Is Your Body Scan Lying?

Is Your Body Scan Lying?

InBody and DEXA scans are supposed to be the most objective way to track body composition. But just like with measuring your bodyweight, there are ways the data can lead you astray.

Has this ever happened to you or someone you know? -Get a scan -Freak out -Change your entire program -Get scanned again -Assume that nothing's working

It might be that your program is working fine - you just got scanned too quickly to give your body a chance to adapt.

​Why the Number Bounces Around? InBody scans use bioelectrical impedance, sending a small electrical current through your body to estimate composition based on how well that current moves through your tissue. Water conducts that current well, so the more hydrated you are, the higher your lean mass tends to read and the lower your body fat percentage tends to read. Dehydrated, it's the reverse.

That means two scans 48 hours apart can show a real difference in body fat percentage without a pound of actual fat changing. Your hydration was just different on test day.

DEXA scans are less prone to this, since they measure bone and tissue density directly rather than inferring composition from an electrical signal. But they also cost more and aren't as accessible, which honestly works in your favour. It removes the temptation to test every week just because you can.

Either way, treat a single scan as a snapshot, not a verdict. What matters is the trend over multiple scans spaced far enough apart for real change to happen, about once every 8 to 12 weeks for most people. Muscle and fat just don't shift meaningfully in a week or two.

How To Get More Accurate Results A few things help a lot:

Test at the same time of day, ideally first thing in the morning before eating or drinking.

Skip hard workouts in the 24 hours before, since exercise shifts fluid and can throw off the reading.

Avoid sauna, hot tub, or a hot shower right before testing, same reason.

Watch your sodium the day before. More sodium means more water retention, which skews results.

If you have a menstrual cycle, hormonal shifts affect water retention significantly. Try to test at a similar point each cycle for comparable results.

Even with DEXA's added reliability, I'd stick to that same 8 to 12 week window, because more data isn't always better.

What Over-Testing Actually Costs You The bigger issue isn't wasted time or money, it's what people do with a bad data point. Body fat ticks up on a noisy reading, and the instinct is to panic. Cut calories further, add more cardio, abandon a program that was actually working.

The noise cuts both ways too. A reading that comes back better than expected is arguably more dangerous, because nobody questions good news. You walk away crediting whatever you happened to be doing that week and commit harder to something that may have had nothing to do with it. Either way, every change you make based on noise resets the clock on knowing whether anything actually works.

There's a mental cost here too, and I think it gets underestimated. Testing constantly turns training into something you're graded on every few days. That's exhausting, and it makes people far more likely to quit something that was working than to stick with it long enough to see results.

What to Log Daily, What to Test Rarely The simplest way to think about this is to separate what you're doing from what you're building.

Calories, steps, sleep, and your training sessions are inputs. They're choices you make every day, and logging them daily is how you know whether you're actually executing the plan. Bodyweight sits alongside them, not because any single reading means much, but because a weekly average smooths out the fluctuation and shows you the direction things are heading.

Body fat percentage and max lifts are outcomes. They're the result of months of those daily inputs stacking up, and they need real time to move. Testing them constantly doesn't give you feedback, it gives you noise dressed up as feedback. Save your max lifts for planned testing blocks and your body composition scans for scheduled dates on the calendar.

Log what you're doing every day - test what you're building on a schedule. 💪