#227 - AMA #40: Body composition, protein, time-restricted feeding, fasting, DEXA scans, and more
Peter Attia, joined by Nick Stenson, discusses interpreting DEXA scans, including key metrics like BMD, VAT, ALMI, and FFMI, and how to apply results to patient care. The episode also previews discussions on protein consumption and updated views on time-restricted feeding.
Deep Dive Analysis
8 Topic Outline
Introduction to AMA 40: DEXA Scans, Protein, and Time-Restricted Feeding
Understanding DEXA Scans: Purpose and Radiation Levels
Contextualizing Radiation Exposure: Everyday Sources vs. Medical Scans
Four Key Metrics Provided by a DEXA Scan
Importance of Bone Mineral Density (BMD) Data from DEXA
Visceral Adipose Tissue (VAT) as a Risk Indicator
Lean Mass Indices: ALMI and FFMI Explained
Optimal Frequency and Specific Data Requirements for DEXA Scans
5 Key Concepts
DEXA Scan
A Dual-energy X-ray Absorptiometry (DEXA) scan is a low-powered, moving X-ray technology used to assess body composition. It distinguishes between bone, fat, and other tissues based on their density, providing insights into body fat percentage, bone mineral density, and lean mass.
Millisieverts (mSv) and Microsieverts (µSv)
These are units of measurement for ionizing radiation exposure. A microsievert is one-thousandth of a millisievert, used to quantify radiation from various sources like medical scans, flights, and even natural environmental exposure.
Visceral Adipose Tissue (VAT)
VAT is an estimate of the fat located within the torso, surrounding internal organs. It is considered a more significant indicator of metabolic risk compared to subcutaneous fat, despite being a relatively small fraction of total body fat.
Appendicular Lean Mass Index (ALMI)
ALMI is a measure of lean tissue (muscle) specifically in the extremities (arms and legs). It is calculated by dividing the total lean tissue in the limbs by the individual's height in meters squared, reported in kilograms per meter squared (kg/m²).
Fat-Free Mass Index (FFMI)
FFMI represents the total mass of an individual that is not fat. It is calculated by dividing the total fat-free mass by the individual's height in meters squared, also reported in kilograms per meter squared (kg/m²).
5 Questions Answered
A DEXA scan is a low-powered, moving X-ray that measures the density of tissues (bone, fat, and other) by assessing how many electrons hit a plate behind the body, allowing for body composition analysis.
A DEXA scan involves extremely low radiation, typically less than 20 microsieverts, which is significantly less than a mammogram, a chest X-ray, or even a cross-country flight, making it a very safe procedure.
A DEXA scan provides four main pieces of information: body fat percentage, bone mineral density (BMD), visceral adipose tissue (VAT), and lean mass indices like appendicular lean mass index (ALMI) and fat-free mass index (FFMI).
A DEXA scan should typically be done once, or at most twice, per year; more frequent scans, such as every six weeks, are generally considered a total waste of time.
Segmented BMD data for specific areas like the hip and lumbar spine is crucial for accurately diagnosing osteopenia or osteoporosis, as a total body BMD Z-score can mask localized issues and provide inadequate clinical assessment.
6 Actionable Insights
1. Consult Healthcare Professionals
Always seek the assistance of your healthcare professionals for any medical conditions and do not disregard or delay obtaining professional medical advice, as the podcast content is for general informational purposes only and not a substitute for medical advice, diagnosis, or treatment.
2. Interpret DEXA Beyond Body Fat
When reviewing DEXA scan results, look beyond just body fat percentage and pay close attention to bone mineral density (BMD), visceral adipose tissue (VAT), and appendicular lean mass index (ALMI) or fat-free mass index (FFMI), as these provide more critical health insights.
3. Request Segmented BMD Data
If you have any concerns about bone mineral density (BMD), ensure the DEXA scan provider can give segmented information (e.g., hip and lumbar spine data), as total body Z-score alone is insufficient for clinical assessment or diagnosis of conditions like osteopenia or osteoporosis.
4. Annual DEXA Scan Frequency
Perform a DEXA scan only once or twice per year, as doing it more frequently (e.g., every six weeks) is a total waste of time due to its low risk and the rate of change in body composition.
5. Re-evaluate Time-Restricted Feeding
Consider that views on time-restricted feeding (TRF) are becoming more nuanced, moving away from a rigid stance to a more complex understanding, which may impact personal TRF practices.
6. DEXA Scan Safety
Do not be concerned about the radiation exposure from a DEXA scan, as it is extremely low (typically less than 20 microsieverts), making it a very safe and low-risk technology with effectively zero risk.
3 Key Quotes
DEXA is a virtually radiation-free technology. It is insanely low.
Peter Atiyah
Visceral fat is a relatively small fraction of total body fat. But it's important to get that right because it's so much more indicative of risk.
Peter Atiyah
This is a type of scan that you would do once, maybe twice per year. It has the capacity to distinguish effectively three things, bone, fat, and other.
Peter Atiyah