Assessment of nutritional status in rhesus monkeys: comparison of dual-energy X-ray absorptiometry and stable isotope dilution.

Body composition estimates from dual-energy X-ray absorptiometry and stable isotope dilution ((2)H and (18)O) were compared in 61 rhesus monkeys (Macaca mulatta) from the ongoing long-term energy restriction study at the University of Wisconsin. Their average age was 18.9 +/- 2.5 y/o. Of the animals, 51% were in the energy restricted group and 38% were females. Although the correlation between methods was highly significant for fat mass (R(2) = 0.97, SEE = 0.25 kg or 7.5%, P < 0.0001) and fat-free mass (R(2) = 0.98, SEE = 0.29 kg or 3.6%, P < 0.0001), we observed that dual-energy X-ray absorptiometry underestimated fat mass by 0.67 +/- 0.26 kg (7.5%, P < 0.0001) and overestimated fat-free mass by 0.57 +/- 0.29 kg (20%, P < 0.0001) when compared with isotope dilution. Taken together with data from the literature, the present results emphasize the usefulness of dual-energy X-ray absorptiometry to derive body composition and thus nutritional status in monkeys, but demonstrate the importance of validation experiments for a given DXA model and software.