:
Ab
PROGRESS IN ATOMIC MEDICINE —
ae
of cyclopropane in the gas phase of the system wasfollowed to equilibri-
um. From this. the amount of gas taken up by the body is calculated.
If the relative solubility of the gas in lipid and tissues is known then an
estimate of total body fat can be made.
In man. the rate of change of the concentration of the gas was not '
followed to equilibrium because the time required was in excess of 8
hours. This made it necessary to extrapolate mathematically to an equi.
,
librium value.
The following formulae have been used to estimate body fat. These
formulae have been evaluated by Keys and Brozek,** Siri,** and
Behnke.” In each instance, f represents the fat content as a’fraction of
the body weight.
ki —- ke
(ly) f= ae
where d = body density
.
TBW
(2) f = 1— ——
|
total body water
where TBW = —-———-—_—_
ka
M(body weight)
ks
:
k:
;
(4) £ = ——— ks ECW — ko
d
(5)
f
.
;
extracellular water
where ECW = ———_—___—
M
= kis ECW -— kit TBW ~- kis
K
(6) f = 1 — —
kes
ity) f—2l—m— ki K
Oo
(8)
M
f
=
1
a
K = total body potassium
\I = mineral mass
kas TBW — ki K
The second class of methods for calculating body fat are based on
one or more of the following.measurements; body density, body water,
extracellular fluid measurement. and total potassium. In principle, the
methods based upon body water depend upon an assumed constant
hydration of the nonfat portion of the body. The body density methods
depend upon an assumption of a two-compartment system: one of high
density, the hydrated Jean tissues (d = 1.10}. and one of low density
(d = 0.90). the fat compartment.’” The use of combined measurements
of body water and body density. in essence. takes into account the contri-