and Objectives: Given that fasting can reduce calorie intake, and on the other hand, starvation and reduction of calorie intake are related to immune system, this study was conducted with the purpose of assessing some blood biochemical factors, which sre related to immune system in fasting individuals. Methods: This experimental study is a before-after study. This investigation was performed on 75 male and female fasting individuals aged 25-50 years. Blood samples were obtained once at the

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... ning of Ramadan and once at the end of Ramadan. The levels of C3, C4, blood sugar, serum leptin, cortisol, and WBC and RBC counts, were measured in the blood sample. Results: In this study, the levels of C3, C4, level, cortisol, and blood sugar were significantly increased during fasting period, but leptin level and blood cells counts had no significant changes. Conclusion: Due to a significant increase in some components of complement system, it seems that the immune system is strengthened by fasting.