Because carotenes can be cleaved not only in the intestinal mucosa but also in other tissues (22), it has been suggested that
increased b-carotene intake can raise tissue retinol concentrations without raising concentrations of retinol and b-carotene in serum. In this case, serum retinol concentrations could not be used to estimate apparent conversion factors. However, this is an unlikely explanation for the results reported in this study. If serum concentrations of retinol and b-carotene increase after one source of provitamin A carotenoids is consumed, they should also increase after another source is consumed because the intestinal mucosa would be unable to distinguish between bcarotene of different origins.