The Longevity Index

DEXA Scans

The TL;DR

DEXA (Dual-Energy X-ray Absorptiometry) scans provide the gold-standard measurement of body composition, including fat mass, lean mass, bone mineral density, and visceral adipose tissue. These metrics are powerful predictors of longevity, enabling early detection of sarcopenia, osteoporosis, and dangerous visceral fat accumulation. Annual DEXA scans allow precise tracking of changes that simple scales cannot detect, making them an essential tool for anyone serious about optimizing healthspan.

Accessibility Level

Level 2 (Optimization): DEXA scans require specialized equipment and represent an investment in precision health tracking. Master your foundational exercise and nutrition protocols first, then use DEXA to quantify progress and identify areas for targeted intervention.

What Is a DEXA Scan?

The Technology Explained

Dual-Energy X-ray Absorptiometry, commonly known as DEXA or DXA, is an imaging technology that uses two different X-ray energy levels to distinguish between different tissue types in the body. Originally developed in the 1980s for measuring bone mineral density (BMD), DEXA has evolved into the clinical and research gold standard for comprehensive body composition analysis (Shepherd et al., 2017).

During a DEXA scan, the patient lies on a padded table while a mechanical arm passes over the body, emitting low-dose X-ray beams at two distinct energy levels. Different tissues (bone, fat, lean mass) attenuate these beams differently, allowing the software to calculate precise quantities of each tissue type. The entire scan typically takes 10-20 minutes and exposes the patient to approximately 1-10 microsieverts of radiation, roughly equivalent to 1-3 hours of natural background radiation or a cross-country flight (Toombs et al., 2012).

Why DEXA Is the Gold Standard

DEXA has earned its reputation as the reference method for body composition assessment for several reasons:

  • Precision: DEXA provides coefficients of variation (CV) of 1-2% for fat mass and lean mass measurements, making it highly reproducible (Nana et al., 2015).
  • Regional Analysis: Unlike other methods, DEXA provides segmental data, breaking down composition by arms, legs, trunk, and android/gynoid regions.
  • Bone Assessment: DEXA uniquely measures bone mineral content and density, critical for assessing osteoporosis risk.
  • Visceral Fat Quantification: Modern DEXA systems estimate visceral adipose tissue (VAT), a key longevity marker.
  • Low Radiation: The radiation exposure is minimal compared to CT scans while providing comparable accuracy for body composition.

Key Insight

While bioelectrical impedance scales and calipers can track trends, they cannot match DEXA’s accuracy or provide the granular regional data essential for identifying specific areas of concern like visceral fat accumulation or asymmetric muscle loss.

What DEXA Measures

Body Composition: The Three Compartments

DEXA divides body mass into three primary compartments:

1. Fat Mass (FM) Total adipose tissue throughout the body, including subcutaneous fat (beneath the skin) and visceral fat (surrounding organs). DEXA reports this as both absolute mass (kg/lbs) and as a percentage of total body weight.

2. Lean Mass (LM) Also called fat-free soft tissue, this includes skeletal muscle, organs, skin, and water. While often used interchangeably with “muscle mass,” lean mass is slightly broader. Appendicular lean mass (ALM), the lean tissue in arms and legs, serves as a proxy for skeletal muscle and is crucial for sarcopenia diagnosis.

3. Bone Mineral Content (BMC) The total mineral content of the skeleton, reported in grams. This differs from bone mineral density, which accounts for bone area.

Bone Mineral Density (BMD)

BMD represents the concentration of minerals (primarily calcium and phosphorus) in bone tissue, expressed as grams per square centimeter (g/cm2). DEXA measures BMD at specific sites, typically:

  • Lumbar Spine (L1-L4): Highly metabolically active trabecular bone, sensitive to changes.
  • Femoral Neck: The narrow section connecting the femur head to the shaft, a common fracture site.
  • Total Hip: Includes femoral neck, trochanter, and intertrochanteric regions.
  • Forearm (Radius): Sometimes used when hip or spine measurements are compromised.

Results are reported as:

  • T-score: Standard deviations from the mean BMD of a healthy 30-year-old adult of the same sex. A T-score of -1.0 or above is normal; -1.0 to -2.5 indicates osteopenia; below -2.5 indicates osteoporosis (Kanis et al., 2019).
  • Z-score: Standard deviations from the mean of age-matched and sex-matched individuals, useful for identifying whether bone loss is greater than expected for age.

Visceral Adipose Tissue (VAT)

Perhaps the most longevity-relevant metric provided by modern DEXA systems, VAT estimation quantifies the fat stored within the abdominal cavity surrounding vital organs. Unlike subcutaneous fat, visceral fat is metabolically active, secreting inflammatory cytokines and contributing to insulin resistance, cardiovascular disease, and systemic inflammation (Tchernof & Despres, 2013).

DEXA estimates VAT in the android region (roughly from the pelvis to above the lowest rib) and reports it as:

  • VAT Mass: Absolute weight in grams or kilograms.
  • VAT Volume: Cubic centimeters of visceral fat.
  • VAT Area: Cross-sectional area, often used in research.

The Hidden Danger

Individuals with normal BMI can harbor dangerous levels of visceral fat, a condition sometimes called “TOFI” (Thin Outside, Fat Inside). DEXA reveals this hidden risk that scale weight and even body fat percentage alone cannot detect.

Why These Metrics Matter for Longevity

Sarcopenia: The Silent Thief of Healthspan

Sarcopenia, the age-related loss of muscle mass and function, is one of the most significant threats to healthy aging. Beginning around age 30, adults lose approximately 3-8% of muscle mass per decade, with acceleration after age 60 (Volpi et al., 2004). This decline predicts:

  • Increased Mortality: Low appendicular lean mass is independently associated with higher all-cause mortality. A meta-analysis of 31 studies found that sarcopenia increased mortality risk by 60% in older adults (Beaudart et al., 2017).
  • Functional Decline: Muscle loss leads to falls, fractures, loss of independence, and reduced quality of life.
  • Metabolic Dysfunction: Skeletal muscle is the primary site of glucose disposal; less muscle means greater insulin resistance and metabolic disease risk.
  • Reduced Resilience: Lower muscle reserves compromise the body’s ability to recover from illness, surgery, or injury.

The European Working Group on Sarcopenia in Older People (EWGSOP2) recommends DEXA as a preferred method for confirming low muscle quantity, using appendicular lean mass indexed to height squared (ALM/height2) as a key diagnostic criterion (Cruz-Jentoft et al., 2019).

Osteoporosis: Building a Fracture-Resistant Skeleton

Osteoporosis affects approximately 200 million people worldwide and is responsible for 8.9 million fractures annually (Kanis et al., 2019). Hip fractures in particular carry devastating consequences for longevity:

  • One-Year Mortality: 20-30% of elderly patients die within one year of a hip fracture (Haentjens et al., 2010).
  • Loss of Independence: Only 40% of hip fracture survivors regain their pre-fracture level of function.
  • Cascade Effect: One fracture significantly increases risk of subsequent fractures.

DEXA enables early detection of declining bone density, allowing intervention through resistance training, nutritional optimization, and when necessary, pharmaceutical treatment before fractures occur. Studies demonstrate that bisphosphonate therapy, initiated based on DEXA findings, reduces vertebral fracture risk by 40-70% and hip fracture risk by 40-50% (Black & Rosen, 2016).

Visceral Adiposity: The Metabolic Danger Zone

Visceral adipose tissue is not merely stored energy. It functions as an endocrine organ, secreting pro-inflammatory adipokines including interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and resistin (Tchernof & Despres, 2013). Elevated VAT is associated with:

  • Cardiovascular Disease: VAT independently predicts coronary artery disease, even after adjusting for BMI and total body fat (Neeland et al., 2019).
  • Type 2 Diabetes: Visceral fat strongly correlates with insulin resistance and predicts diabetes development.
  • Cancer Risk: Higher VAT is associated with increased risk of colorectal, breast, and other cancers.
  • Systemic Inflammation: VAT-derived cytokines contribute to the chronic low-grade inflammation (“inflammaging”) that accelerates biological aging.
  • Cognitive Decline: Visceral adiposity is linked to reduced brain volume and increased dementia risk.

Critically, VAT can be preferentially reduced through lifestyle interventions, particularly exercise and dietary modification, even when total body weight remains stable (Vissers et al., 2013). DEXA quantifies this targeted fat loss that scales cannot detect.

How to Interpret DEXA Results

Understanding Your Report

A typical DEXA report includes several sections:

Body Composition Summary

MetricWhat It Means
Total MassYour total body weight
Fat MassTotal fat tissue (kg/lbs and percentage)
Lean MassFat-free soft tissue (muscle, organs, water)
BMCBone mineral content
Body Fat %Fat mass divided by total mass

Regional Analysis Breaks down fat and lean mass by body segment (arms, legs, trunk, android, gynoid), enabling identification of asymmetries or regional imbalances.

Android/Gynoid Ratio (A/G) The ratio of fat in the abdominal region (android) to the hip/thigh region (gynoid). Higher ratios indicate more central adiposity and increased metabolic risk. Generally, an A/G ratio below 1.0 is considered favorable.

VAT Estimates Reported in mass (grams), volume (cm3), or area (cm2). Lower values are better; specific thresholds vary by age, sex, and the DEXA system used.

Reference Ranges and Optimal Targets

MetricGeneral Population “Normal”Longevity-Optimized Target
Body Fat % (Men)18-24%10-20% (depending on age)
Body Fat % (Women)25-31%18-28% (depending on age)
ALM Index (Men)>7.0 kg/m2>7.5 kg/m2
ALM Index (Women)>5.5 kg/m2>6.0 kg/m2
T-score (BMD)> -1.0> -0.5 (building bone reserve)
VAT MassVaries by systemLower 25th percentile for age
A/G Ratio<1.0<0.8 (lower is better)

Context Matters

Optimal ranges depend on individual factors including age, sex, athletic goals, and health status. A competitive athlete may target different body fat percentages than someone focused purely on longevity. Work with a qualified healthcare provider to interpret your results in context.

Tracking Changes Over Time

The true power of DEXA lies in longitudinal tracking. A single scan provides a snapshot; serial scans reveal trajectories. When comparing scans:

  • Use the Same Facility: Different DEXA machines may produce slightly different absolute values.
  • Consistent Conditions: Same time of day, hydration status, and positioning protocols.
  • Focus on Trends: Small changes between scans may fall within measurement error; look for consistent patterns over 2-3 scans.
  • Precision Error: Ask your facility about their coefficient of variation; changes smaller than 2x the CV may not be meaningful.

How Often to Get Scanned

PopulationFrequencyRationale
General Health OptimizationAnnuallyTrack year-over-year changes in composition
Active InterventionEvery 6 monthsMonitor response to new exercise or diet protocols
Postmenopausal WomenAnnuallyHigher osteoporosis risk; track BMD closely
Men Over 65AnnuallySarcopenia and osteoporosis risk increases
Athletes/Bodybuilders2-4x per yearOptimize training and nutrition periodization
Post-Injury/SurgeryBefore and after rehabQuantify muscle recovery

Annual scanning is the most commonly recommended frequency for individuals focused on longevity. This cadence balances meaningful data collection with practical considerations of cost and time. More frequent scanning (every 6 months) may be warranted during active interventions such as initiating a resistance training program or significant dietary change.

Avoid Over-Testing

Scanning more frequently than every 3-4 months is generally unnecessary for most people. Changes in bone density especially require 12-24 months to manifest reliably.

Where to Get DEXA Scans

Commercial Providers

BodySpec

  • Mobile DEXA trucks serving multiple metropolitan areas
  • Focus on body composition (some locations also offer BMD)
  • Typically $45-50 per scan
  • Convenient locations (gyms, parking lots, corporate offices)
  • Online portal for tracking results over time

DexaFit

  • Fixed locations in major US cities
  • Comprehensive testing including DEXA, VO2 max, and metabolic rate
  • Higher price point ($75-150 per scan)
  • Additional services like 3D body scanning
  • Detailed reports with trend analysis

Medical and Research Facilities

University Research Centers Many universities with exercise science, nutrition, or gerontology programs offer DEXA scans to the public, often at reduced rates. These facilities typically use research-grade equipment and protocols.

Hospitals and Radiology Centers For bone density specifically, medical facilities offer DEXA as part of osteoporosis screening. Insurance may cover BMD scans for qualifying individuals (postmenopausal women, men over 70, those with risk factors). Body composition analysis is typically not covered.

Specialty Health Clinics Longevity-focused clinics, sports medicine practices, and functional medicine centers increasingly offer DEXA as part of comprehensive health assessments.

Gyms and Fitness Centers

Some high-end fitness facilities and boutique gyms now offer on-site DEXA scanning or partner with mobile services. This can be convenient but verify that qualified technicians operate the equipment and provide proper interpretation.

Cost Considerations

Provider TypeTypical Cost RangeNotes
BodySpec$40-50Most affordable; body composition focus
DexaFit$75-150Premium service; additional testing options
University Labs$50-100Often requires appointment; may have eligibility requirements
Medical Facilities$100-300May be covered by insurance for BMD if medically indicated
Boutique Clinics$100-250Often bundled with other services

Insurance Coverage

  • BMD scans are typically covered for women 65+, men 70+, or younger individuals with risk factors (prior fracture, steroid use, rheumatoid arthritis).
  • Body composition analysis is generally considered elective and is not covered.
  • Some HSA/FSA accounts may cover DEXA scans; check your specific plan.

Package Discounts Many providers offer multi-scan packages at reduced per-scan rates. If committing to annual tracking, purchasing a 3-5 scan package can reduce costs by 10-20%.

Preparing for a DEXA Scan

Before Your Appointment

24-48 Hours Before

  • Avoid strenuous exercise (can temporarily shift fluid distribution)
  • Maintain normal hydration (neither dehydrated nor overhydrated)
  • Avoid alcohol (affects hydration status)

Day of Scan

  • Wear lightweight, metal-free clothing (athletic wear without zippers, snaps, or underwires)
  • Remove jewelry, belts, and any metal objects
  • Fast for 2-4 hours if possible (not strictly required, but improves consistency)
  • Use the restroom before the scan (a full bladder adds water weight to results)
  • Note your weight on a calibrated scale if available

For Bone Density Scans

  • Inform the technician of any prior fractures, joint replacements, or spinal hardware
  • Do not take calcium supplements for 24 hours before (can affect measurements)

During the Scan

  • Lie still on the table as the arm passes over your body
  • Breathe normally; no breath-holding required
  • The technician will position you carefully (consistent positioning is critical for accuracy)
  • The scan takes 10-20 minutes depending on the protocol

After the Scan

  • Results are typically available immediately or within 24 hours
  • Request a copy of the full report, not just summary numbers
  • Save your results for longitudinal comparison
  • If concerning findings are identified (very low BMD, unexplained asymmetries), follow up with a healthcare provider

Limitations and Considerations

Technical Limitations

  • Hydration Sensitivity: DEXA cannot distinguish between water and lean tissue. Significant hydration changes affect lean mass readings.
  • Not True 3D: DEXA provides a 2D projection; individuals with the same fat mass but different fat distribution may show different percentages.
  • Machine Variability: Different manufacturers and software versions can produce different absolute values; always compare scans from the same machine.
  • Cannot Measure Intramuscular Fat: Fat marbled within muscle is counted as lean tissue.

Population Considerations

  • Very Obese Individuals: Table width and beam penetration may limit accuracy in individuals over 350-400 lbs.
  • Athletes with Very Low Body Fat: Precision decreases at extreme low fat levels.
  • Children and Adolescents: Reference databases are primarily developed for adults; interpretation differs in younger populations.

Radiation Exposure

While DEXA radiation is minimal (1-10 microsieverts per scan), it is not zero. Annual scanning is reasonable; more frequent scanning should be weighed against marginal additional information. DEXA is contraindicated during pregnancy.

Practical Applications

Using DEXA to Guide Interventions

If Lean Mass Is Low:

  • Prioritize resistance training with progressive overload
  • Ensure adequate protein intake (1.6-2.2 g/kg/day)
  • Consider creatine supplementation (well-evidenced for muscle building)
  • Rescan in 6-12 months to verify muscle gains

If Bone Density Is Low:

  • Initiate or intensify resistance training and impact exercise
  • Ensure adequate calcium (1000-1200 mg/day) and Vitamin D (see sunlight protocols)
  • Consult with a physician about pharmaceutical options if T-score is in osteoporotic range
  • Rescan in 12-24 months (bone changes slowly)

If Visceral Fat Is High:

  • Prioritize both resistance training and cardiovascular exercise
  • Address dietary factors, particularly refined carbohydrates and alcohol
  • Consider time-restricted eating protocols
  • Improve sleep quality (poor sleep promotes visceral fat accumulation)
  • Rescan in 6 months to track visceral fat reduction

Connected Concepts

  • Exercise: Resistance training is the primary intervention for improving both lean mass and bone density.
  • Diet: Protein intake drives muscle protein synthesis; calcium and Vitamin D support bone health.
  • Sleep: Sleep deprivation promotes muscle catabolism and visceral fat accumulation.
  • Blood Panels: Biomarkers like testosterone, IGF-1, and Vitamin D levels complement DEXA data.
  • Functional Benchmarks: Grip strength, walking speed, and other tests assess muscle function alongside mass.
  • Scales: Weight tracking provides high-frequency data between DEXA scans.
  • Protein: The building block for muscle tissue maintenance and growth.
  • Inflammation: Visceral fat drives chronic inflammation; DEXA quantifies this risk.

Implementation Checklist

Getting Started:

  • Identify DEXA providers in your area (BodySpec, DexaFit, local universities)
  • Schedule a baseline scan
  • Fast 2-4 hours before and wear appropriate clothing
  • Request the full report with regional analysis and VAT data
  • Record results in a tracking system for longitudinal comparison

Annual Protocol:

  • Schedule DEXA at the same time of year for consistency
  • Use the same facility and, ideally, the same machine
  • Maintain similar hydration and fasting status as previous scans
  • Compare year-over-year trends in lean mass, fat mass, BMD, and VAT
  • Adjust interventions based on trajectory

If Results Show Concerns:

  • Low BMD: Consult physician, intensify bone-building exercise, verify Vitamin D status
  • Low lean mass: Increase resistance training and protein intake
  • High visceral fat: Prioritize exercise, dietary modification, and sleep optimization
  • Significant asymmetries: Investigate potential injury or imbalance; consider physical therapy evaluation

References

Beaudart, C., Zaaria, M., Pasleau, F., Reginster, J. Y., & Bruyere, O. (2017). Health outcomes of sarcopenia: A systematic review and meta-analysis. PLoS One, 12(1), e0169548. https://doi.org/10.1371/journal.pone.0169548

Black, D. M., & Rosen, C. J. (2016). Clinical practice. Postmenopausal osteoporosis. New England Journal of Medicine, 374(3), 254-262. https://doi.org/10.1056/NEJMcp1513724

Cruz-Jentoft, A. J., Bahat, G., Bauer, J., Boirie, Y., Bruyere, O., Cederholm, T., … & Zamboni, M. (2019). Sarcopenia: revised European consensus on definition and diagnosis. Age and Ageing, 48(1), 16-31. https://doi.org/10.1093/ageing/afy169

Haentjens, P., Magaziner, J., Colon-Emeric, C. S., Vanderschueren, D., Milisen, K., Gruber-Baldini, A. L., … & Boonen, S. (2010). Meta-analysis: Excess mortality after hip fracture among older women and men. Annals of Internal Medicine, 152(6), 380-390. https://doi.org/10.7326/0003-4819-152-6-201003160-00008

Kanis, J. A., Cooper, C., Rizzoli, R., & Reginster, J. Y. (2019). European guidance for the diagnosis and management of osteoporosis in postmenopausal women. Osteoporosis International, 30(1), 3-44. https://doi.org/10.1007/s00198-018-4704-5

Nana, A., Slater, G. J., Stewart, A. D., & Burke, L. M. (2015). Methodology review: Using dual-energy X-ray absorptiometry (DXA) for the assessment of body composition in athletes and active people. International Journal of Sport Nutrition and Exercise Metabolism, 25(2), 198-215. https://doi.org/10.1123/ijsnem.2013-0228

Neeland, I. J., Ross, R., Despres, J. P., Matsuzawa, Y., Yamashita, S., Shai, I., … & International Atherosclerosis Society. (2019). Visceral and ectopic fat, atherosclerosis, and cardiometabolic disease: A position statement. The Lancet Diabetes & Endocrinology, 7(9), 715-725. https://doi.org/10.1016/S2213-8587(19)30084-1

Shepherd, J. A., Ng, B. K., Sommer, M. J., & Heymsfield, S. B. (2017). Body composition by DXA. Bone, 104, 101-105. https://doi.org/10.1016/j.bone.2017.06.010

Tchernof, A., & Despres, J. P. (2013). Pathophysiology of human visceral obesity: An update. Physiological Reviews, 93(1), 359-404. https://doi.org/10.1152/physrev.00033.2011

Toombs, R. J., Ducher, G., Shepherd, J. A., & De Souza, M. J. (2012). The impact of recent technological advances on the trueness and precision of DXA to assess body composition. Obesity, 20(1), 30-39. https://doi.org/10.1038/oby.2011.211

Vissers, D., Hens, W., Brinks, J., Taeymans, J., & Koppo, K. (2013). The effect of exercise on visceral adipose tissue in overweight adults: A systematic review and meta-analysis. PLoS One, 8(2), e56415. https://doi.org/10.1371/journal.pone.0056415

Volpi, E., Nazemi, R., & Fujita, S. (2004). Muscle tissue changes with aging. Current Opinion in Clinical Nutrition and Metabolic Care, 7(4), 405-410. https://doi.org/10.1097/01.mco.0000134362.76653.b2

Last updated: 2026-01-03

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