InBody, Scale or DEXA: Which Body Number to Trust
What the bathroom scale, an InBody 580 scan and a DEXA each measure, where each one misleads, and how Austin clients use them together to track progress.
Three tools claim to tell you how your body is changing, and they disagree with each other constantly. Understanding what each one actually measures is the difference between adjusting a plan for a real reason and adjusting it because of water weight.
The bathroom scale
It measures one thing: total mass, including bone, organs, muscle, fat, glycogen, food in transit and — the big one — water. Day-to-day swings of two to four pounds are normal and almost entirely fluid. A salty dinner, a hard leg session, a short night of sleep or the start of a menstrual cycle each move it. The scale is genuinely useful as a weekly average, and close to useless as a single morning reading. Its blind spot is fatal for weight care: it cannot tell fat loss from muscle loss.
InBody 580 (bioelectrical impedance)
The InBody sends small currents through the body and infers tissue composition from how they conduct. It reports fat mass, skeletal muscle mass, segmental balance between limbs and trunk, visceral fat area and hydration. Its strength is repeatability and speed: about sixty seconds, no radiation, easy to run every four to eight weeks. Its limitation is that hydration status shifts the reading, so the absolute body-fat percentage on any single scan carries a margin of error.
The practical fix is standardizing conditions — same time of day, before eating, before training, similar fluid intake — and reading the trend across scans rather than obsessing over one number. Done that way, the InBody is the best tool most people have for answering "is the weight I am losing coming from fat?" We run it at both the West Lake Hills and Hutto clinics; details are on our body composition analysis page.
DEXA
A DEXA scan uses low-dose X-ray to distinguish bone, lean tissue and fat, and it is the closest thing to a reference standard available outside a research lab. It also reports bone mineral density, which nothing else here does. The trade-offs are cost, a small radiation dose, a scheduled appointment at an imaging facility, and the fact that different machines are not perfectly comparable. Most people do not need one every quarter; one baseline, or a scan when bone density is the actual question, does the job.
How to use all three
- Weigh daily, read weekly. Average seven mornings and compare averages, never single days.
- Scan every four to eight weeks. Same conditions each time. Watch fat mass and skeletal muscle mass separately.
- Add a DEXA when the question warrants it. Bone density, an athletic baseline, or a composition number you want anchored precisely.
- Keep the non-machine measures. Waist circumference, working weights in the gym, how clothes fit, and energy through the afternoon. When these all agree, no scan is going to overturn them.
Where measurement fits in a plan
Composition answers what is changing, but not why. When the direction is wrong, a resting metabolic rate breath test explains the energy side and lab work explains the physiology; the sequence we use is laid out in what to measure before you start. If muscle protection is the priority, losing fat without losing muscle covers the levers that move those two lines apart.
Clients travel to our clinics from Rollingwood, Bee Cave, Lakeway, central Austin, Round Rock, Pflugerville and Georgetown for scans and metabolic testing, then work with a coach virtually between visits. Browse the full menu on wellness testing and assessments, pair it with the plans on Austin weight loss coaching, and check pre-tax payment options in our HSA/FSA guide.
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