How to read an InBody printout

An InBody sheet is a bioelectrical impedance result: the device passes a small current through the body and estimates its composition from the reading. The sheet prints segmental readings, phase angle and a score out of a hundred. Four lines hold the numbers the rest are built on.

From those you can work out two figures the sheet often buries: lean mass, which is weight minus fat mass, and FFMI, which is lean mass adjusted for height.

What FFMI adds

Bodyweight says nothing about how much of it is lean. Fat-free mass index divides lean mass in kilograms by height in metres squared, so two people of different heights can be compared. Kouri and colleagues added a small correction that normalises the value to a height of 1.8 m^[1].

In their sample of 157 male athletes, the normalised FFMI of those who had not used anabolic steroids extended up to a well-defined limit of 25.0^[1].

The ESPEN guideline on impedance asks for follow-up measurements at the same time of day, under standardised conditions.

How to make two scans comparable

The European Society for Clinical Nutrition and Metabolism lists the conditions that change an impedance reading^[2].

• Same device and the same time of day for every follow-up; each device applies its own prediction equation^[2].
• Fasted: the guideline names fed or fasting state as what affects results most^[2].
• Bladder voided before the measurement^[2].
• No exercise beforehand: straight after exercise resistance fell by about 3 per cent and reactance by about 8 per cent, back to normal an hour later^[2].

The sheet prints numbers whatever the conditions were. A scan taken fed, or straight after training, is not the same measurement as one taken under the standard conditions, and the two should not be read as a change.

Reading the trend

Two scans make a line; three start a trend. Because the sheet lists fat mass and skeletal muscle mass separately, a change in weight between scans can be split into the part that is fat and the part that is not. The ESPEN guideline notes that follow-up by impedance is possible in people without abnormal hydration, but must be interpreted with caution^[2]. QuietGains keeps each scan in a body composition history.

What the score out of a hundred is for

The score is the manufacturer’s own summary figure, not a measurement. None of the sources below describe it, so this piece reads the four lines it sits beside instead.