Measurement of deuterium oxide by infrared spectroscopy and isotope ratio mass spectrometry for quantifying daily milk intake in breastfed infants and maternal body fat.

Measurements of deuterium oxide concentrations (DOC) in saliva by infrared spectroscopy (IRS) and isotope ratio mass spectrometry (IRMS) were compared for the calculation of infants' milk intake and maternal body fat. Deuterium oxide (30 g) was given to the mother. DOC by IRS and IRMS were 340 +/- 209 and 345 +/- 202 ppm. The mean difference between both methods (4.62 +/- 76.3) was not different from zero (p = .57). Bland and Altman analysis showed no significant overall bias (r = 0.10; p = .33), but dispersion within the limits of agreement. The mean milk intake in the infants' by IRS and IRMS were 624 +/- 296 g/day and 634 +/- 327 g/day (p = .642) and the mothers' mean body fat were 31.3 +/- 12% and 31.5 +/- 13% (p = .755). The results appear to be the same for milk intake and body fat by the two methods and no evidence of bias was found.