AJP - Regulatory, Integrative and Comparative Physiology, Vol 260, Issue 3 627-R634, Copyright © 1991 by American Physiological Society
Water hydrogen incorporation into body fat in pigs: effect on double/triple-labeled water method
P. Haggarty, B. A. McGaw, M. F. Fuller, S. L. Christie and W. W. Wong
Rowett Research Institute, Bucksburn, Aberdeen, United Kingdom.
A basic assumption of the doubly labeled water (DLW) and triply labeled
water (TLW) methods for measuring water flux (rH2O), CO2 production (rCO2),
and fractionated water loss (X) is that the H of body water only leaves the
body as water. Any loss of isotopes in other products will introduce an
error into these techniques. The body fat represents the largest potential
sink for water H. 2H sequestration into the carcass fatty acids was
investigated in eight pigs labeled with 2H2O for 21 days. rCO2 was measured
simultaneously in respiration chambers to allow an accurate assessment of
the effect of 2H sequestration on the estimated rCO2. The fat content of
the diet (1.63%), level of intake, and stage of maturity were all designed
to give the widest possible range of sequestration effects. Four animals
were restricted to their estimated maintenance requirement and four were
allowed to feed ad libitum giving a range of weight gain from 100 to 650
g/day. This was reflected in the estimated error on rH2O (+0.42% in the
restricted group and +2.52% in the fast-growing animals) and on rCO2 (-1.30
and -7.59%, respectively). The error on the calculation of X using TLW was
+0.03 units in the restricted group and +0.20 units in the fast-growing
animals. The error of +0.2 on X propagates through to an underestimate of
rCO2 of approximately 4%, and since this is additive with the error on DLW
the ultimate error on rCO2 using TLW would be approximately -12%.(ABSTRACT
TRUNCATED AT 250 WORDS)
