Body Composition 27mined by densitometry correlates well with excreted
3-methylhistidine. The chemical determination of
3-methylhistidine is, however, more complicated
than that of creatinine. A unique feature of 3-
methylhistidine is that it gives a measure of muscle
protein breakdown. Given the greater expense of
measuring 3-methylhistidine and the limited benefi t
for muscle mass estimates, it is probably best to use
it primarily for turnover studies.
The main disadvantages of creatinine and 3-
methylhistidine excretion as measures for body com-
position are the large variability in excretion, the
necessity to follow a controlled (meat-free) diet for
several days before and during the urine collections,
and the diffi culties associated with collecting 24 hour
urine samples.
Use and misuse of body composition data
Information on the body composition of groups of
subjects or individuals is important, as body compo-
sition is an indicator of nutritional status and also
provides information about acute water homeostasis.
Depending on what information is needed, several
methods are available. However, all have their advan-
tages and limitations. The price of the method
(both the instrument and the required personnel), the
eventual stress and danger (e.g., radiation) for the
subject, and the time necessary to obtain the informa-
tion determine the choice of the method, as well as
the required accuracy. The use in epidemiological
studies is different than that in clinical situations or
in physiological research. Table 2.7 provides a “buyer’s
guide” to the several methods discussed in this
chapter. It is diffi cult to generalize as to which method
should be used in a given study. Apart from the
factors mentioned in Table 2.7, availability plays
an important role. Some situations are discussed
below.
For the description of body fatness of a large general
population group, the calculation of the body fat per-
centage from the BMI may be as good as or even
better than the more expensive information obtained
from bioelectrical impedance or the laborious mea-
surement of skinfold thicknesses. Whichever method
is to be used for the prediction of body fat percentage
in the population, it is important to remember that
the formulae used should have been validated in the
population under study. The fact that a formula is
cross-validated by the authors who published the
formula does not mean that the formula is valid in
another population. The use of the Durnin and
Womersley (1974) equations for estimating body fat
from the sum of four skinfolds may be correct if the
population is adult but younger than about 60 years.
In older subjects, the amount of body fat is likely to
be underestimated with these formulae. Therefore,
their use and thoughtless interpretation in the elderly
would lead to completely wrong conclusions aboutTable 2.7 Buyer’s guide to different methods used to determine body composition
Method Accuracy Expenses Radiation Time Convenience for subject
Carcass analysis + + + − −
Neutron activation + + + − −− − + ++ +
Densitometry + + + + + +/−
Dilution method + + +/− (−) ++
(^40) K method + + − + ++ +
DXA + + + +/− − + ++ +
More-compartment models + + + −− −+
CT scanning +^ + − − − +^ ++^ +
MRI scanning +^ + − +^ + +
Anthropometry + +^ +^ ++^ + +
Infrared interactance + + ++ ++ +
Bioelectrical impedance ++ + + ++ + + +
TOBEC +− + ++ +
Creatinine/N-methylhistidine excretion ++ −−
DXA, dual-energy X-ray absorptiometry; CT, computed tomography; MRI, magnetic resonance imaging; TOBEC, total body electrical
conductivity.
- +, excellent; + +, very good; +, good; +/–, reasonable; –, bad; – –, very bad.