EVALUATION OF INTESTINAL ABSORPTION OF BETA-CAROTENE

许多营养癌症研究表明，β-胡萝卜素 (BC)，因为它具有抗氧化活性，不依赖于其 维生素A原的特性在预防某些疾病方面很重要 癌症。由于BC摄入补充剂量或甚至过量剂量 显然不会造成维生素A(VA)毒性，使用BC 已经被NCI考虑进行化学预防试验，以减少 高危人群中某些癌症的发病率。在 在过去的两年里，我们正在进行的NCI支持的项目表明 完整BC的吸收以及BC在肠道内转化为VA 在不同的学科中有很大的不同。广泛的BC吸收 通过测量以下患者的血清BC反应来确定试验 摄取不同剂量的BC-VA与不同数量的食物 在年轻和年长的受试者中，有几个因素表明影响 BC的肠道吸收。这些因素包括BC的剂量， 卡路里总量，食物供应方式， 脂肪吸收率与年龄和身体组成 研究对象。然而，对肠道的深入量化 人体的吸收受到阻碍，因为缺乏 适合和安全的BC同位素化合物。最近，有一种方法可以 膳食成分净吸入量的测量 已经描述了一天内的补充剂。此方法(总计 肠道冲洗)包括用以下物质清洁胃肠道 试餐前后的一种特殊溶液。随后， 测定直肠流出物中的常量和微量营养素。这 该方法避免了同位素固有的一些困难 学习。运用这一方法，本研究旨在评估 BC和常量营养素的消化道净消失率，当 BC(15毫克)或安慰剂与美国人的常规饮食一起服用。 最初，年轻(18-25岁)和老年(65-75岁)的男性将接受筛查 16例肠道正常者呼气氢气试验结果分析 弗洛拉。然后在每个受试者中，空肠菌群和网 消化道内源性大量营养素、维甲酸和 类胡萝卜素将被测量。随后，以随机的方式， 每名受试者将参加为期4周的8个实验 测试之间的间隔。这些实验将评估血清 BC或甘油三酯的浓度-时间曲线 安慰剂与各种饮食(500-1000千卡，25%-40%脂肪)一起服用 还将测量BC和BC的总肠道吸收 BC的排泄量。肠道菌群等因素的影响 此外，还将研究肠道转运时间对BC吸收的影响。 这项研究将首次为我们提供定量的 关于BC吸收的数据，并将帮助我们建立饮食 BC补充剂和化学预防试验指南。

Many nutrition-cancer studies have demonstrated that beta-carotene (BC) because of its anti-oxidant activity and independent from its provitamin A property is important in the prevention of certain cancers. Since BC intake in supplemental or even excess doses apparently does not cause vitamin A (VA) toxicity, the use of BC has been considered for chemoprevention trials by NCI to reduce the incidence of certain cancers among high risk populations. In the last 2 years, our ongoing NCI supported project has shown that the absorption of intact BC and also intestinal conversion of BC to VA are quite variable in different subjects. Extensive BC absorption tests as determined by measurement of serum BC response following ingestion of graded doses of BC VA are with various amounts of food in young and old subjects have shown that several factors influence intestinal absorption of BC. These factors include the dose of BC, the total amount of calories, the modality of food delivery, the rate of fat absorption and the age and body composition of the subjects. However, in depth quantification of intestinal absorption in humans has been hampered because of the lack of suitable and safe isotopic BC compounds. Recently, a method for the measurement of the net absorption of dietary constituents or supplements in a single day has been described. This method (total gut washout) consists of cleansing the gastrointestinal tract with a special solution before and after a test meal. Subsequently, the macro- and micronutrients in rectal effluent are measured. This method avoids some of the difficulties inherent with isotopic studies. Using this method the present study aims to evaluate the net alimentary tract disappearance of BC and macronutrients,when BC (15mg) or placebo is given with a regular American diet. Initially, young (18-25) and old (65-75) men will be screened with a breath hydrogen test to select 16 subjects with normal intestinal flora. Then in each subject, the jejunal flora and the net alimentary tract endogenous losses of macronutrients, retinoids and carotenoids will be measured. Subsequently, in a random manner, each subject will participate in 8 experiments with 4 week intervals between tests. These experiments will evaluate the serum concentration time curves of BC and triglycerides when BC or placebo are given with various diets (500-1000 Kcal, 25-40% fat) and will also measure the total intestinal absorption of BC and fecal loss of BC. The effect of factors such as intestinal flora and intestinal transit time on BC absorption will also be studied. This study will provide us for the first time with quantitative data on BC absorption and will help us in establishing dietary guidelines for BC supplementation and for chemopreventive trials.