The Number on the Body-Fat Scale

体脂秤上的数字

Place · Level 3 · Measurement

Connected to · 1

contrast · 1

Weight Management · Foundations
BMI cannot separate muscle from fat, so people reach for body-fat percentage instead — but that number carries its own 15-20 point uncertainty band. Neither settles the question alone; waist and other signals have to come in.

它测的不是脂肪

Stop 1/5

It does not measure fat

You step on, and it reads 22.4%. One decimal place. It looks like a measurement.

It is not a measurement. It is an inference.

A body-fat scale does exactly one thing: it passes a very small current up through your feet (and, on models with handles, your hands too) and measures how much resistance that current meets on the way. That resistance is called impedance.

It is not measuring fat. It is measuring how easily electricity travels.

And how easily electricity travels through you depends mostly on water. Muscle, blood, and organs are water-rich and conduct well; fat holds little water and conducts poorly. So the raw datum a body-fat scale actually obtains is a number tightly related to how much water is in you.

Between that number and the 22.4% on the display sit two more inference steps — and fat itself is never measured, not even once.

Read story

Educational content, not medical advice — consult a clinician.

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The Number on the Body-Fat Scale

体脂秤上的数字

Place · Level 3 · Measurement

Connected to · 1

contrast · 1

Weight Management · Foundations
BMI cannot separate muscle from fat, so people reach for body-fat percentage instead — but that number carries its own 15-20 point uncertainty band. Neither settles the question alone; waist and other signals have to come in.

它测的不是脂肪

Stop 1/5

It does not measure fat

You step on, and it reads 22.4%. One decimal place. It looks like a measurement.

It is not a measurement. It is an inference.

A body-fat scale does exactly one thing: it passes a very small current up through your feet (and, on models with handles, your hands too) and measures how much resistance that current meets on the way. That resistance is called impedance.

It is not measuring fat. It is measuring how easily electricity travels.

And how easily electricity travels through you depends mostly on water. Muscle, blood, and organs are water-rich and conduct well; fat holds little water and conducts poorly. So the raw datum a body-fat scale actually obtains is a number tightly related to how much water is in you.

Between that number and the 22.4% on the display sit two more inference steps — and fat itself is never measured, not even once.

Read story

Educational content, not medical advice — consult a clinician.