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Serum retinol δ13C‰ plotted against liver VA δ13C‰ for gerbils that consumed diets with varying amounts and sources of provitamin A carotenoids and preformed VA. Only gerbils with values for both outcomes are plotted (n = 40; 3–7/group) along with the best fit line of the data (solid line) and y = x (dashed line). VA, vitamin A.
