By: Gerald Ernat
When it comes to tracking health or fitness progress, the number on the scale doesn’t tell the whole story. Two people can weigh the same but look completely different depending on how much muscle, fat, and bone they have. That’s why measuring body composition—the breakdown of fat mass and lean mass—is so valuable.
Below, you’ll find the most common ways to measure body composition, what each method does well, and what to keep in mind when using them.
Bioelectrical Impedance Analysis (BIA)
Many smart scales and devices like the InBody machine use BIA. A very small electrical current is sent through your body, and the device estimates your body fat and muscle mass based on how easily the current travels. As a Sports Dietitian for the military, I use this method daily to measure Soldiers and help them move toward their physique goals.
Research Spotlight:
A study led by Dr. Grant Tinsley found that simply drinking water or standing for a while before testing could change BIA results, sometimes making body fat appear higher even though nothing about your body changed.
DEXA Scan
DEXA uses low-dose X-rays to separate fat, lean tissue, and bone. It’s considered one of the most accurate ways to measure body composition.
Skinfold Calipers
A trained professional pinches and measures fat at several points on your body, then uses those numbers to estimate body fat percentage.
Circumference Measurements
This includes waist, hip, and neck measurements, or waist-to-height ratios (commonly used by the military). It’s a simple way to estimate health risks related to fat storage.
BOD POD (Air Displacement)
You sit in a small pod that measures how much air your body displaces to estimate your body fat percentage.
Hydrostatic (Underwater) Weighing
You’re submerged in water, and your body density is calculated based on how much water you displace.
Progress Pictures
Sometimes the simplest tool can be the most powerful. Taking photos of yourself regularly—from the front, side, and back—can reveal changes numbers miss.
Tip: Take photos in consistent lighting, with similar clothing, and at the same time of day (morning is best) to get the clearest view of changes over time.
The Big Picture: What Really Matters
Any method can be influenced or manipulated. Drinking water, eating a big meal, wearing heavy clothes, or testing at different times of day can all change results. A single number or photo only gives you a snapshot of where you are right now. What matters most is consistency: test under the same conditions every time (morning is ideal), wear similar clothing, go to the bathroom first, use the same method or device, and take pictures in the same spot with similar lighting. Following these habits lets you see trends over time, whether you are losing fat, gaining muscle, or maintaining, without obsessing over one reading that might be off.
Stressing over a single number or photo only adds confusion. Tracking trends, measuring consistently, and being patient will give you the most accurate view of your progress.
Whether you're trying to lose fat, build muscle, or just feel more in control of your diet, I’ll help you build a plan around your goals, preferences, and lifestyle. No rigid rules. No shame. Just clear, science-backed guidance and support.
If you're ready to take the guesswork out of your nutrition, I’d love to work with you.
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