The plasma profile of polyunsaturated fatty acids and serum iron levels were analyzed in alternative nutrition groups of children (15 lactoovovegetarians and 9 vegans). Estimated values were compared with an average group of children on a mixed diet (omnivores, n = 19). Hyposiderinaemia was found in 33% vegetarians and 78% vegans. The corresponding incidence of hyposiderinaemia for children in the control group was 11%. Iron insufficiency has a negative effect on the metabolism of long-chain fatty acids – decrease of d6-desaturase activity. Formation of higher polyunsaturated fatty acids by desaturation and elongation from linoleic and a-linolenic acids is the only possibility in alternative nutrition groups (the dietary source is lacking). The exogenous effects on the arachidonic acid and docosahexaenoic acid levels from intake of egg and milk fat are negligible in lactoovovegetarians – the content and intake of these acids are minimal. The fatty acid index (calculated as product-to-substrate ratio) for the formation of dihomo-g-linolenic acid (20:3/18:2, n-6) was signifi- cantly lower in both alternative nutrition groups vs omnivores and only insignificantly lower in vegans compared to lactoovovegetarians (involved d6-desaturase activity). The index for formation of eicosapentaenoic acid (20:5/18:3 – n-3, involved the d6+d5-desaturase activities) was significantly decreased in vegans compared to lactoovovegetarians. The ratios of arachidonic-to-linoleic acids and docosahexaenoic-to-a-linolenic acids (inclu- ded all desaturase activities in n-6 and n-3 lineage) were also significantly lower in vegans compared to vegetarians (higher incidence of hyposiderinaemia). The discrepancy in alternative nutrition of vegan children is a higher supply of linoleic and a-linolenic acids for the formation of polyunsaturated fatty acids (compared to both omnivores and lactoovovegetarians) and a negative impact of iron insufficiency on their formation (espe- cially wih respect to fatty acids of the n-3 lineage).

        Klíčová slova: children, vegans, lactoovovegetarians, omnivores, iron, polyunsaturated fatty acids.