ZINC-ABSORPTION ESTIMATED BY FECAL MONITORING OF ZINC STABLE ISOTOPESVALIDATED BY COMPARISON WITH WHOLE-BODY RETENTION OF ZINC RADIOISOTOPES IN HUMANS

Knowledge about zinc availability from human diets is limited due to m ethodological difficulties. Recently developed stable isotope techniqu es for estimating dietary zinc absorption were compared with radioisot ope techniques in five men and three women. Stable and radioactive zin c isotopes were simultaneously administered. Fecal excretion of the is otopes as well as whole-body retention of the radioactive zinc isotope was monitored. Concentration of stable zinc isotope label in fecal sa mples was determined by inductively coupled plasma mass spectrometry b y fully quantitative measurements and from inductively coupled plasma mass spectrometry isotope ratios combined with analysis of total zinc content using atomic absorption spectrometry. Zinc absorption estimate d from whole-body retention was 27 +/- 6% ((x) over bar +/- SD), estim ated zinc absorption obtained by fecal monitoring of radioisotope was 26 +/- 9%, and the two stable zinc measurements resulted in values of 29 +/- 12 and 33 +/- 12%, respectively. There was no significant diffe rence in zinc absorption estimated from whole-body retention and with the fecal monitoring methods. Recovered stable zinc isotope label was significantly lower than recovered radioisotope. For individual fecal samples, systematic differences of 16% and 12%, respectively (P < 0.05 ), between the radioisotope recovery and the recovery of stable isotop es with the two methods for measurement was observed. The stable zinc isotope technique for measurement of zinc absorption resulted in mean results similar to those of the radioisotope technique, but with a lar ger variation in the measurements.