MRC Human Nutrition Research, Elsie Widdowson Laboratory, Fulbourn Road, Cambridge CB1 9NL, UK.
Br J Nutr. 2012 May;107(9):1350-66. doi: 10.1017/S000711451100451X. Epub 2011 Sep 19.
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 (β-carotene) is sufficiently fat rich. To quantify this effect, we have developed a stable isotope methodology. By regular watering with 2H-labelled water, we were able to produce several kg of intrinsically labelled carrots, with carotenoids labelled to 0.63 % excess 2H. 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 13C-labelled β-carotene and 2H-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 β-carotene and retinol. From kinetic data, it was estimated that the bioavailability of carrot-derived β-carotene compared with pure β-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 β-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.
减少维生素 A 缺乏症发生率的策略是提高膳食中维生素 A 前体物的生物利用度。由于维生素 A 前体物是脂溶性的，我们注意到，如果以食物基质中含有维生素 A 原（β-胡萝卜素）的方式来制备，类胡萝卜素从食物中吸收会更容易。为了量化这种效果，我们开发了一种稳定同位素方法。通过定期用 2H 标记水浇水，我们能够生产出几公斤内在标记的胡萝卜，其类胡萝卜素的 2H 标记量为 0.63%过剩。这些胡萝卜被分成 100 克的部分，分别喂给一小群健康受试者生吃和炒菜吃。为了使个体吸收和随后的代谢差异正常化，也将少量的外源性 13C 标记的β-胡萝卜素和 2H 标记的视黄醇乙酸酯纳入膳食中。摄入胡萝卜后，监测了 3 天的血脂，以确定 β-胡萝卜素和视黄醇的动力学。根据动力学数据，与纯β-胡萝卜素相比，生胡萝卜中胡萝卜素衍生的β-胡萝卜素的生物利用度约为 11%，而炒胡萝卜时则为 75%。相反，当β-胡萝卜素来自炒菜时，与来自生胡萝卜相比，其转化为视黄醇的生物转化率略有下降。当将这两个因素结合起来时，发现通过炒菜可以将胡萝卜中的类胡萝卜素转化为视黄醇的效率提高 6.5 倍。
