⁴⁰ K measurement

The ⁴⁰ K measurement is a method for indirectly measuring the body fat percentage in living people.

Naturally occurring potassium consists of 0.012% of the radioactive isotope ⁴⁰ K. ⁴⁰ K emits gamma radiation with an energy of 1.46 MeV when it decays . Most of this escapes from the body and can therefore be measured non-invasively outside the body with a gamma detector.

Potassium ingested with food is not evenly distributed throughout the body; the potassium concentration in adipose tissue is lower than in the rest of the body. Thus, the concentration of the radioactive isotope in adipose tissue is also lower.

The ⁴⁰ K activity per kilogram of body mass is determined with a particle detector that encloses the entire body as far as possible ( whole body counter ) . It is used to determine the potassium content averaged over the entire body. The higher the activity per kg, i.e. the higher the potassium content, the smaller the fat content. Using tables, you can determine the body fat percentage from the ⁴⁰ K activity per kg.

• Advantage: With this measuring method you can not only work close to normal weight, but also cover the entire range from extremely high to extremely low body fat percentage.

• Disadvantage: There are very few facilities that operate such measuring devices.