The source is an excerpt from Dave Asprey's book "Fast This Way" in which he discusses the benefits of intermittent fasting and provides a comprehensive guide on how to effectively incorporate fasting into one's lifestyle. Asprey argues that fasting is a powerful tool for improving mental and physical health, shedding weight, and increasing resilience. He explores different fasting methods, including Bulletproof Intermittent Fasting, the 5:2 fast, and alternate-day fasting, along with the benefits of longer fasts. Asprey also emphasizes the importance of managing stress, optimizing sleep, and incorporating exercise into a fasting regimen. The text dives into the evolutionary history of human eating patterns, highlighting how the modern three-meals-a-day diet has led to metabolic dysfunction and chronic health issues. Finally, Asprey offers advice on how to overcome mental obstacles, embrace uncomfortable feelings, and cultivate self-awareness through fasting.