HOMOCYSTEINE INCREASES AS FOLATE DECREASES IN PLASMA OF HEALTHY-MEN DURING SHORT-TERM DIETARY-FOLATE AND METHYL-GROUP RESTRICTION

Ten healthy adult men were fed a diet low in folate and exogenous meth yl groups to study the effects on folate requirement and status. The m en were housed in a metabolic unit for the entire 108-d study. After a 9-d base-line period (P1), the men were fed an amino acid-defined soy bean product diet for 45 d, which provided 25 mu g/d of folate for 30 d (P2) and (with a folate supplement) 99 mu g/d for 15 d (P3). During P2 and P3, the low methionine and choline diet was supplemented with m ethionine for half the subjects to vary the dietary methyl group intak e. The periods were then repeated over the next 54 d (P4-P6), with a c ross-over of methionine intakes in P5 and P6. Restricting dietary meth yl group intake did not increase the dietary folate requirement. Plasm a total homocysteine rose during folate depletion and correlated inver sely with plasma folate; however, the response of homocysteine to chan ges in folate intake varied among individuals from very strong to abse nt. The results support previous suggestions that increased plasma hom ocysteine concentrations provide a marker of functional folate deficie ncy, and further indicate that individuals may differ greatly in their susceptibility to hyperhomocysteinemia due to low folate intakes. Jud ged by the lack of normalization of high homocysteine concentrations d uring folate repletion, the current folate RDA for adult men may not p rovide the expected margin of protection.