What Dietitians Actually Read on a Body-Composition Analyzer

A bioelectrical impedance (BIA) printout looks intimidating: a column of numbers, percentages and indices. Patients ask me which one is "the" number. The honest answer is that I read a few carefully and ignore several entirely.

Fat-free mass is where I start, because preserving it is usually the point of the intervention. Total body water tells me about hydration and oedema, which can otherwise make weight misleading. Phase angle — a raw electrical measure — is a quietly powerful marker of cell integrity and nutritional status that I watch over time.

What I do not over-read is a single absolute body-fat percentage to one decimal place, as if BIA were a DEXA scanner. It is not. Its strength is tracking change on the same device under the same conditions, not delivering a definitive one-off body-fat figure.

Used that way — same machine, same prep, repeated over weeks — BIA earns its place in a nutrition clinic. Used as a magic body-fat oracle, it disappoints.

How BIA fits alongside scales, stadiometers and the rest of the assessment kit is laid out in the clinical anthropometric equipment guide.