Zinc absorption in adult humans: The effect of protein sources added to liquid test meals

The influence of different protein sources on Zn absorption was evaluated in healthy adults by radioisotopic labelling of single meals, followed by whole-body retention measurements 14 d after intake. Semi-synthetic liquid diets were used for the evaluation of different animal-protein sources and dephytinized soyabean-protein isolate (< 0·01 g phytic acid/kg). Zn absorption was measured in the same subjects from identical test meals containing no added protein. No statistically significant differences were found in the Zn absorption from test meals containing bovine whey, casein or egg albumen when compared with test meals without added protein. Bovine serum albumin (BSA) and soyabean-protein isolate (< 0·01 g phytic acid/kg) significantly reduced the mean absorption of Zn from 45-49% (no added protein) to 38·0 (SD 10·9) (BSA, P < 0·05) and 339 (SD 12·6)% (soyabean-protein isolate < 0·01 g phytic acid/kg, P < 0·01). These results demonstrate that Zn absorption is inhibited by certain protein sources, such as BSA and dephytinized soyabean-protein isolate, while other proteins have little or no effect.