Fasting is a practice as old as the human species itself. Therefore, the human organism has developed adaptive mechanisms to periods of nutrient deprivation. These are a rarity nowadays and the incidence of metabolic syndrome, neurodegenerative diseases and cancer is constantly increasing. Rooted in religious practices , different regimes of prolonged and intermittent fasting have been recognized and explored as ways of preventing and treating various diseases. This thesis summarizes current knowledge of the effects of fasting on certain aspects of health (weight loss and decrease of cardiovascular risk factors, nervous system function and cancer). Besides the benefit it achieves by reducing energy intake, other mechanisms by which fasting affects human health are not fully clarified. Different hypotheses are being tested in animal models and include signaling pathways alterations, cellular protection mechanisms, induction of autophagy, anti-inflammatory effects and others. In human studies, different fasting regimes have been shown to be as effective as caloric restriction at weight loss and decreasing cardiovascular risk factors. Animal studies have shown fasting to be an effective way to decrease cognitive decline caused by aging and neurodegenerative disease and have demonstrated its effect on improving nervous system trauma recovery and anticonvulsive effects. Fasting has also shown potential to enhance mood and has a positive effect on the subjective impression of well-being. Fasting, as well as caloric restriction, is believed to contribute to prevention of some cancer types and has shown potential to increase the effectiveness of chemotherapy and protect healthy human cells from toxic effects of cytostatic agents. There is still a shortage of major reliable clinical studies on the effectiveness of different fasting regimes and further investigation of their mechanism of action is necessary as well as optimization of fasting regimes in certain indications.