Vitamin B₁₂, folate, and vitamin B₆ are the main determinants of homocysteinemia. The vegan diet provides no vitamin B₁₂, but also less strict forms of alternative nutrition may suffer from a deficit of this vitamin. The plasma homocysteine level was measured in alternative nutrition groups of adults (lacto- and lactoovovegetarians, n = 62; vegans, n = 32) and compared with the levels in a group consuming traditional diet (n = 59), omnivores). In the group of vegetarians the average homocysteine level is 13.18 vs. 10.19 μmol/l in omnivores; the frequency of hyperhomocysteinemia is 29 vs. 5% in omnivores. In the group of vegans the average homocysteine value is 15.79 μmol/l (53% of the individual values exceeded 15 μmol/l). Omnivores consume the recommended amount of methionine; however, in individuals consuming an alternative diet, the intake of methionine is deficient (assessed by food frequency questionnaire; lower content of methionine in plant proteins). Under conditions of lower methionine availability the remethylation pathway prevails; therefore, vitamin B₁₂ and folate were evaluated in relation to the homocysteine level. The serum vitamin B₁₂ levels are significantly lower in the alternative nutrition groups (214.8 pmol/l in vegetarians, 140.1 pmol/l in vegans vs. 344.7 pmol/l in omnivores); a deficit (<179.0 pmol/l) was found in 26% of the vegetarians and in 78% of the vegans vs. 0% in omnivores. The serum folate levels were within the range of reference values in all groups; however, they were significantly lower in omnivores. The results show that the mild hyperhomocysteinemia in alternative nutrition is a consequence of vitamin B₁₂ deficiency.

Values of homocysteine and lipid parameters were measured in groups of adults consuming alternative nutrition (vegetarians/lactoovo/, vegans) and compared with a group consuming traditional diet (omnivores, general population). Frequency of hyperhomocysteinemia was 53% in the vegans group, 28% in vegetarians vs. 5% in omnivores. In conditions of lower methionine intake (reduced content in plant proteins), the remethylation pathway of homocysteine metabolism prevails and it is vitamin B12 and folate-dependent. The intake of vitamin B12 is equal to zero in vegans; vegetarians consume 124% of the RDA vs. 383% in omnivores. Serum vitamin levels are significantly lower in subjects consuming alternative nutrition with deficiency observed in 24% of vegetarians, 78% of vegans vs. 0% in omnivores. Serum folate levels are within the reference range in all groups. Mild hyperhomocysteinemia in the groups consuming alternative diet is a consequence of vitamin B12 deficiency. Vegetarians and vegans meet the RDA for energy and fat, and have a favourable proportion of saturated, mono- and polyunsaturated fatty acids on total energy intake; the ratio of linoleic/alpha-linolenic acid in their diet corresponds with the recommendations. They have low cholesterol consumption and higher vitamin E and C intake. Optimal fat intake of correct composition is reflected in lower values of atherosclerosis risk factors (cholesterol, LDL-cholesterol, atherogenic index, saturated fatty acids, triacylglycerols), and significantly higher levels of protective substances (linoleic acid, alpha-linolenic acid, HDL-cholesterol, vitamin E, vitamin E/cholesterol, vitamin C). Low lipid risk factors but higher findings of mild hyperhomocysteinemia in vegetarians mean a diminished protective effect of alternative nutrition in cardiovascular disease prevention.