The 4% gap between an InBody 770 and a DEXA scan is real. It's also largely irrelevant for most coaching decisions. The two tools solve different problems, and most trainers are using the wrong one for what they're actually trying to do.
TL;DR: DEXA is the most accurate single-snapshot body composition measurement available outside a research lab. InBody 770 is the most practical for tracking change over time. The 3-4% gap in body fat readings between them doesn't matter as much as what you do with the numbers. If your coach doesn't know which you need and when, that's the real problem.
What DEXA Actually Measures
DEXA (Dual-Energy X-ray Absorptiometry) passes two low-dose X-ray beams at different energy levels through your body. Different tissues — bone, lean mass, fat — absorb radiation differently. The scanner builds a three-compartment model: bone mineral density, lean soft tissue, and fat mass.
Standard deviation on a well-calibrated DEXA unit is roughly ±1-2% for body fat percentage and ±1-3% for lean mass. It's also the tool used in most clinical research on body composition, which is why it's called the gold standard. When researchers need a reference measurement, they use DEXA.
The catch: DEXA has its own assumptions baked in. It assumes a fixed hydration level in lean tissue (approximately 73%). If you're dehydrated or overhydrated when you scan, the reading shifts. And the scan itself gives you a total number and a regional breakdown by limb, but it can't give you segmental lean mass — how much of your right quadricep is muscle versus connective tissue.
It's also expensive. A clinical DEXA body composition scan runs $100-200 in Toronto. And for regular monitoring — every 4-6 weeks during a training block — that adds up fast.
What InBody 770 Actually Measures
InBody 770 uses bioelectrical impedance analysis (BIA). Eight electrodes — four in the footplates, four in the hand grips — send low-level electrical signals through your body. Different tissues resist the current differently. Muscle holds water and conducts well; fat resists.
The 770 builds a segmental model: trunk, each arm, each leg — lean mass and fat mass separately, down to 0.1 kg precision. It also gives you visceral fat level (not just total fat), skeletal muscle mass, intracellular and extracellular water balance, and basal metabolic rate estimate.
The body fat reading typically runs 2-4% lower than DEXA on the same individual. That's not a flaw — it's a systematic offset that's consistent and well-documented. The important thing is that it's reproducible. Run the same person on the same InBody unit, same time of day, same hydration state, and you get highly consistent results. Test-retest reliability on InBody 770 is strong.
Where DEXA Wins: Absolute Baselines
If you want to know, with high confidence, what your body fat percentage actually is right now, DEXA is more accurate. The offset between InBody and DEXA isn't random — InBody reliably reads lower. But the magnitude varies person-to-person based on body type, hydration levels, and age. A lean, well-hydrated 28-year-old and an overweight, underhydrated 55-year-old will show different gap sizes between their InBody and DEXA readings.
For population-level research comparisons, you need DEXA. If a study says "normal body fat for males 35-45 is 18-24%," that's a DEXA-measured number. Comparing your InBody reading directly to it introduces systematic error.
For initial clinical assessment — before a major intervention, or when a client is asking "what is my actual baseline?" — a DEXA provides a more defensible answer.
Where InBody Wins: Tracking Change
This is where the argument flips. For monitoring change over time within a coaching program, InBody 770 is the better tool.
The reasons are practical. You can scan bi-weekly at the studio, under controlled conditions, for a fraction of the DEXA cost. The segmental data tells you more than just total lean mass — it shows whether lean mass is staying in your legs while you lose body fat, or whether muscle loss is happening preferentially in one limb. That's data you can use to adjust training within a block.
And because the InBody offset is systematic rather than random, change over time is accurate even if the absolute number is 3% off. If you go from 23% body fat to 19% on InBody across 16 weeks, you've lost approximately 4% body fat. The absolute number may read 23% when DEXA would read 26%, but the direction and magnitude of change are real.
What disrupts InBody accuracy is protocol — specifically hydration. Scan post-workout, dehydrated, and the lean mass reading will spike artificially (less water resistance = looks more muscular). Scan overfed and overhydrated and fat reads higher. Consistent scan protocol matters: same time of day, fasted 3-4 hours, no exercise 12 hours prior, same clothing.
We run InBody every two weeks at Arzadon, same conditions every time. The trend line is what we're managing — not any single data point.
The Comparison Nobody Talks About: Visceral Fat
DEXA gives you regional fat — trunk versus limbs. But it can't separate visceral fat (the metabolically dangerous fat around your organs) from subcutaneous fat (the fat under your skin).
InBody 770 can. The 770 uses a proprietary algorithm to estimate visceral fat area in cm², with clinical validation comparing against abdominal CT scan. It's not as precise as an MRI, but it tracks visceral fat changes directionally — which is exactly what a fat loss coaching program needs.
Visceral fat responds faster to training and nutrition changes than subcutaneous fat. In executive clients we see visceral fat area drop meaningfully in the first 8 weeks, even when scale weight hasn't moved much. That's motivating data that DEXA simply doesn't provide.
The Coaching Decision
For clients starting a new program: consider a DEXA scan as the reference baseline, then track bi-weekly with InBody. You get absolute accuracy once, then track relative change cheaply and frequently. If budget is a constraint, InBody alone is sufficient — just use it consistently and don't compare your readings to DEXA-based population norms.
For ongoing program management: InBody wins. Segmental lean mass data, visceral fat tracking, bi-weekly scan frequency, and trend-line analysis give more actionable coaching information than a quarterly DEXA snapshot.
For post-program confirmation: DEXA provides a clean endpoint measurement you can compare back to the reference baseline without worrying about device-switching noise.
The question isn't which scan is better. It's which scan solves the problem you actually have.
What Arzadon Tracks and Why
We run InBody 770 bi-weekly on all coaching clients. The data we're watching: skeletal muscle mass, body fat percentage trend, visceral fat area, and segmental lean mass — particularly leg lean mass, which is the first thing to drop under caloric restriction if training isn't protecting it.
Every scan is run under the same protocol: morning appointment, 3-4 hours fasted, no training the morning of. We log the conditions alongside the result so if something looks anomalous, we can rule out protocol error before adjusting nutrition or training.
If a client wants a DEXA for an absolute baseline, we can refer them to one of two clinical facilities in Toronto that run research-grade scans. We'll take their DEXA report and build the InBody offset into their tracking model so the trend lines align.
The 4% gap between the two devices is a fixed offset you account for, not a problem you solve.
FAQ
Which is more accurate for body fat percentage? DEXA is more accurate for absolute body fat percentage. It's the clinical reference standard, with a test-retest precision of ±1-2%. InBody 770 reads 2-4% lower than DEXA on average, with variability depending on individual body type, hydration, and age.
Can I use InBody to track progress without ever doing a DEXA? Yes. For tracking change over time, InBody is sufficient — and arguably better, because you can scan frequently enough to catch plateaus early. The key is scanning under identical conditions every time. Trend direction and magnitude are reliable; just don't compare your readings to DEXA-based population norms.
What throws off an InBody scan? Hydration is the main variable. Dehydration raises lean mass readings artificially; overhydration does the opposite. Food, alcohol, and exercise in the 12 hours before a scan also affect results. We run InBody in the morning, fasted 3-4 hours, no training that morning. Same conditions every scan.
How often should I get scanned? For active clients in a 16-week fat loss or muscle building program, we scan bi-weekly. That's frequent enough to catch muscle loss early and adjust before it compounds. For maintenance clients or general health tracking, monthly is sufficient.
Does InBody measure visceral fat? The InBody 770 estimates visceral fat area in cm² using a validated algorithm compared against abdominal CT. It's not as precise as MRI, but it tracks visceral fat change directionally — which is what matters for coaching. DEXA cannot separate visceral from subcutaneous fat.
