DEXA vs InBody vs BMI: how to actually measure body composition
If you are tracking the effects of a health protocol, your measurement tool matters as much as the protocol itself.
TL;DR
- BMI tells you how heavy you are for your height — it says nothing about what that weight is made of.
- DEXA (dual-energy X-ray absorptiometry) is the research gold standard for body composition.
- InBody and similar bioimpedance devices are less precise but practical for tracking trends at home or in a gym.
What it is
Body composition refers to the ratio of fat mass to lean mass (muscle, bone, and organs) in your body. A standard BMI calculation — body mass index (your weight in kilograms divided by your height in meters squared) — tells you nothing about that ratio. It just tells you how much you weigh relative to your height.
This matters because lean muscle mass and fat mass behave very differently in the body — particularly when it comes to metabolic health, insulin sensitivity, and longevity markers.
How it works
DEXA (pronounced DEK-suh) passes two low-dose X-ray beams at different energies through your body. Different tissues absorb each beam differently. The scanner translates those differences into precise measurements of fat mass, lean mass, and bone mineral density — regionalized by limb and torso. The radiation exposure is about one-tenth of a standard chest X-ray.
Bioimpedance analysis (BIA) — the method used by InBody, Tanita, and similar devices — sends a mild electrical current through your body. Fat tissue conducts electricity poorly; lean tissue conducts it well. The device estimates composition from resistance patterns. Think of it like estimating the water content of a sponge by measuring how easily current passes through it. The analogy holds: hydration level strongly affects results, which is why time-of-day and pre-test hydration matter.
BMI is just arithmetic. Divide your weight by your height squared. No current, no scan — and therefore no information about what your weight is made of.
Who asks about it
People starting a peptide protocol, a body recomposition program, or any health intervention that is supposed to affect muscle and fat mass often ask this question. They want a baseline. They want to know whether the intervention is working. Choosing the wrong measurement tool means tracking noise instead of signal.
What the research says
A 2018 review in the Journal of Cachexia, Sarcopenia and Muscle confirmed DEXA as the preferred reference method for measuring lean mass in aging adults, with bioimpedance as an acceptable alternative for serial (repeated) tracking when cost or access limits DEXA (Buckinx et al., 2018).
A separate analysis of BMI in the context of metabolic risk found that BMI misclassifies lean body composition in roughly 1 in 4 adults studied — placing muscular individuals into "overweight" categories while missing visceral fat (fat stored around the organs) in individuals who appear to be at a healthy weight (NIH PMC, 2013).
What to know before considering it
DEXA requires access to a clinic or imaging center and a modest out-of-pocket cost (typically $50–$150 for a body composition scan in the US). InBody devices are available at many gyms and clinics and provide useful directional data when used consistently at the same time of day, with the same level of hydration.
A single measurement of any kind is a snapshot. The power is in the trend — comparing results over 6–12 months under consistent protocol conditions.
The Halftime POV
At Halftime Health, every protocol starts with a baseline. Knowing your lean mass and fat mass — not just your weight on a scale — gives your clinician a real starting point and gives you a meaningful way to track whether a protocol is working. BMI is fine for population statistics. It is not a clinical tool for individuals pursuing meaningful change.
Related reading:
- Biomarkers commonly tracked during peptide protocols
- DEXA body composition scans and peptide protocols
- Tesamorelin and visceral fat research
FAQ
Q: Is DEXA more accurate than InBody? A: DEXA is the research reference standard. InBody-style devices are less precise but practical and good for tracking trends over time.
Q: What is wrong with BMI? A: BMI cannot distinguish fat from muscle. Two people can have identical BMI scores but completely different body compositions.
Q: How often should I get a DEXA scan on a protocol? A: Every 6–12 months is typical. More frequent scans add cost without adding much useful signal unless you are in an active study.
Disclaimer
This article is educational and is not medical advice. Compounded medications are not FDA-approved. Clinical outcomes depend on individual factors and require physician evaluation. Results vary. Halftime Health is launching soon — join the waitlist to get updates.
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Sources
Frequently asked questions
Is DEXA more accurate than InBody?
DEXA is generally considered the reference standard for body composition in research settings. InBody and similar bioimpedance devices are less accurate but more accessible and good for tracking trends over time.
What is wrong with BMI?
BMI measures total weight relative to height. It cannot distinguish fat from muscle. A highly trained athlete and a sedentary person of the same height and weight get the same BMI, even though their body compositions are very different.
How often should I get a DEXA scan?
Every 6–12 months is a common interval for people tracking body composition during a peptide or training protocol. More frequent scans are rarely necessary unless you are in an active clinical study.
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