorous scientific methods, including multi-compartment models, MRI, and total body water dilution studies.

In contrast, consumer-grade devices, often sold for home use, lack this level of precision. “Broad conclusions about bioimpedance as a category are unfair,” Dr. Tinsley notes, highlighting the importance of distinguishing between professional and consumer devices.

Professional-grade BIA devices offer unique advantages, such as:

Segmental Analysis: Providing data on specific body regions (e.g., limbs vs. trunk).

Multi-Frequency Technology: Differentiating fluid compartments and enhancing accuracy.

Health Markers: Metrics like phase angle, which correlate with cellular health and overall well-being.

Tracking Change Over Time 

One of the most valuable uses of body composition assessment is tracking changes during interventions such as weight loss or muscle-building programs. However, accuracy depends heavily on standardization.

Key considerations include:

Consistent Conditions: Patients should be assessed under similar conditions (e.g., fasted, rested, and with controlled fluid intake).

Minimizing Biological Noise: Small changes in hydration or recent physical activity can skew results, especially when tracking subtle body composition shifts.

Dr. Tinsley notes that while professional BIA devices can reliably track changes over time, healthcare providers must adhere to strict protocols to ensure accurate and meaningful data.

Beyond the Numbers 

As the field of body composition evolves, there is growing recognition of the need to look beyond simple metrics like body fat percentage, and explore the importance of measures such as visceral adipose tissue (VAT) and muscle mass, which provide deeper insights into a patient’s health.  Tools like professional BIA analyzers can also capture unique physiological markers, helping providers better understand a patient’s cellular health and functional status. These insights are invaluable for tailoring interventions and improving patient outcomes.

A Collaborative Future 

As clinicians and researchers continue to refine body composition assessment methods, accessibility and education remain critical. We envision a future where these tools are seamlessly integrated into clinical practice, empowering providers to deliver personalized, data-driven care.  Together, let’s move beyond BMI and weight to unlock the full potential of body composition assessment in improving health outcomes.

For more information on Dr. Tinsley’s work, visit his website at granttinsley.com or follow him on LinkedIn and Instagram (@grant_tinsley_phd).