Fasting has been practiced for millennia and is now understood to play a significant role in adaptive cellular responses that reduce oxidative damage, inflammation, and promote energy metabolism. In lower eukaryotes, chronic fasting extends longevity by reprogramming metabolic and stress resistance pathways. In rodents, intermittent or periodic fasting protects against diabetes, cancers, heart disease, and neurodegeneration, while in humans, it helps reduce obesity, hypertension, asthma, and rheumatoid arthritis. Fasting can delay aging and help prevent and treat diseases while minimizing the side effects of chronic dietary interventions. Fasting is distinct from caloric restriction (CR), which involves a chronic reduction in daily caloric intake. Fasting results in ketogenesis, promotes metabolic changes, and can have medical applications, such as reducing seizures and ameliorating rheumatoid arthritis. Studies in various organisms, including bacteria, yeast, and nematodes, show that fasting extends lifespan and enhances stress resistance. In mammals, fasting triggers metabolic adaptations, including the use of ketone bodies and fatty acids for energy, and can improve brain function, neurogenesis, and synaptic plasticity. Fasting has been shown to have beneficial effects on cancer prevention and treatment by reducing glucose, insulin, and IGF-1 levels, which are associated with cancer growth. It also enhances the sensitivity of cancer cells to chemotherapy. In neurodegenerative diseases, fasting reduces oxidative damage, inflammation, and improves neurotrophic factor signaling, which can slow disease progression. In the context of metabolic syndrome, fasting improves insulin sensitivity, reduces body fat, and lowers blood pressure, which are key factors in reducing the risk of cardiovascular disease and diabetes. Fasting has also been shown to have positive effects on inflammation and hypertension, with studies indicating that it can reduce inflammatory markers and lower blood pressure. However, fasting should be carefully managed, especially in vulnerable populations such as the elderly and underweight individuals. It is recommended that fasting be conducted under medical supervision and that individuals choose fasting regimens that are feasible for their lifestyle. Overall, fasting has significant potential to promote health and reduce the risk of chronic diseases, particularly for those who are overweight and sedentary. However, further research is needed to understand the mechanisms of fasting and to develop effective and safe fasting-based interventions for human use.Fasting has been practiced for millennia and is now understood to play a significant role in adaptive cellular responses that reduce oxidative damage, inflammation, and promote energy metabolism. In lower eukaryotes, chronic fasting extends longevity by reprogramming metabolic and stress resistance pathways. In rodents, intermittent or periodic fasting protects against diabetes, cancers, heart disease, and neurodegeneration, while in humans, it helps reduce obesity, hypertension, asthma, and rheumatoid arthritis. Fasting can delay aging and help prevent and treat diseases while minimizing the side effects of chronic dietary interventions. Fasting is distinct from caloric restriction (CR), which involves a chronic reduction in daily caloric intake. Fasting results in ketogenesis, promotes metabolic changes, and can have medical applications, such as reducing seizures and ameliorating rheumatoid arthritis. Studies in various organisms, including bacteria, yeast, and nematodes, show that fasting extends lifespan and enhances stress resistance. In mammals, fasting triggers metabolic adaptations, including the use of ketone bodies and fatty acids for energy, and can improve brain function, neurogenesis, and synaptic plasticity. Fasting has been shown to have beneficial effects on cancer prevention and treatment by reducing glucose, insulin, and IGF-1 levels, which are associated with cancer growth. It also enhances the sensitivity of cancer cells to chemotherapy. In neurodegenerative diseases, fasting reduces oxidative damage, inflammation, and improves neurotrophic factor signaling, which can slow disease progression. In the context of metabolic syndrome, fasting improves insulin sensitivity, reduces body fat, and lowers blood pressure, which are key factors in reducing the risk of cardiovascular disease and diabetes. Fasting has also been shown to have positive effects on inflammation and hypertension, with studies indicating that it can reduce inflammatory markers and lower blood pressure. However, fasting should be carefully managed, especially in vulnerable populations such as the elderly and underweight individuals. It is recommended that fasting be conducted under medical supervision and that individuals choose fasting regimens that are feasible for their lifestyle. Overall, fasting has significant potential to promote health and reduce the risk of chronic diseases, particularly for those who are overweight and sedentary. However, further research is needed to understand the mechanisms of fasting and to develop effective and safe fasting-based interventions for human use.