A metabolic study to evaluate nutritional balance, in which subjects have to eat all the foods supplied and maintain a set schedule, is thought to be stressful for the subjects. The effects of stress on the immune system have been studied extensively. However, there are no studies of non-specific immunological changes during a metabolic study. Serum opsonic activity (SOA) is a direct and suitable indicator of non-specific humoral immunity. In this study, we used luminol-dependent chemiluminescence (LmCL) to measure reactive oxygen species (ROS) generation from pooled human neutrophils as an indicator of SOA. We also measured serum immunoglobulin levels and plasma myeloperoxidase (MPO) activity. Eleven female college students took part in this 21 day metabolic study after giving their written informed consent. The results obtained suggest that the metabolic study has almost no effect on immunoglobulin levels. According to MPO levels, neutrophils in vivo may be deactivated to some minor extent. In contrast to these results, peak time (PT) and peak height (PH) of LmCL were changed significantly during the metabolic study. In conclusion, SOA increased during the 21 day metabolic study. There was no significant correlation between SOA and serum immunoglobulin levels on any of the study days.

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