The effect of food preparation on the bioavailability of carotenoids from carrots using intrinsic labelling

A strategy to reduce the incidence of vitamin A deficiency is to improve precursor bioavailability from meals. Since vitamin A precursors are fat-soluble, we noted that carotenoids are more easily absorbed from food if prepared in such a way that the food matrix containing provitamin A (beta-carotene) is sufficiently fat rich. To quantify this effect, we have developed a stable isotope methodology. By regular watering with H-2-labelled water, we were able to produce several kg of intrinsically labelled carrots, with carotenoids labelled to 0.63% excess H-2. These were divided into 100 g portions and fed to a small group of healthy subjects both raw and stir-fried. To normalise for inter-individual variation in absorption and subsequent metabolism, small quantities of extrinsically C-13-labelled beta-carotene and H-2-labelled retinol acetate were also incorporated into the meal. After ingestion of the carrots, blood lipids were monitored for a period of 3 d in order to determine the kinetics of beta-carotene and retinol. From kinetic data, it was estimated that the bioavailability of carrot-derived beta-carotene compared with pure beta-carotene was about 11% for raw carrots, but 75% when the carrots were stir-fried. Conversely, there was a slight reduction in the bioconversion to retinol from beta-carotene when the latter was derived from the stir-fried meal compared with that from raw carrots. When these two factors are combined, the yield of retinol from the carotene in carrots was found to be enhanced by a factor of 6.5 by stir-frying.