Background. Low protein quality and quantity is reported to be a possible risk of alternative nutrition. Pulses contain 18 - 41 % of methionine in relation to reference protein, moreover, its content in cereals is by one half lower. Therefore vegetarians and vegans may have an insufficient intake of sulphur-containing amino acids that may subsequently affect glutathione values (precursors of its synthesis). Methods and Results. In groups of adults on an alternative diet - lactoovovegetarians (n = 47) and vegans (n = 44) aged 19 - 62 years with average duration on a vegetarian or vegan diet of 7.6 and 4.9 years, respectively, glutathione levels (GSH) were measured in erythrocytes (spectrophotometrically), as well as the activity of GSH-dependent enzymes. As nutritional control (n = 42) served an average sample of omnivores selected from a group of 489 examined, apparently healthy subjects of the same age range living in the same region. One to low protein intake (56 % of RDA) exclusively of plant origin significantly lower levels of total proteins were observed in vegans with a 16 % frequency of hypoproteinaemia (vs 0 % in omnivores). In comparison to omnivores a significantly lower glutathione level was found (4.28 ± 0.12 vs 4.84 ± 0.14 mmol/g Hb, P < 0.01). Lactoovovege- tarians because of their protein intake in adequate amounts with a 27 % proportion of animal proteins (dairy products, eggs) consume a balanced mixture of amino acids, which is reflected in total protein levels similar to omnivores and significantly higher values of glutathione - 5.26 ± 0.12 mmol/g Hb, P < 0.05 (intake of glutathione in diet, higher consumption of fruit and vegetable in comparison to omnivores). A sufficient supply of glutathione as the substrate for enzymatic reactions of hydrogen peroxide or lipid hydroperoxide catabolism, as well as for detoxication of xenobiotics, was reflected in lactoovovegetarians in a significantly higher activity of glutathione-peroxidase and glutathione-S-transferase in erythrocytes. Conclusions. Low protein intake exclusively of plant origin, significantly lower protein levels with 16 % frequency of hypoproteinaemia, significantly lower glutathione values in blood in comparison to omnivores and lactoovove- getarians confirm the risk of a vegan diet also in adult age.

        Key words: omnivores, lactoovovegetarians, vegans, protein, glutathione.