Jones Martina L, Treloar Tony, Nixon Peter F
Department of Biochemistry and Molecular Biology, The University of Queensland, St Lucia, Queensland 4072, Australia.
J Nutr. 2003 Feb;133(2):489-95. doi: 10.1093/jn/133.2.489.
The newborns of mammals have a high folate demand, yet obtain adequate folate nutrition solely from their mothers' milk despite its low folate content. Milk folate is entirely bound by an excess of folate-binding protein (FBP), prompting speculation that FBP may affect the bioavailability of the limited folate supply. Previous research has shown that FBP-bound folic acid is more gradually absorbed, thereby reducing the peak plasma folate concentration and preventing loss into the urine. Natural folates are reduced derivatives of folic acid, with milk predominantly containing 5-methyltetrahydrofolate, yet little research has been carried out to determine the role of FBP in the bioavailability of reduced folates. We studied the effect of FBP on folate nutrition of rats in both single-dose and 4-wk feeding experiments. The effect of FBP was influenced by the presence of other milk components. FBP increased bioavailability of dietary folate when it was consumed with other whey proteins or with soluble casein. However, in the presence of acid-precipitated casein or a whey preparation enriched in lipids, bioavailability was decreased. These results highlight the difficulties of extrapolating from experimental results obtained using purified diets alone and of studying interactions among dietary components. They suggest that the addition of FBP-rich foods to folate-rich foods could enhance the bioavailability of natural folates, but that the outcome of such a combination would depend on interactions with other components of the diet.
哺乳动物的新生儿对叶酸的需求量很高，然而尽管母乳中的叶酸含量很低，但它们仅从母乳中就能获得充足的叶酸营养。母乳中的叶酸完全与过量的叶酸结合蛋白（FBP）结合，这引发了人们的猜测，即FBP可能会影响有限叶酸供应的生物利用度。先前的研究表明，与FBP结合的叶酸吸收更为缓慢，从而降低了血浆叶酸浓度峰值，并防止其随尿液流失。天然叶酸是叶酸的还原衍生物，母乳中主要含有5-甲基四氢叶酸，但关于FBP在还原型叶酸生物利用度中的作用，目前开展的研究很少。我们在单剂量和4周喂养实验中研究了FBP对大鼠叶酸营养的影响。FBP的作用受到其他母乳成分的影响。当FBP与其他乳清蛋白或可溶性酪蛋白一起食用时，它会提高膳食叶酸的生物利用度。然而，在存在酸沉淀酪蛋白或富含脂质的乳清制剂的情况下，生物利用度会降低。这些结果凸显了仅根据使用纯化饮食获得的实验结果进行推断以及研究膳食成分之间相互作用的困难。它们表明，在富含叶酸的食物中添加富含FBP的食物可能会提高天然叶酸的生物利用度，但这种组合的结果将取决于与饮食中其他成分的相互作用。
