PLASMA-CONCENTRATIONS OF HOMOCYSTEINE AND OTHER AMINOTHIOL COMPOUNDS ARE RELATED TO FOOD-INTAKE IN HEALTHY-HUMAN SUBJECTS

We investigated total, free and protein-bound plasma homocysteine, cys teine and cysteinyl-glycine in 13 subjects aged 24-29 y after a breakf ast at 0900 h containing 15-18 g of protein and a dinner at 1500 h con taining similar to 50 g of protein. Twelve subjects had normal fasting homocysteine (mean +/- SD, 7.6 +/- 1.1 mu mol/L) and methionine conce ntrations (22.7 +/- 3.5 mu mol/L) and were included in the statistical analyses. Breakfast caused a small but significant increase in plasma methionine (22.2 +/- 20.6%) and a brief, nonsignificant increase foll owed by a significant decline in free homocysteine. However, changes i n total and bound homocysteine were small. After dinner, there was a m arked increase in plasma methionine by 16.7 +/- 8.9 mu mol/L (87.9 +/- 49%), which was associated with a rapid and marked increase in free h omocysteine (33.7 +/- 19.6%, 4 h after dinner) and a moderate and slow increase in total (13.5 +/- 7.5%, 8 h) and protein-bound (12.6 +/- 9. 4%, 8 h) homocysteine. After both meals, cysteine and cysteinylglycine concentrations seemed related to changes in homocysteine, because the re were parallel fluctuations in the free:bound ratios of all three th iols. Dietary changes in plasma homocysteine will probably not affect the evaluation of vitamin deficiency states associated with moderate t o severe hyperhomocysteinemia but may be of concern in the risk assess ment of cardiovascular disease in patients with mild hyperhomocysteine mia. Synchronous fluctuations in the free:bound ratio of the plasma am inothiol compounds indicate that biological effects of homocysteine ma y be difficult to separate from effects due to associated changes in o ther aminothiol compounds.