The effect of diet on plasma homocysteine concentrations in healthy male subjects

Abstract

Objective: To determine the effect of habitual omnivorous and vegetarian diets on folate and vitamin B₁₂ status and the subsequent effect on homocysteine concentration.

Design: Cross-sectional comparison of free-living habitual meat-eaters and habitual vegetarians.

Setting: The study was conducted at RMIT University, Melbourne.

Subjects: One hundred and thirty-nine healthy male subjects (vegans n=18, ovolacto vegetarians n=43, moderate meat-eaters n=60 and high meat-eaters n=18) aged 20–55 y who were recruited in Melbourne.

Outcome measures: Fasting plasma or serum from each subject was analysed for folate, vitamin B₁₂ and homocysteine concentration. A semi-quantitative Food Frequency Questionnaire was completed by a subset of subjects from each group to determine methionine intake.

Results: The two meat eating groups consumed significantly greater levels of methionine (P<0.001). There was no clear trend in plasma folate status between groups, however the plasma vitamin B₁₂ concentration decreased progressively from the high-meat-eating group to vegans (P<0.05). An inverse trend was observed with plasma homocysteine concentration, with vegans showing the highest levels and high meat eaters the lowest (P<0.05).

Conclusions: Dietary methionine intake has no observable effect on plasma homocysteine concentration. In habitual diets, where folate intake is adequate, lowered vitamin B₁₂ intake from animal foods leads to depleted plasma vitamin B₁₂ concentration with a concomitant increase in homocysteine concentration. The suggested mechanism is the failure to transfer a methyl group from methyl tetrahydrofolate by vitamin B₁₂ in the remethylation of homocysteine to methionine.

Sponsorship: The study was funded by the Meat Research Corporation of Australia.