Background. Metabolic syndrome (MetS) represents a collection of markers associated with cardiovascular morbidity and mortality. Due to its high prevalence and steady increase of the occurrence, prevention or management of MetS is of paramount importance. The aim of our study was to evaluate MetS occurrence and extent of oxidative stress by comparing obese adults after diet optimization with untreated controls. Material and methods: Oxidative stress markers (total amount of free radicals, malondialdehyde, allantoin, alpha 1-antiproteinase, GSSG/GSH ratio), total antioxidant capacity and lipid standardized (x-tocopherol were determined in 40 obese people and 48 healthy controls. The obese people were divided into two group A: obese with restricted energy intake with lowered dietary carbohydrates (n=20) and group 13: with the same grade of obesity but without following dietary recommendations (n=20). Results: Group A exhibited lower oxidative stress markers than group B; free radicals (5.18 +/- 1.68 vs 8.43 +/- 3.66 mmol/l, p<0.01), GSSG/GSH ratio (11.74 +/- 5.01 vs 15.38 +/- 5.93 %, p<0.05) and higher antioxidants: lipid standardized a-tocopherol (3.70 +/- 0.51 vs 3.35 +/- 0.60, p<0.05) and ceruloplasmin (0.24 +/- 0.08 vs 0.21 +/- 0.03 g/l, p<0.05), in the course of same grade of obesity. Furthermore MetS occurrence was found significantly lower was in group A. Conclusion: The energy intake restriction by 2000 kJ, mainly due to carbohydrate limitations, was associated with decreased oxidative stress and simultaneously increased lipid-standardized a-tocopherol and ceruloplasmin in obese people. These changes correlated with diminished MetS occurrence by about 50 % (Tab. 3, Ref. 32). Full Text (Free, PDF) www.bmj.sk.