Jacob R A, Pianalto F S, Henning S M, Zhang J Z, Swendseid M E
Western Human Nutrition Research Center, U.S. Department of Agriculture, Presidio of San Francisco, CA 94129, USA.
J Nutr. 1995 Jun;125(6):1495-502. doi: 10.1093/jn/125.6.1495.
Ten healthy adult men were fed a diet low in folate and exogenous methyl groups to study the effects on in vivo methylation capability. The men were housed in a metabolic unit for the entire 108 d of the study. After a 9-d baseline period (Period 1), the men were fed a soy-product-amino acid defined diet for 45 d, which provided 25 micrograms/d of folate for 30 d (Period 2) and, with a folate supplement, 99 micrograms/d for 15 d (Period 3). During Period 2 and Period 3, the low methionine and choline diet was supplemented with methionine for half the subjects to vary the dietary methyl group intake. The periods were then repeated over the next 54 d (Periods 4-6), with a crossover of methionine intakes in Period 5 and Period 6. A 1-g oral dose of nicotinamide was given at the end of each period and methylated urine metabolites determined. Other measures related to in vivo methylation capability included urine creatinine, and plasma and urine carnitine. Even with moderate folate depletion, none of these measures was decreased by low methionine and choline intakes. Plasma methionine concentrations were unchanged throughout. Limiting exogenous methyl group intake by restricting dietary methionine and choline did not impair in vivo methylation capabilities for the variables tested, even at low folate intake.
选取10名健康成年男性，给予低叶酸和外源性甲基饮食，以研究其对体内甲基化能力的影响。在为期108天的研究中，这些男性被安置在代谢单元中。经过9天的基线期（第1阶段）后，这些男性食用一种由大豆制品和氨基酸组成的特定饮食，为期45天，其中30天提供25微克/天的叶酸（第2阶段），并在补充叶酸后，连续15天提供99微克/天的叶酸（第3阶段）。在第2阶段和第3阶段，对于一半的受试者，在低蛋氨酸和胆碱饮食中补充蛋氨酸，以改变膳食甲基摄入量。然后在接下来的54天内重复这些阶段（第4 - 6阶段），在第5阶段和第6阶段交叉摄入蛋氨酸。在每个阶段结束时给予1克口服烟酰胺，并测定甲基化尿液代谢物。其他与体内甲基化能力相关的指标包括尿肌酐、血浆和尿肉碱。即使存在中度叶酸缺乏，低蛋氨酸和胆碱摄入量也不会使这些指标降低。血浆蛋氨酸浓度在整个过程中保持不变。通过限制膳食蛋氨酸和胆碱来限制外源性甲基摄入量，即使在低叶酸摄入情况下，也不会损害所测试变量的体内甲基化能力。
